1
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Wang X, Yang Y, Roh S, Hormozi S, Gianneschi NC, Abbott NL. Self-Timed and Spatially Targeted Delivery of Chemical Cargo by Motile Liquid Crystal. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2311311. [PMID: 38422370 DOI: 10.1002/adma.202311311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 02/12/2024] [Indexed: 03/02/2024]
Abstract
A key challenge underlying the design of miniature machines is encoding materials with time- and space-specific functional behaviors that require little human intervention. Dissipative processes that drive materials beyond equilibrium and evolve continuously with time and location represent one promising strategy to achieve such complex functions. This work reports how internal nonequilibrium states of liquid crystal (LC) emulsion droplets undergoing chemotaxis can be used to time the delivery of a chemical agent to a targeted location. During ballistic motion, hydrodynamic shear forces dominate LC elastic interactions, dispersing microdroplet inclusions (microcargo) within double emulsion droplets. Scale-dependent colloidal forces then hinder the escape of dispersed microcargo from the propelling droplet. Upon arrival at the targeted location, a circulatory flow of diminished strength allows the microcargo to cluster within the LC elastic environment such that hydrodynamic forces grow to exceed colloidal forces and thus trigger the escape of the microcargo. This work illustrates the utility of the approach by using microcargo that initiate polymerization upon release through the outer interface of the carrier droplet. These findings provide a platform that utilizes nonequilibrium strategies to design autonomous spatial and temporal functions into active materials.
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Affiliation(s)
- Xin Wang
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Yu Yang
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Sangchul Roh
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
- School of Chemical Engineering, Chonnam National University, Gwangju, 61186, Republic of Korea
| | - Sarah Hormozi
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Nathan C Gianneschi
- Department of Chemistry, Materials Science & Engineering, Biomedical Engineering and Pharmacology, Northwestern University, Evanston, IL, 60208, USA
| | - Nicholas L Abbott
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
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2
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Haputhanthrige NP, Paladugu S, Lavrentovich MO, Lavrentovich OD. Trapping of isotropic droplets by disclinations in nematic liquid crystals controlled by surface anchoring and elastic constant disparity. Phys Rev E 2024; 109:064703. [PMID: 39020964 DOI: 10.1103/physreve.109.064703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2024] [Accepted: 05/24/2024] [Indexed: 07/20/2024]
Abstract
Linear defects such as dislocations and disclinations in ordered materials attract foreign particles since they replace strong elastic distortions at the defect cores. In this work, we explore the behavior of isotropic droplets nucleating at singular disclinations in a nematic liquid crystal, predesigned by surface photopatterning. Experiments show that in the biphasic nematic-isotropic region, although the droplets are attracted to the disclination cores, their centers of mass shift away from the core centers as the temperature increases. The shift is not random, being deterministically defined by the surrounding director field. The effect is explained by the balance of interfacial anchoring and bulk elasticity. An agreement with the experiment can be achieved only if the model accounts for the disparity of the nematic elastic constants; the so-called one-constant approximation, often used in the theoretical analysis of liquid crystals, produces qualitatively wrong predictions. In particular, the experimentally observed shift towards the bend region around a +1/2 disclination core can be explained only when the bend constant is larger than the splay constant. The described dependence of the precise location of a foreign inclusion at defect cores on the elastic and surface anchoring properties can be used in rational design of microscale architectures.
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Affiliation(s)
| | | | - Maxim O Lavrentovich
- Department of Earth, Environment, and Physics, Worcester State University, Worcester, Massachusetts 01602, USA
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Oleg D Lavrentovich
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
- Materials Science Graduate Program, Kent State University, Kent, Ohio 44242, USA
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3
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Rajabi M, Turiv T, Li BX, Baza H, Golovaty D, Lavrentovich OD. High-Order Nonlinear Electrophoresis in a Nematic Liquid Crystal. PHYSICAL REVIEW LETTERS 2024; 132:158102. [PMID: 38682980 DOI: 10.1103/physrevlett.132.158102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2023] [Accepted: 03/21/2024] [Indexed: 05/01/2024]
Abstract
Electrophoresis is the motion of particles relative to a surrounding fluid driven by a uniform electric field. In conventional electrophoresis, the electrophoretic velocity grows linearly with the applied field. Nonlinear effects with a quadratic speed vs field dependence are gaining research interest since an alternating current field could drive them. Here, we report on the giant nonlinearity of electrophoresis in a nematic liquid crystal in which the speed grows with the fourth and sixth powers of the electric field. The mechanism is attributed to the shear thinning of the nematic environment induced by the moving colloid. The observed giant nonlinear effect dramatically enhances the efficiency of electrophoretic transport.
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Affiliation(s)
- Mojtaba Rajabi
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Taras Turiv
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - Bing-Xiang Li
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- College of Electronic and Optical Engineering & College of Flexible Electronics (Future Technology), Nanjing University of Posts and Telecommunications, Nanjing 210023, China
| | - Hend Baza
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Dmitry Golovaty
- Department of Mathematics, The University of Akron, Akron, Ohio 44325-4002, USA
| | - Oleg D Lavrentovich
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
- Materials Science Graduate Program, Kent State University, Kent, Ohio 44242, USA
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4
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Yu H, Gold JI, Wolter TJ, Bao N, Smith E, Zhang HA, Twieg RJ, Mavrikakis M, Abbott NL. Actuating Liquid Crystals Rapidly and Reversibly by Using Chemical Catalysis. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024:e2309605. [PMID: 38331028 DOI: 10.1002/adma.202309605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2023] [Revised: 01/25/2024] [Indexed: 02/10/2024]
Abstract
Microtubules and catalytic motor proteins underlie the microscale actuation of living materials, and they have been used in reconstituted systems to harness chemical energy to drive new states of organization of soft matter (e.g., liquid crystals (LCs)). Such materials, however, are fragile and challenging to translate to technological contexts. Rapid (sub-second) and reversible changes in the orientations of LCs at room temperature using reactions between gaseous hydrogen and oxygen that are catalyzed by Pd/Au surfaces are reported. Surface chemical analysis and computational chemistry studies confirm that dissociative adsorption of H2 on the Pd/Au films reduces preadsorbed O and generates 1 ML of adsorbed H, driving nitrile-containing LCs from a perpendicular to a planar orientation. Subsequent exposure to O2 leads to oxidation of the adsorbed H, reformation of adsorbed O on the Pd/Au surface, and a return of the LC to its initial orientation. The roles of surface composition and reaction kinetics in determining the LC dynamics are described along with a proof-of-concept demonstration of microactuation of beads. These results provide fresh ideas for utilizing chemical energy and catalysis to reversibly actuate functional LCs on the microscale.
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Affiliation(s)
- Huaizhe Yu
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 1 Ho Plaza, Ithaca, NY, 14853, USA
| | - Jake I Gold
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706, USA
| | - Trenton J Wolter
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706, USA
| | - Nanqi Bao
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 1 Ho Plaza, Ithaca, NY, 14853, USA
| | - Evangelos Smith
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706, USA
| | - Hanyu Alice Zhang
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 1 Ho Plaza, Ithaca, NY, 14853, USA
| | - Robert J Twieg
- Department of Chemistry and Biochemistry, Kent State University, 1175 Risman Drive, Kent, OH, 44242, USA
| | - Manos Mavrikakis
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706, USA
| | - Nicholas L Abbott
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 1 Ho Plaza, Ithaca, NY, 14853, USA
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5
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S A, V S D, More P, Pujala RK, Dhara S. Electrophoretic propulsion of matchstick-shaped magnetodielectric particles in the presence of external magnetic fields in a nematic liquid crystal. SOFT MATTER 2024; 20:535-545. [PMID: 38126395 DOI: 10.1039/d3sm01382k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
Synthesis of micro- and nanoparticles of pre-designed shape and surface properties is an integral part of soft and synthetic active matter. We report synthesis of matchstick-shaped (MS) magnetodielectric particles and demonstrate their potential as active agents with field-controllable trajectories in a nematic liquid crystal (NLC). The MS particles with homeotropic anchoring in NLCs align either parallel or perpendicular to the director depending on the dipolar or quadrupolar director distortions. When subjected to transverse electric and magnetic fields, the particles experience electric and magnetic torques trying to align them in the respective field directions. At equilibrium, the long axis is tilted at an angle with respect to the director. The change in orientation alters the surrounding elastic distortion, which results in unbalanced electroosmotic flows. These flows provide the necessary impetus for propelling the particles in various directions with different velocities depending on their orientations.
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Affiliation(s)
- Archana S
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
| | - Devika V S
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
| | - Prasanna More
- Department of Physics, Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati, Andhra Pradesh, 517507, India
| | - Ravi Kumar Pujala
- Department of Physics, Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati, Andhra Pradesh, 517507, India
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
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6
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Yao T, Kos Ž, Zhang QX, Luo Y, Steager EB, Ravnik M, Stebe KJ. Topological defect-propelled swimming of nematic colloids. SCIENCE ADVANCES 2022; 8:eabn8176. [PMID: 36001658 PMCID: PMC10939095 DOI: 10.1126/sciadv.abn8176] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 07/12/2022] [Indexed: 06/15/2023]
Abstract
Topological defects on colloids rotating in nematic liquid crystals form far-from-equilibrium structures that perform complex swim strokes in which the defects periodically extend, depin, and contract. These defect dynamics propel the colloid, generating translation from rotation. The swimmer's speed and direction are determined by the topological defect's polarity and extent of elongation. Defect elongation is controlled by a rotating external magnetic field, allowing control over particle trajectories. The swimmers' translational motion relies on broken symmetries associated with lubrication forces between the colloid and the bounding surfaces, line tensions associated with the elongated defect, and anisotropic viscosities associated with the defect elongation adjacent to the colloid. The scattering or effective pair interaction of these swimmers is highly anisotropic, with polarization-dependent dimer stability and motion that depend strongly on entanglement and sharing of their extended defect structures. This research introduces transient, far-from-equilibrium topological defects as a class of virtual functional structures that generate modalities of motion and interaction.
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Affiliation(s)
- Tianyi Yao
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Žiga Kos
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
- Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Qi Xing Zhang
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Yimin Luo
- Department of Chemical Engineering, University of California, Santa Barbara, CA 93106, USA
| | - Edward B. Steager
- Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Miha Ravnik
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
- Condensed Matter Physics Department, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Kathleen J. Stebe
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
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7
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Guo YQ, Chu F, Li BX, Zhang YX, Shen TZ, Duan W, Liu C, Sun YB, Wang QH. Unidirectional collective transport of microspheres in nematic liquid crystal by electrically tunable reorientation. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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8
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Xu Y, Chang Y, Yao Y, Zhang M, Dupont RL, Rather AM, Bao X, Wang X. Modularizable Liquid-Crystal-Based Open Surfaces Enable Programmable Chemical Transport and Feeding using Liquid Droplets. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2108788. [PMID: 35333418 DOI: 10.1002/adma.202108788] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/10/2021] [Indexed: 06/14/2023]
Abstract
Droplet-based miniature reactors have attracted interest in both fundamental studies, for the unique reaction kinetics they enable, and applications in bio-diagnosis and material synthesis. However, the precise and automatic feeding of chemicals, important for the delicate reactions in these miniaturized chemical reactors, either requires complex, high-cost microfluidic devices or lacks the capability to maintain a pinning-free droplet movement. Here, the design and synthesis of a new class of liquid crystal (LC)-based open surfaces, which enable a controlled chemical release via a programmable LC phase transition without sacrificing the free transport of the droplets, are reported. It is demonstrated that their intrinsic slipperiness and self-healing properties enable a modularizable assembly of LC surfaces that can be loaded with different chemicals to achieve a wide range of chemical reactions carried out within the droplets, including sequential and parallel chemical reactions, crystal growth, and polymer synthesis. Finally, an LC-based chemical feeding device is developed that can automatically control the release of chemicals to direct the simultaneous differentiation of human induced pluripotent stem cells into endothelial progenitor cells and cardiomyocytes. Overall, these LC surfaces exhibit desirable levels of automation, responsiveness, and controllability for use in miniature droplet carriers and reactors.
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Affiliation(s)
- Yang Xu
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
| | - Yun Chang
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Yuxing Yao
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Meng Zhang
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
| | - Robert L Dupont
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
| | - Adil M Rather
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
| | - Xiaoping Bao
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Xiaoguang Wang
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
- Sustainability Institute, The Ohio State University, Columbus, OH, 43210, USA
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9
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Sahu DK, Dhara S. Electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in nematic liquid crystals. SOFT MATTER 2022; 18:1819-1824. [PMID: 35166748 DOI: 10.1039/d1sm01653a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
We study the electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in two nematic liquid crystals (LCs) having the same sign of conductivity anisotropy (Δσ) but opposite signs of dielectric anisotropy (Δε). The applied ac electric field is parallel and perpendicular to the director for positive and negative dielectric anisotropy LCs, respectively. We show that the Janus dipolar particles propel faster than the non-Janus dipolar particles in both LCs. The propelling speed of the Janus dipolar particles is also significantly higher compared to the quadrupolar Janus particles studied previously. We map the electroosmotic flow fields surrounding a Janus dipolar particle using microparticle image velocimetry (μ-PIV) and show that the flow on a metal hemisphere is stronger than that on a dielectric hemisphere. Altogether, Janus dipolar particles demonstrate efficient electrophoresis compared to both Janus and non-Janus quadrupolar particles. These findings may be useful for applications in active matter, microrobotic and microfluidic devices.
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Affiliation(s)
- Dinesh Kumar Sahu
- School of Physics, University of Hyderabad, Hyderabad 500 046, India.
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad 500 046, India.
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10
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Wang X, Sun H, Kim YK, Wright DB, Tsuei M, Gianneschi NC, Abbott NL. Stimuli-Responsive Liquid Crystal Printheads for Spatial and Temporal Control of Polymerization. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2106535. [PMID: 35065542 DOI: 10.1002/adma.202106535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 12/23/2021] [Indexed: 06/14/2023]
Abstract
Polymerization reactions triggered by stimuli play a pivotal role in materials science, with applications ranging from lithography to biomedicine to adaptive materials. However, the development of chemically triggered, stimuli-responsive systems that can confer spatial and temporal control on polymerization remains a challenge. Herein, chemical-stimuli-induced polymerization based on a liquid crystal (LC) printhead is presented. The LC responds to a local chemical stimulus at its aqueous interface, resulting in the ejection of initiator into the solution to trigger polymerization. Various LC printhead geometries are designed, allowing programming of: i) bulk solution polymerization, ii) synthesis of a thin surface-confined polymeric coating, iii) polymerization-induced self-assembly of block copolymers to form various nanostructures (sphere, worm-like, and vesicles), and iv) 3D polymeric structures printed according to local solution conditions. The approach is demonstrated using amphiphiles, multivalent ions, and biomolecules as stimuli.
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Affiliation(s)
- Xin Wang
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Hao Sun
- Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA
| | - Young-Ki Kim
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Daniel B Wright
- Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA
| | - Michael Tsuei
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
| | | | - Nicholas L Abbott
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14850, USA
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11
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Senyuk B, Adufu RE, Smalyukh II. Electrically Powered Locomotion of Dual-Nature Colloid-Hedgehog and Colloid-Umbilic Topological and Elastic Dipoles in Liquid Crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:689-697. [PMID: 34990137 DOI: 10.1021/acs.langmuir.1c02546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Colloidal particles in liquid crystals tend to induce topological defects and distortions of the molecular alignment within the surrounding anisotropic host medium, which results in elasticity-mediated interactions not accessible to their counterparts within isotropic fluid hosts. Such particle-induced coronae of perturbed nematic order are highly responsive to external electric fields, even when the uniformly aligned host medium away from particles exhibits no response to fields below the realignment threshold. Here we harness the nonreciprocal nature of these facile electric responses to demonstrate colloidal locomotion. Oscillations of the electric field prompt repetitive deformations of the corona of dipolar elastic distortions around the colloidal inclusions, which upon appropriately designed electric driving synchronize the displacement directions. We observe the colloid-hedgehog dipole accompanied by an umbilical defect in the tilt directionality field (c-field), along with the texture of elastic distortions that evolves with a change in the applied voltage. The temporal out-of-equilibrium evolution of the director and c-field distortions around particles when the voltage is turned on and off is not invariant upon reversal of time, prompting lateral translations and interactions that markedly differ from those accessible to these colloids under equilibrium conditions. Our findings may lead to both technological and fundamental science applications of nematic colloids as both model reconfigurable colloidal systems and as mesostructured materials with predesigned temporal evolution of structure and composition.
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Affiliation(s)
- Bohdan Senyuk
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
| | - Richmond E Adufu
- Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Ivan I Smalyukh
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
- Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, Colorado 80309, United States
- Soft Materials Research Center and Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
- Chemical Physics Program, Departments of Chemistry and Physics, University of Colorado, Boulder, Colorado 80309, United States
- Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory and University of Colorado, Boulder, Colorado 80309, United States
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12
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Xu Y, Rather AM, Yao Y, Fang JC, Mamtani RS, Bennett RKA, Atta RG, Adera S, Tkalec U, Wang X. Liquid crystal-based open surface microfluidics manipulate liquid mobility and chemical composition on demand. SCIENCE ADVANCES 2021; 7:eabi7607. [PMID: 34597134 PMCID: PMC10938512 DOI: 10.1126/sciadv.abi7607] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 08/10/2021] [Indexed: 05/22/2023]
Abstract
The ability to control both the mobility and chemical compositions of microliter-scale aqueous droplets is an essential prerequisite for next-generation open surface microfluidics. Independently manipulating the chemical compositions of aqueous droplets without altering their mobility, however, remains challenging. In this work, we address this challenge by designing a class of open surface microfluidic platforms based on thermotropic liquid crystals (LCs). We demonstrate, both experimentally and theoretically, that the unique positional and orientational order of LC molecules intrinsically decouple cargo release functionality from droplet mobility via selective phase transitions. Furthermore, we build sodium sulfide–loaded LC surfaces that can efficiently precipitate heavy metal ions in sliding water droplets to final concentration less than 1 part per million for more than 500 cycles without causing droplets to become pinned. Overall, our results reveal that LC surfaces offer unique possibilities for the design of novel open surface fluidic systems with orthogonal functionalities.
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Affiliation(s)
- Yang Xu
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Adil M. Rather
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Yuxing Yao
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Jen-Chun Fang
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Rajdeep S. Mamtani
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Robert K. A. Bennett
- Department of Electrical and Computer Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Richard G. Atta
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
| | - Solomon Adera
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Uroš Tkalec
- Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia
- Department of Condensed Matter Physics, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Xiaoguang Wang
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
- Sustainability Institute, The Ohio State University, Columbus, OH 43210, USA
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13
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M MR, Pujala RK, Paladugu S, Dhara S. Interactions of charged microrods in chiral nematic liquid crystals. Phys Rev E 2021; 104:014706. [PMID: 34412267 DOI: 10.1103/physreve.104.014706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Accepted: 07/02/2021] [Indexed: 11/07/2022]
Abstract
We study the pair interaction of charged silica microrods in chiral nematic liquid crystals and show that the microrods with homeotropic surface anchoring form a bound state due to the competing effect of electrostatic (Coulomb) and elastic interactions. The robustness of the bound state is demonstrated by applying external electrical and mechanical forces that perturbs their equilibrium position as well as orientation. In the bound state we have measured the correlated thermal fluctuations of the position, using two-particle cross-correlation spectroscopy that uncovers their hydrodynamic interaction. These findings reveal unexplored aspects of liquid-crystal dispersions which are important for understanding the assembly and dynamics of nano- and microparticles in chiral nematic liquid crystals.
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Affiliation(s)
- Muhammed Rasi M
- School of Physics, University of Hyderabad, Hyderabad 500046, India
| | - Ravi Kumar Pujala
- Department of Physics, Indian Institute of Science Education and Research, Tirupati, Andhra Pradesh 517507, India
| | - Sathyanarayana Paladugu
- Department of Physics, Indian Institute of Science Education and Research, Tirupati, Andhra Pradesh 517507, India
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad 500046, India
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14
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Krishnamurthy KS, Shankar Rao DS, Kanakala MB, Yelamaggad CV. Electric response of topological dipoles in nematic colloids with twist-bend nematic droplets as the dispersed phase. Phys Rev E 2021; 103:042701. [PMID: 34005968 DOI: 10.1103/physreve.103.042701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Accepted: 03/15/2021] [Indexed: 06/12/2023]
Abstract
Colloidal systems comprising solid or fluid particles dispersed in nematic monodomains are known to be a convenient means to study topological defects. Recent experiments have shown that twist-bend nematic (N_{TB}) droplets in a nematic matrix act as colloidal particles that lead to the formation of elastic dipoles, quadrupoles, and their ordered clusters. In this study, we examine the effect of low-frequency (f∼mHz) electric fields on such defect configurations. We find that (i) the hyperbolic hedgehogs of elastic dipoles shift toward the negative electrode in static fields and perform oscillatory motion in AC fields, indicating the presence of nonvanishing flexoelectric polarization in the field-free state; (ii) the elastic dipoles, propelled by forces of backflow due to coupled flexoelectric and dielectric distortions, drift uniformly along their axes with the N_{TB} drops in lead; (iii) the translational velocity v_{d} increases linearly with both f and the diameter of N_{TB} drops; and (iv) with increasing applied voltage U, v_{d}(U) exhibits a monotonic, slightly nonlinear variation at f≤200mHz, tending toward linearity at higher frequencies.
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Affiliation(s)
- K S Krishnamurthy
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
| | - D S Shankar Rao
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
| | - Madhu B Kanakala
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
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15
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Zhang J, Guo Y, Hu W, Soon RH, Davidson ZS, Sitti M. Liquid Crystal Elastomer-Based Magnetic Composite Films for Reconfigurable Shape-Morphing Soft Miniature Machines. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2006191. [PMID: 33448077 PMCID: PMC7610459 DOI: 10.1002/adma.202006191] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 11/30/2020] [Indexed: 05/08/2023]
Abstract
Stimuli-responsive and active materials promise radical advances for many applications. In particular, soft magnetic materials offer precise, fast, and wireless actuation together with versatile functionality, while liquid crystal elastomers (LCEs) are capable of large reversible and programmable shape-morphing with high work densities in response to various environmental stimuli, e.g., temperature, light, and chemical solutions. Integrating the orthogonal stimuli-responsiveness of these two kinds of active materials could potentially enable new functionalities and future applications. Here, magnetic microparticles (MMPs) are embedded into an LCE film to take the respective advantages of both materials without compromising their independent stimuli-responsiveness. This composite material enables reconfigurable magnetic soft miniature machines that can self-adapt to a changing environment. In particular, a miniature soft robot that can autonomously alter its locomotion mode when it moves from air to hot liquid, a vine-like filament that can sense and twine around a support, and a light-switchable magnetic spring are demonstrated. The integration of LCEs and MMPs into monolithic structures introduces a new dimension in the design of soft machines and thus greatly enhances their use in applications in complex environments, especially for miniature soft robots, which are self-adaptable to environmental changes while being remotely controllable.
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Affiliation(s)
- Jiachen Zhang
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
| | - Yubing Guo
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
| | - Wenqi Hu
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
| | - Ren Hao Soon
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
| | - Zoey S Davidson
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
| | - Metin Sitti
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, 70569, Germany
- Department of Information Technology and Electrical Engineering, ETH Zürich, Zürich, 8092, Switzerland
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16
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Paladugu S, Kaur S, Mohiuddin G, Pujala RK, Pal SK, Dhara S. Microrheology to probe smectic clusters in bent-core nematic liquid crystals. SOFT MATTER 2020; 16:7556-7561. [PMID: 32706008 DOI: 10.1039/d0sm00796j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Many bent-core nematic liquid crystals exhibit unusual physical properties due to the presence of smectic clusters, known as "cybotactic" clusters, in the nematic phase. Here, we investigate the effect of these clusters on the complex shear modulus (G*(ω)) of two asymmetric bent-core liquid crystals using a microrheological technique. The compound with a shorter hydrocarbon chain (8OCH3) exhibits only a nematic (N) phase whereas the compound with a longer chain (16OCH3) exhibits both nematic (N) and smectic-A (SmA) phases. The rheological results are correlated with the measurements of curvature elastic constants. Our results show that the directional shear modulus of 16OCH3, just above the SmA to N phase transition temperature, is strikingly different than that of 8OCH3, owing to the smectic clusters. An approximate size of the clusters is estimated using a simple model. Therefore, microrheological studies on bent-core nematic liquid crystals are very useful in extracting information about underlying smectic clusters.
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Affiliation(s)
- Sathyanarayana Paladugu
- School of Physics, University of Hyderabad, Hyderabad, India. and Soft and Active Matter Group, Department of Physics, Indian Institute of Science Education and Research (IISER), Tirupati, Andhra Pradesh 517507, India
| | - Supreet Kaur
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector-81, Knowledge City, Manauli 140306, India
| | - Golam Mohiuddin
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector-81, Knowledge City, Manauli 140306, India
| | - Ravi Kumar Pujala
- Soft and Active Matter Group, Department of Physics, Indian Institute of Science Education and Research (IISER), Tirupati, Andhra Pradesh 517507, India
| | - Santanu Kumar Pal
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector-81, Knowledge City, Manauli 140306, India
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad, India.
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17
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Akdeniz B, Batir O, Bukusoglu E. Identification and sorting of particle chirality using liquid crystallinity. J Colloid Interface Sci 2020; 574:11-19. [PMID: 32298977 DOI: 10.1016/j.jcis.2020.04.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 03/30/2020] [Accepted: 04/01/2020] [Indexed: 10/24/2022]
Abstract
Particles dispersed in liquid crystals (LCs) have been shown to assemble due to the elastic interactions arising from the molecular anisotropy. Studies have shown that the alignment of the particles within LCs were strongly dependent on the surface director of LCs on particles. Different from the past studies involving particles with degenerate planar anchoring of LCs, this study shows that the azimuthal surface director can be used to control and finely tune the positioning of the particles in LCs. Specifically, polymeric particles with two flat surfaces that mediate parallel or non-parallel (chiral) anchoring were synthesized and dispersed in nematic 5CB with spatial variations in the director profile. Besides demonstration of their positioning, it was observed that the particles with same chiral handedness with the LC twist were distributed within the LC film, whereas particles with opposite handedness were repelled from the LC medium due to the elastic energy contributions. In addition, a pronounced effect of the surface anchoring of the particles were present on their orientation during non-equilibrium events such as sedimentation. Overall, the studies presented here will find potential use in sensors, separations, optics or soft robotic applications that will take advantages of chirality or chiral interactions.
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Affiliation(s)
- Burak Akdeniz
- Department of Chemical Engineering, Middle East Technical University, Dumlupinar Bulvari No. 1, Çankaya, Ankara 06800, Turkey
| | - Ozge Batir
- Department of Chemical Engineering, Middle East Technical University, Dumlupinar Bulvari No. 1, Çankaya, Ankara 06800, Turkey
| | - Emre Bukusoglu
- Department of Chemical Engineering, Middle East Technical University, Dumlupinar Bulvari No. 1, Çankaya, Ankara 06800, Turkey.
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18
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Xiao K, Chen X, Cao XZ, Wu CX. Field-triggered vertical positional transition of a microparticle suspended in a nematic liquid crystal cell. Phys Rev E 2020; 101:052706. [PMID: 32575330 DOI: 10.1103/physreve.101.052706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2020] [Accepted: 05/11/2020] [Indexed: 11/07/2022]
Abstract
In this paper, based on the numerical calculation of total energy utilizing the Green's function method, we investigate how a field-triggered vertical positional transition of a microparticle suspended in a nematic liquid crystal cell is influenced by the direction of the applied field, surface anchoring feature, and nematic's dielectric properties. The new equilibrium position of the translational movement is decided via a competition between the buoyant force and the effective force built on the microparticle by the elastic energy gradient along the vertical direction. The threshold value of external field depends on thickness L and Frank elastic constant K and slightly on the microparticle size and density, in a Fréedericksz-like manner, but by a factor. For a nematic liquid crystal cell with planar surface alignment, a bistable equilibrium structure for the transition is found when the direction of the applied electric field is (a) perpendicular to the two plates of the cell with positive molecular dielectric anisotropy or (b) parallel to the two plates and the anchoring direction of the cell with negative molecular dielectric anisotropy. When the electric field applied is parallel to both plates and perpendicular to the anchoring direction, the microparticle suspended in the nematic liquid crystal tends to be trapped in the midplane, regardless of the sign of the molecular dielectric anisotropy. Such a phenomenon also occurs for negative molecular dielectric anisotropy if the external field is applied perpendicular to the two plates. Explicit formulas proposed for the critical electric field agree extremely well with the numerical calculation.
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Affiliation(s)
- Ke Xiao
- Department of Physics, School of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China
| | - Xi Chen
- Department of Physics, School of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China
| | - Xue-Zheng Cao
- Department of Physics, School of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China
| | - Chen-Xu Wu
- Department of Physics, School of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China
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19
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Kos Ž, Ravnik M. Field generated nematic microflows via backflow mechanism. Sci Rep 2020; 10:1446. [PMID: 31996700 PMCID: PMC6989461 DOI: 10.1038/s41598-020-57944-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 11/26/2019] [Indexed: 01/08/2023] Open
Abstract
Generation of flow is an important aspect in microfluidic applications and generally relies on external pumps or embedded moving mechanical parts which pose distinct limitations and protocols on the use of microfluidic systems. A possible approach to avoid moving mechanical parts is to generate flow by changing some selected property or structure of the fluid. In fluids with internal orientational order such as nematic liquid crystals, this process of flow generation is known as the backflow effect. In this article, we demonstrate the contact-free generation of microfluidic material flows in nematic fluids -including directed contact-free pumping- by external electric and optical fields based on the dynamic backflow coupling between nematic order and material flow. Using numerical modelling, we design efficient shaping and driving of the backflow-generated material flow using spatial profiles and time modulations of electric fields with oscillating amplitude, rotating electric fields and optical fields. Particularly, we demonstrate how such periodic external fields generate efficient net average nematic flows through a microfluidic channel, that avoid usual invariance under time-reversal limitations. We show that a laser beam with rotating linear polarization can create a vortex-like flow structure and can act as a local flow pump without moving mechanical parts. The work could be used for advanced microfluidic applications, possibly by creating custom microfluidic pathways without predefined channels based on the adaptivity of an optical set-up, with a far reaching unconventional idea to realize channel-less microfluidics.
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Affiliation(s)
- Žiga Kos
- University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000, Ljubljana, Slovenia
| | - Miha Ravnik
- University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000, Ljubljana, Slovenia.
- Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia.
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20
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Kim YK, Noh J, Nayani K, Abbott NL. Soft matter from liquid crystals. SOFT MATTER 2019; 15:6913-6929. [PMID: 31441481 DOI: 10.1039/c9sm01424a] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Liquid crystals (LCs) are fluids within which molecules exhibit long-range orientational order, leading to anisotropic properties such as optical birefringence and curvature elasticity. Because the ordering of molecules within LCs can be altered by weak external stimuli, LCs have been widely used to create soft matter systems that respond optically to electric fields (LC display), temperature (LC thermometer) or molecular adsorbates (LC chemical sensor). More recent studies, however, have moved beyond investigations of optical responses of LCs to explore the design of complex LC-based soft matter systems that offer the potential to realize more sophisticated functions (e.g., autonomous, self-regulating chemical responses to mechanical stimuli) by directing the interactions of small molecules, synthetic colloids and living cells dispersed within the bulk of LCs or at their interfaces. These studies are also increasingly focusing on LC systems driven beyond equilibrium states. This review presents one perspective on these advances, with an emphasis on the discovery of fundamental phenomena that may enable new technologies. Three areas of progress are highlighted; (i) directed assembly of amphiphilic molecules either within topological defects of LCs or at aqueous interfaces of LCs, (ii) templated polymerization in LCs via chemical vapor deposition, an approach that overcomes fundamental challenges related to control of LC phase behavior during polymerization, and (iii) studies of colloids in LCs, including chiral colloids, soft colloids that are strained by LCs, and active colloids that are driven into organized states by dissipation of energy (e.g. bacteria). These examples, and key unresolved issues discussed at the end of this perspective, serve to convey the message that soft matter systems that integrate ideas from LC, surfactant, polymer and colloid sciences define fertile territory for fundamental studies and creation of future transformative technologies.
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Affiliation(s)
- Young-Ki Kim
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 113 Ho Plaza, Ithaca, New York 14853, USA. and Department of Chemical Engineering, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, Gyengbuk 37673, Korea
| | - JungHyun Noh
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 113 Ho Plaza, Ithaca, New York 14853, USA.
| | - Karthik Nayani
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 113 Ho Plaza, Ithaca, New York 14853, USA.
| | - Nicholas L Abbott
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 113 Ho Plaza, Ithaca, New York 14853, USA.
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21
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Luo Y, Yao T, Beller DA, Serra F, Stebe KJ. Deck the Walls with Anisotropic Colloids in Nematic Liquid Crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:9274-9285. [PMID: 31259559 DOI: 10.1021/acs.langmuir.9b01811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Nematic liquid crystals (NLCs) offer remarkable opportunities to direct colloids to form complex structures. The elastic energy field that dictates colloid interactions is determined by the NLC director field, which is sensitive to and can be controlled by boundaries including vessel walls and colloid surfaces. By molding the director field via liquid-crystal alignment on these surfaces, elastic energy landscapes can be defined to drive structure formation. We focus on colloids in otherwise defect-free director fields formed near undulating walls. Colloids can be driven along prescribed paths and directed to well-defined docking sites on such wavy boundaries. Colloids that impose strong alignment generate topologically required companion defects. Configurations for homeotropic colloids include a dipolar structure formed by the colloid and its companion hedgehog defect or a quadrupolar structure formed by the colloid and its companion Saturn ring. Adjacent to wavy walls with wavelengths larger than the colloid diameter, spherical particles are attracted to locations along the wall with distortions in the nematic director field that complement those from the colloid. This is the basis of lock-and-key interactions. Here, we study ellipsoidal colloids with homeotropic anchoring near complex undulating walls. The walls impose distortions that decay with distance from the wall to a uniform director in the far field. Ellipsoids form dipolar defect configurations with the colloid's major axis aligned with the far field director. Two distinct quadrupolar defect structures also form, stabilized by confinement; these include the Saturn I configuration with the ellipsoid's major axis aligned with the far field director and the Saturn II configuration with the major axis perpendicular to the far field director. The ellipsoid orientation varies only weakly in bulk and near undulating walls. All configurations are attracted to walls with long, shallow waves. However, for walls with wavelengths that are small compared to the colloid length, Saturn II is repelled, allowing selective docking of aligned objects. Deep, narrow wells prompt the insertion of a vertical ellipsoid. By introducing an opening at the bottom of such a deep well, we study colloids within pores that connect two domains. Ellipsoids with different aspect ratios find different equilibrium positions. An ellipsoid of the right dimension and aspect ratio can plug the pore, creating a class of 2D selective membranes.
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Affiliation(s)
- Yimin Luo
- Department of Chemical and Biomolecular Engineering , University of Delaware , Newark , Delaware 19716 , United States
| | - Tianyi Yao
- Department of Chemical and Biomolecular Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
| | - Daniel A Beller
- Department of Physics , University of California , Merced , California 95343 , United States
| | - Francesca Serra
- Department of Physics and Astronomy , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Kathleen J Stebe
- Department of Chemical and Biomolecular Engineering , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States
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22
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Boniello G, Luo Y, Beller DA, Serra F, Stebe KJ. Colloids in confined liquid crystals: a plot twist in the lock-and-key mechanism. SOFT MATTER 2019; 15:5220-5226. [PMID: 31172164 DOI: 10.1039/c9sm00788a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
By confining soft materials within tailored boundaries it is possible to design energy landscapes to address and control colloidal dynamics. This provides unique opportunities to create reconfigurable, hierarchically organized structures, a leading challenge in materials science. Example soft matter systems include liquid crystals. For instance, when nematic liquid crystals (NLCs) are confined in a vessel with undulated boundaries, bend and splay distortions can be used to position particles. Here we confine this system in a twist cell. We also study cholesteric liquid crystals, which have an "intrinsic" twist distortion which adds to the ones imposed by the solid boundaries. The cholesteric pitch competes with the other length scales in the system (colloid radius, vessel thickness, wavelength of boundary undulations), enriching the possible configurations. Depending on the pitch-to-radius and pitch-to-thickness ratios the interaction can be attractive or repulsive. By tuning the pitch (i.e. changing the concentration of the chiral dopant), it is possible to selectively promote or inhibit particle trapping at the docking sites.
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Affiliation(s)
- Giuseppe Boniello
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Yimin Luo
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Daniel A Beller
- Department of Physics, University of California, Merced, CA 95343, USA
| | - Francesca Serra
- Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA.
| | - Kathleen J Stebe
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
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23
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Babakhanova G, Yu H, Chaganava I, Wei QH, Shiller P, Lavrentovich OD. Controlled Placement of Microparticles at the Water-Liquid Crystal Elastomer Interface. ACS APPLIED MATERIALS & INTERFACES 2019; 11:15007-15013. [PMID: 30912438 DOI: 10.1021/acsami.8b22023] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Controlled placement of microparticles is of prime importance in production of microscale superstructures. In this work, we demonstrate the remote control of microparticle placement using a photoactivated surface profile of a liquid crystal elastomer (LCE) coating. We employ light-responsive LCEs with preimposed patterns of molecular orientation (director) in the plane of coating. Upon UV illumination, these in-plane director distortions translate into deterministic topographic change of the LCE coating. Microparticles placed at the interface between the LCE coating and water, guided by gravity, gather at the bottom of photoinduced troughs. The effect is reversible: when the substrates are irradiated with visible light, the coatings become flat and the microparticle arrays disorganize again. The proposed noncontact manipulation of particles by photoactivated LCEs may be useful in development of drug delivery or tissue engineering applications.
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Affiliation(s)
| | | | - Irakli Chaganava
- Institute of Cybernetics of Georgian Technical University , Tbilisi 0186 , Georgia
- Georgian State Teaching University of Physical Education and Sport , Tbilisi 0162 , Georgia
| | | | - Paul Shiller
- Civil Engineering-Timken Engineered Surface Laboratory , The University of Akron , Akron 44325 , United States
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24
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Ohzono T. Site-specific attraction dynamics of surface colloids driven by gradients of liquid crystalline distortions. SOFT MATTER 2019; 15:983-988. [PMID: 30656344 DOI: 10.1039/c8sm02404a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The site-specific migration dynamics of small particles at the air-nematic liquid crystal (LC) interface is investigated, using a LC film with a unique gradient of LC distortions. This gradient has been identified as the direct origin of the site-specific migration, while the elastic multipole interaction between the pre-existing distortion and that induced around particles is negligible. The results reveal a basic behavior of small particles with weak anchoring strength in LC distortions, which is often hidden in prominent elastic multipole interactions typically found with larger particles. Moreover, the present mechanism of the site-specific attraction of particles is specifically relevant to directed patterning and manipulations of nano-particles in nematic LCs with distortions.
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Affiliation(s)
- Takuya Ohzono
- Research Institute for Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Higashi, Tsukuba 305-8565, Japan.
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25
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Prodanov MF, Popova EV, Gamzaeva SA, Fedoryako AP, Vashchenko VV. Ferromagnetic nanoparticles in a ferroelectric liquid crystal: Properties of stable colloids in homogeneous cells. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2017.12.123] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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26
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27
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Podgornov FV, Ryzhkova AV, Haase W. Dynamics of nonlinear electrophoretic motion of dielectric microparticles in nematic liquid crystal. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.02.053] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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28
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Kim YK, Wang X, Mondkar P, Bukusoglu E, Abbott NL. Self-reporting and self-regulating liquid crystals. Nature 2018; 557:539-544. [DOI: 10.1038/s41586-018-0098-y] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 03/02/2018] [Indexed: 02/01/2023]
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29
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Chen K, Gebhardt OJ, Devendra R, Drazer G, Kamien RD, Reich DH, Leheny RL. Colloidal transport within nematic liquid crystals with arrays of obstacles. SOFT MATTER 2017; 14:83-91. [PMID: 29099121 DOI: 10.1039/c7sm01681f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We have investigated the gravity-driven transport of spherical colloids suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) within microfluidic arrays of cylindrical obstacles arranged in a square lattice. Homeotropic anchoring at the surfaces of the obstacles created periodic director-field patterns that strongly influenced the motion of the colloids, whose surfaces had planar anchoring. When the gravitational force was oriented parallel to a principal axis of the lattice, the particles moved along channels between columns of obstacles and displayed pronounced modulations in their velocity. Quantitative analysis indicates that this modulation resulted from a combination of a spatially varying effective drag viscosity and elastic interactions engendered by the periodic director field. The interactions differed qualitatively from a sum of pair-wise interactions between the colloids and isolated obstacles, reflecting the distinct nematic environment created by confinement within the array. As the angle α between the gravitational force and principal axis of the lattice was varied, the velocity did not follow the force but instead locked into a discrete set of directions commensurate with the lattice. The transitions between these directions occurred at values of α that were different from those observed when the spheres were in an isotropic liquid, indicating the ability of the liquid crystal forces to tune the lateral displacement behavior in such devices.
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Affiliation(s)
- Kui Chen
- Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, USA.
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30
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Senyuk B, Liu Q, Nystrom PD, Smalyukh II. Repulsion-attraction switching of nematic colloids formed by liquid crystal dispersions of polygonal prisms. SOFT MATTER 2017; 13:7398-7405. [PMID: 28951927 DOI: 10.1039/c7sm01186e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Self-assembly of colloidal particles due to elastic interactions in nematic liquid crystals promises tunable composite materials and can be guided by exploiting surface functionalization, geometric shape and topology, though these means of controlling self-assembly remain limited. Here, we realize low-symmetry achiral and chiral elastic colloids in the nematic liquid crystals using colloidal polygonal concave and convex prisms. We show that the controlled pinning of disclinations at the prism edges alters the symmetry of director distortions around the prisms and their orientation with respect to the far-field director. The controlled localization of the disclinations at the prism's edges significantly influences the anisotropy of the diffusion properties of prisms dispersed in liquid crystals and allows one to modify their self-assembly. We show that elastic interactions between polygonal prisms can be switched between repulsive and attractive just by controlled re-pinning the disclinations at different edges using laser tweezers. Our findings demonstrate that elastic interactions between colloidal particles dispersed in nematic liquid crystals are sensitive to the topologically equivalent but geometrically rich controlled configurations of the particle-induced defects.
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Affiliation(s)
- B Senyuk
- Department of Physics and Soft Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
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31
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Orihara H, Sakurai N, Sasaki Y, Nagaya T. Direct observation of coupling between orientation and flow fluctuations in a nematic liquid crystal at equilibrium. Phys Rev E 2017; 95:042705. [PMID: 28505722 DOI: 10.1103/physreve.95.042705] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Indexed: 11/07/2022]
Abstract
To demonstrate coupling between orientation and flow fluctuations in a nematic liquid crystal at equilibrium, we simultaneously observe the intensity change due to director fluctuations under a polarizing microscope and the Brownian motion of a fluorescent particle trapped weakly by optical tweezers. The calculated cross-correlation function of the particle position and the spatial gradient of the intensity is nonzero, clearly indicating the existence of coupling.
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Affiliation(s)
- Hiroshi Orihara
- Division of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
| | - Nobutaka Sakurai
- Division of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
| | - Yuji Sasaki
- Division of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
| | - Tomoyuki Nagaya
- Department of Electrical and Electronic Engineering, Oita University, Oita 870-1192, Japan
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Škarabot M, Osterman N, Muševič I. Optothermally driven colloidal transport in a confined nematic liquid crystal. SOFT MATTER 2017; 13:2448-2452. [PMID: 28277573 DOI: 10.1039/c7sm00136c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate transport of microparticles by rapid movement of a laser spot in a thin layer of a nematic liquid crystal. The transport is achieved by fluid flow, caused by two different mechanisms. The thermoviscous expansion effect induces colloidal transport in the direction opposite to the laser movement, whereas thermally induced local melting of the liquid crystal pulls the particles in the direction of the laser movement. We demonstrate control of colloidal transport by changing the speed of the laser trap movement and the laser power. We anticipate that complex optofluidic colloidal transport could be realized in the nematic liquid crystal using a channel-free optofluidic approach.
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Affiliation(s)
- M Škarabot
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
| | - N Osterman
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia. and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
| | - I Muševič
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia. and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
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33
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Conklin C, Viñals J. Electrokinetic flows in liquid crystal thin films with fixed anchoring. SOFT MATTER 2017; 13:725-739. [PMID: 27973626 DOI: 10.1039/c6sm02393b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We study ionic and mass transport in a liquid crystalline fluid film in its nematic phase under an applied electrostatic field. Both analytic and numerical solutions are given for some prototypical configurations of interest in electrokinetics: thin films with spatially nonuniform nematic director that are either periodic or comprise a set of isolated disclinations. We present a quantitative description of the mechanisms inducing spatial charge separation in the nematic, and of the structure and magnitude of the resulting flows. The fundamental solutions for the charge distribution and flow velocities induced by disclinations of topological charge m = -1/2, 1/2 and 1 are given. These solutions allow the analysis of several designer flows, such as "pusher" flows created by three colinear disclinations, the flow induced by an immersed spherical particle (equivalent to an m = 1 defect) and its accompanying m = -1 hyperbolic hedgehog defect, and the mechanism behind nonlinear ionic mobilities when the imposed field is perpendicular to the line joining the defects.
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Affiliation(s)
- Christopher Conklin
- School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA.
| | - Jorge Viñals
- School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA.
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34
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Peng C, Turiv T, Zhang R, Guo Y, Shiyanovskii SV, Wei QH, de Pablo J, Lavrentovich OD. Controlling placement of nonspherical (boomerang) colloids in nematic cells with photopatterned director. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:014005. [PMID: 27830662 DOI: 10.1088/0953-8984/29/1/014005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Placing colloidal particles in predesigned sites represents a major challenge of the current state-of-the-art colloidal science. Nematic liquid crystals with spatially varying director patterns represent a promising approach to achieve a well-controlled placement of colloidal particles thanks to the elastic forces between the particles and the surrounding landscape of molecular orientation. Here we demonstrate how the spatially varying director field can be used to control placement of non-spherical particles of boomerang shape. The boomerang colloids create director distortions of a dipolar symmetry. When a boomerang particle is placed in a periodic splay-bend director pattern, it migrates towards the region of a maximum bend. The behavior is contrasted to that one of spherical particles with normal surface anchoring, which also produce dipolar director distortions, but prefer to compartmentalize into the regions with a maximum splay. The splay-bend periodic landscape thus allows one to spatially separate these two types of particles. By exploring overdamped dynamics of the colloids, we determine elastic driving forces responsible for the preferential placement. Control of colloidal locations through patterned molecular orientation can be explored for future applications in microfluidic, lab on a chip, sensing and sorting devices.
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Affiliation(s)
- Chenhui Peng
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA
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35
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Varney MCM, Zhang Q, Senyuk B, Smalyukh II. Self-assembly of colloidal particles in deformation landscapes of electrically driven layer undulations in cholesteric liquid crystals. Phys Rev E 2016; 94:042709. [PMID: 27841645 DOI: 10.1103/physreve.94.042709] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Indexed: 04/26/2023]
Abstract
We study elastic interactions between colloidal particles and deformation landscapes of undulations in a cholesteric liquid crystal under an electric field applied normal to cholesteric layers. The onset of undulation instability is influenced by the presence of colloidal inclusions and, in turn, layers' undulations mediate the spatial patterning of particle locations. We find that the bending of cholesteric layers around a colloidal particle surface prompts the local nucleation of an undulations lattice at electric fields below the well-defined threshold known for liquid crystals without inclusions, and that the onset of the resulting lattice is locally influenced, both dimensionally and orientationally, by the initial arrangements of colloids defined using laser tweezers. Spherical particles tend to spatially localize in the regions of strong distortions of the cholesteric layers, while colloidal nanowires exhibit an additional preference for multistable alignment offset along various vectors of the undulations lattice. Magnetic rotation of superparamagnetic colloidal particles couples with the locally distorted helical axis and undulating cholesteric layers in a manner that allows for a controlled three-dimensional translation of these particles. These interaction modes lend insight into the physics of liquid crystal structure-colloid elastic interactions, as well as point the way towards guided self-assembly of reconfigurable colloidal composites with potential applications in diffraction optics and photonics.
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Affiliation(s)
- Michael C M Varney
- Department of Physics and Soft Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Qiaoxuan Zhang
- Department of Physics and Soft Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA
- Materials Science and Engineering Program, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Bohdan Senyuk
- Department of Physics and Soft Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Ivan I Smalyukh
- Department of Physics and Soft Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA
- Materials Science and Engineering Program, University of Colorado at Boulder, Boulder, Colorado 80309, USA
- Department of Electrical, Computer, and Energy Engineering, University of Colorado at Boulder, Boulder, Colorado 80309, USA
- Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory and University of Colorado at Boulder, Boulder, Colorado 80309, USA
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36
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Peng C, Turiv T, Guo Y, Shiyanovskii SV, Wei QH, Lavrentovich OD. Control of colloidal placement by modulated molecular orientation in nematic cells. SCIENCE ADVANCES 2016; 2:e1600932. [PMID: 27652343 PMCID: PMC5026424 DOI: 10.1126/sciadv.1600932] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 08/11/2016] [Indexed: 05/25/2023]
Abstract
Colloids self-assemble into various organized superstructures determined by particle interactions. There is tremendous progress in both the scientific understanding and the applications of self-assemblies of single-type identical particles. Forming superstructures in which the colloidal particles occupy predesigned sites and remain in these sites despite thermal fluctuations represents a major challenge of the current state of the art. We propose a versatile approach to directing placement of colloids using nematic liquid crystals with spatially varying molecular orientation preimposed by substrate photoalignment. Colloidal particles in a nematic environment are subject to the long-range elastic forces originating in the orientational order of the nematic. Gradients of the orientational order create an elastic energy landscape that drives the colloids into locations with preferred type of deformations. As an example, we demonstrate that colloidal spheres with perpendicular surface anchoring are driven into the regions of maximum splay, whereas spheres with tangential surface anchoring settle into the regions of bend. Elastic forces responsible for preferential placement are measured by exploring overdamped dynamics of the colloids. Control of colloidal self-assembly through patterned molecular orientation opens new opportunities for designing materials and devices in which particles should be placed in predesigned locations.
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37
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Tamura Y, Kimura Y. Two-dimensional assemblies of nematic colloids in homeotropic cells and their response to electric fields. SOFT MATTER 2016; 12:6817-6826. [PMID: 27453568 DOI: 10.1039/c6sm00929h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Micrometer-sized colloidal particles dispersed in nematic liquid crystals interact with each other through anisotropic interactions induced by orientational deformation of the nematic field. In the case of so-called dipole nematic colloids, their interaction is of the dipole-dipole type. Two-dimensional, non-close-packed colloidal assemblies having various characteristics were fabricated using optical tweezers by exploiting the attraction between anti-parallel dipole nematic colloids in homeotropically aligned nematic cells. Structures comprising polygons, squares, and tetrahedra were built using equal-sized particles, and hexagonal structures were built using particles of two sizes. As the nematic field is sensitive to electric fields, the response of the fabricated assemblies toward an alternating electric field was also studied. All assemblies exhibited homogeneous reversible shrinkage, and their shrinkage rates were dependent on the structure. The maximum shrinkage rate in the linear dimension of the assemblies was over 20% at 5 Vrms for a hexagon comprising tetrahedral units.
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Affiliation(s)
- Yuta Tamura
- Department of Physics, School of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
| | - Yasuyuki Kimura
- Department of Physics, School of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
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39
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Alama S, Bronsard L, Lamy X. Analytical description of the Saturn-ring defect in nematic colloids. Phys Rev E 2016; 93:012705. [PMID: 26871133 DOI: 10.1103/physreve.93.012705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Indexed: 06/05/2023]
Abstract
We derive an analytical formula for the Saturn-ring configuration around a small colloidal particle suspended in nematic liquid crystal. In particular we obtain an explicit expression for the ring radius and its dependence on the anchoring energy. We work within Landau-de Gennes theory: Nematic alignment is described by a tensorial order parameter. For nematic colloids this model had previously been used exclusively to perform numerical computations. Our method demonstrates that the tensorial theory can also be used to obtain analytical results, suggesting a different approach to the understanding of nematic colloidal interactions.
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Affiliation(s)
- Stan Alama
- Department of Mathematics and Statistics, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1
| | - Lia Bronsard
- Department of Mathematics and Statistics, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1
| | - Xavier Lamy
- Institut Camille Jordan, Université Lyon 1, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France and Max-Planck Institut, Inselstrasse 22, 04103 Leipzig, Germany
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40
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Chakraborty S, Nelson N, Schwartz DK. Anisotropic molecular hopping at the solid-nematic interface. SOFT MATTER 2015; 11:7712-7716. [PMID: 26313353 DOI: 10.1039/c5sm01251a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Single molecule tracking was used to observe intermittent and anisotropic molecular motion at the solid-nematic interface. Although the interfacial diffusion was dramatically slower than self-diffusion in the nematic, the diffusion anisotropy was the same at the interface and in bulk, supporting the desorption-mediated mechanism of interfacial diffusion, where molecules sample the physical properties of the vicinal fluid phase during flights, and the magnitude of the interfacial diffusion coefficient is primarily determined by the distribution of waiting times between flights.
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Affiliation(s)
- Saonti Chakraborty
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80309, USA.
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41
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Chen K, Metcalf LP, Rivas DP, Reich DH, Leheny RL. Anisotropic colloidal transport and periodic stick-slip motion in cholesteric finger textures. SOFT MATTER 2015; 11:4189-4196. [PMID: 25875803 DOI: 10.1039/c5sm00300h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have investigated the mobility of discoidal colloidal particles sedimenting within cholesteric finger textures formed by mixtures of the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) and the chiral dopant 4-(2-methylbutyl)-4'-cyanobiphenyl (CB15) with cholesteric pitch p between 24 and 114 μm. The nickel disks, with radius 17 μm and thickness 300 nm, displayed varied transport behavior that depended on the size of the pitch and the orientation of the gravitational force with respect to the cholesteric axis. In textures with small pitch (p < 40 μm), the disks moved perpendicular to the axis irrespective of the orientation of gravity as a result of an elastic retarding force that prevented motion along the axis. In textures with larger pitch, the disks similarly moved perpendicular to the axis when the angle between the force and axis was large. When the angle was small, the disks displayed stick-slip motion caused by periodic yielding of the finger texture. A model considering viscous drag on the particles and the elastic energy cost of deforming the finger texture describes the stick-slip motion accurately. The effective drag viscosities obtained from the disk motion are anomalously large compared with those of pure nematic 5CB indicating a large contribution to the dissipation from the motion of disclinations in the texture in the vicinity of the translating disks.
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Affiliation(s)
- Kui Chen
- Department of Physics & Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
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42
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Sasaki Y, Hoshikawa H, Seto T, Kobayashi F, Jampani VSR, Herminghaus S, Bahr C, Orihara H. Direct visualization of spatiotemporal structure of self-assembled colloidal particles in electrohydrodynamic flow of a nematic liquid crystal. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:3815-3819. [PMID: 25774695 DOI: 10.1021/acs.langmuir.5b00450] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Characterization of spatiotemporal dynamics is of vital importance to soft matter systems far from equilibrium. Using a confocal laser scanning microscopy, we directly reveal three-dimensional motion of surface-modified particles in the electrohydrodynamic convection of a nematic liquid crystal. Particularly, visualizing a caterpillar-like motion of a self-assembled colloidal chain demonstrates the mechanism of the persistent transport enabled by the elastic, electric, and hydrodynamic contributions. We also precisely show how the particles' trajectory is spatially modified by simply changing the surface boundary condition.
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Affiliation(s)
- Yuji Sasaki
- †Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Hikaru Hoshikawa
- †Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Takafumi Seto
- †Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Fumiaki Kobayashi
- †Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - V S R Jampani
- ‡Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Göttingen, Germany
| | - Stephan Herminghaus
- ‡Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Göttingen, Germany
| | - Christian Bahr
- ‡Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Göttingen, Germany
| | - Hiroshi Orihara
- †Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
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Chakrabarti A, Chaudhury MK. Attraction of mesoscale objects on the surface of a thin elastic film supported on a liquid. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:1911-1920. [PMID: 25069091 DOI: 10.1021/la502236r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We study the interaction of two parallel rigid cylinders on the surface of a thin elastic film supported on a pool of liquid. The excess energy of the surface due to the curvature of the stretched film induces attraction of the cylinders that can be quantified by the variation of their gravitational potential energies as they descend into the liquid while still floating on the film. Although the experimental results follow the trend predicted from the balance of the gravitational and elastic energies of the system, they are somewhat underestimated. The origin of this discrepancy is the hysteresis of adhesion between the cylinder and the elastic film that does not allow the conversion of the total available energy into gravitational potential energy, as some part of it is recovered in stretching the film behind the cylinders while they approach each other. A modification of the model accounting for the effects of adhesion hysteresis improves the agreement between theoretical and experimental results. The contribution of the adhesion hysteresis can be reduced considerably by introducing a thin hydrogel layer atop the elastic film that enhances the range of attraction of the cylinders (as well as rigid spheres) in a dramatic way. Morphological instabilities in the gel project corrugated paths to the motion of small spheres, thus leading to a large numbers of particles to aggregate along their defects. These observations suggest that a thin hydrogel layer supported on a deformable elastic film affords an effective model system to study elasticity and defects mediated interaction of particles on its surface.
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Affiliation(s)
- Aditi Chakrabarti
- Department of Chemical Engineering Lehigh University , Bethlehem, Pennsylvania 18015, United States
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44
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Pergamenshchik VM. Elastic multipoles in the field of the nematic director distortions. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2014; 37:121. [PMID: 25471929 DOI: 10.1140/epje/i2014-14121-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 09/29/2014] [Accepted: 10/14/2014] [Indexed: 06/04/2023]
Abstract
Theory of the interaction between all types of elastic dipoles and quadrupoles and distortions of the nematic director is presented. If a particle is small relative to the characteristic distortion length, the interaction is determined by the director derivatives at the particle location. We consider a spherical particle since, even under the standard assumptions of the multipole theory (weak deformations, one constant approximation), the problem can be solved analytically only in this case. Different dipoles interact with different distortion modes (e.g., isotropic dipole interacts with the splay, chiral dipole with the twist, and so on). In the main order, the interaction of a dipole is linear in the director derivatives, and the interaction of a quadrupole is linear in the second-order director derivatives. The theory goes beyond the main-order terms and predicts an effective distortion-induced dipolar component on a particle. This effect is described by the free energy term quadratic in the director derivatives and has contributions both of a bulk and surface origin. The bulk effect takes place even if the director at the particle surface is fixed, whereas the surface effect appears if the surface director is perturbed by the distortions due to a weak surface anchoring. The theory is illustrated by simple examples of the interaction of elastic dipoles with a disclination line, with cholesteric spiral, and with the director distortions in a hybrid cell.
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45
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Varney MCM, Zhang Q, Tasinkevych M, Silvestre NM, Bertness KA, Smalyukh II. Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:062502. [PMID: 25615114 DOI: 10.1103/physreve.90.062502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Indexed: 06/04/2023]
Abstract
Nematic and cholesteric liquid crystals are three-dimensional fluids that possess long-range orientational ordering and can support both topological defects and chiral superstructures. Implications of this ordering remain unexplored even for simple dynamic processes such as the ones found in so-called "fall experiments," or motion of a spherical inclusion under the effects of gravity. Here we show that elastic and surface anchoring interactions prompt periodic dynamics of colloidal microparticles in confined cholesterics when gravity acts along the helical axis. We explore elastic interactions between colloidal microparticles and confining surfaces as well as with an aligned ground-state helical structure of cholesterics for different sizes of spheres relative to the cholesteric pitch, demonstrating unexpected departures from Stokes-like behavior at very low Reynolds numbers. We characterize metastable localization of microspheres under the effects of elastic and surface anchoring periodic potential landscapes seen by moving spheres, demonstrating the important roles played by anchoring memory, confinement, and topological defect transformation. These experimental findings are consistent with the results of numerical modeling performed through minimizing the total free energy due to colloidal inclusions at different locations along the helical axis and with respect to the confining substrates. A potential application emerging from this work is colloidal sorting based on particle shapes and sizes.
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Affiliation(s)
- Michael C M Varney
- Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Qiaoxuan Zhang
- Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA and Materials Science and Engineering Program, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Mykola Tasinkevych
- Max-Planck-Institut für Intelligente Systeme, D-70569 Stuttgart, Germany and Institut für Theoretische Physik IV, Universität Stuttgart, D-70569 Stuttgart, Germany
| | - Nuno M Silvestre
- Centro de Física Teórica e Computacional and Faculdade de Ciências da Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal
| | - Kris A Bertness
- National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Ivan I Smalyukh
- Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA and Materials Science and Engineering Program, University of Colorado at Boulder, Boulder, Colorado 80309, USA and Department of Electrical, Computer, and Energy Engineering and Liquid Crystals Materials Research Center, University of Colorado at Boulder, Boulder, Colorado 80309, USA and Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory and University of Colorado at Boulder, Boulder, Colorado 80309, USA
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46
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Sasaki Y, Takikawa Y, Jampani VSR, Hoshikawa H, Seto T, Bahr C, Herminghaus S, Hidaka Y, Orihara H. Colloidal caterpillars for cargo transportation. SOFT MATTER 2014; 10:8813-8820. [PMID: 25220483 DOI: 10.1039/c4sm01354a] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Tunable transport of tiny objects in fluid systems is demanding in diverse fields of science such as drug delivery, active matter far from equilibrium, and lab-on-a-chip applications. Here, we report the directed motion of colloidal particles and self-assembled colloidal chains in a nematic liquid crystal matrix using electrohydrodynamic convection (EHC) rolls. The asymmetric distortion of the molecular orientation around the particles results - for single particles - in a hopping motion from one EHC roll to the next and - for colloidal chains - in a caterpillar-like motion in the direction perpendicular to the roll axes. We demonstrate the use of colloidal chains as microtraction engines for the transport of various types of microcargo.
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Affiliation(s)
- Yuji Sasaki
- Division of Applied Physics, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
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47
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Senyuk B, Varney MCM, Lopez JA, Wang S, Wu N, Smalyukh II. Magnetically responsive gourd-shaped colloidal particles in cholesteric liquid crystals. SOFT MATTER 2014; 10:6014-6023. [PMID: 24994521 DOI: 10.1039/c4sm00878b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Particle shape and medium chirality are two key features recently used to control anisotropic colloidal self-assembly and dynamics in liquid crystals. Here, we study magnetically responsive gourd-shaped colloidal particles dispersed in cholesteric liquid crystals with periodicity comparable or smaller than the particle's dimensions. Using magnetic manipulation and optical tweezers, which allow one to position colloids near the confining walls, we measured the elastic repulsive interactions of these particles with confining surfaces and found that separation-dependent particle-wall interaction force is a non-monotonic function of separation and shows oscillatory behavior. We show that gourd-shaped particles in cholesterics reside not on a single sedimentation level, but on multiple long-lived metastable levels separated by a distance comparable to cholesteric periodicity. Finally, we demonstrate three-dimensional laser tweezers assisted assembly of gourd-shaped particles taking advantage of both orientational order and twist periodicity of cholesterics, potentially allowing new forms of orientationally and positionally ordered colloidal organization in these media.
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Affiliation(s)
- Bohdan Senyuk
- Department of Physics, University of Colorado, Boulder, CO 80309, USA.
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48
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Hirankittiwong P, Chattham N, Limtrakul J, Haba O, Yonetake K, Eremin A, Stannarius R, Takezoe H. Optical manipulation of the nematic director field around microspheres covered with an azo-dendrimer monolayer. OPTICS EXPRESS 2014; 22:20087-20093. [PMID: 25321218 DOI: 10.1364/oe.22.020087] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report here the optical manipulation of the director and topological defect structures of nematic liquid crystals around a silica microparticle with azobenzene-containing dendrimers (azo-dendrimers) on its surface. We successfully demonstrate the successive switching processes from hedgehog, to boojum, and further to Saturn ring configurations by ultraviolet (UV) light irradiation and termination. The switching time between these defect structures depends on the UV light intensity and attains about 50 ms. Since the pretreatment of microparticles is not necessary and the surface modification is spontaneously performed just by dissolving the azo-dendrimers in liquid crystals, this dendrimer supplies us with a variety of possible applications.
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49
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Hsu CJ, Kuo CC, Hsieh CD, Huang CY. Effects of silica nanoparticles on electro-optical properties of polymer-stabilized liquid crystals. OPTICS EXPRESS 2014; 22:18513-18518. [PMID: 25089470 DOI: 10.1364/oe.22.018513] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We control the pretilt angle of liquid crystals (LCs) by simultaneously doping silica nanoparticles (SNs) and reactive monomers into the LC cell. Application of AC high voltage (ACHV) to the cell compels the lifting force and the facilitation of polar groups to move the SNs and monomers toward the substrate surface. Polymer networks and SNs are stabilized at the substrate surface after UV exposure, sustaining the LCs at high pretilt angles. The deposited SNs on the substrate surface increases the anchoring energy of the substrate; the dispersed SNs in the cell decrease the relaxation constant of LCs. Therefore, the response time of the high-pretilted-polymer-stabilized LC cell is decreased. The method enables the control of the LC pretilt angle over a broad range. The slow response time of the polymer-stabilized LC cell from high monomer dose can also be prevented following the addition of SNs.
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Chakrabarti A, Chaudhury MK. Elastocapillary interaction of particles on the surfaces of ultrasoft gels: a novel route to study self-assembly and soft lubrication. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:4684-4693. [PMID: 24702043 DOI: 10.1021/la5007988] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We study the interaction of small hydrophobic particles on the surface of an ultrasoft elastic gel, in which a small amount of elasticity of the medium balances the weights of the particles. The excess energy of the surface of the deformed gel causes them to attract as is the case with the generic capillary interactions of particles on a liquid surface. The variation of the gravitational potential energies of the particles resulting from their descents in the gel coupled with the superposition principle of Nicolson allow a fair estimation of the distance dependent attractive energy of the particles. This energy follows a modified Bessel function of the second kind with a characteristic elastocapillary decay length that decreases with the elasticity of the medium. An interesting finding of this study is that the particles on the gel move toward each other as if the system possesses a negative diffusivity that is inversely proportional to friction. This study illustrates how the capillary interaction of particles is modified by the elasticity of the medium, which is expected to have important implications in the surface force driven self-assembly of particles. In particular, this study points out that the range and the strength of the capillary interaction can be tuned in by appropriate choices of the elasticity of the support and the interfacial tension of the surrounding medium. Manipulation of the particle interactions is exemplified in such fascinating mimicry of the biological processes as the tubulation and phagocytic engulfment and in the assembly of particles that can be used to study nucleation and clustering phenomena in well-controlled settings.
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Affiliation(s)
- Aditi Chakrabarti
- Department of Chemical Engineering Lehigh University , Bethlehem, Pennsylvania 18015, United States
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