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Safdari M, Zandi R, van der Schoot P. Dynamics of elongation of nematic tactoids in an electric field. Phys Rev E 2024; 109:054706. [PMID: 38907476 DOI: 10.1103/physreve.109.054706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2023] [Accepted: 04/22/2024] [Indexed: 06/24/2024]
Abstract
Nematic tactoids are spindle-shaped droplets of a nematic phase nucleated in the co-existing isotropic phase. According to equilibrium theory, their internal structure and shape are controlled by a balance between the elastic deformation of the director field, induced by the preferred anchoring of that director field to the interface, and the interfacial free energy. Recent experiments on tactoids of chitin nanocrystals dispersed in water show that electrical fields can very strongly elongate tactoids, at least if the tactoids are sufficiently large in volume. However, this observation contradicts the predictions of equilibrium theory as well as findings from Monte Carlo simulations that do not show this kind of extreme elongation to take place at all. To explain this, we put forward a relaxational model based on the Oseen-Frank free energy of elastic deformation of a director field coupled to an anisotropic surface free energy. In our model, we use two reaction coordinates to describe the director field and the extent of elongation of the droplets and evaluate the evolution of both as a function of time following the switching on of an electric field. Depending on the relative magnitude of the fundamental relaxation rates associated with the two reaction coordinates, we find that the aspect ratio of the drops may develop a large and very long-lived overshoot before eventually relaxing to the much smaller equilibrium value. In that case, the response of the curvature of the director field lags behind, explaining the experimental observations. Our theory describes the experimental data reasonably well.
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2
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Kuhnhold A, van der Schoot P. Structure of nematic tactoids of hard rods. J Chem Phys 2022; 156:104501. [DOI: 10.1063/5.0078056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study by means of Monte Carlo simulations the internal structure of nematic droplets or tactoids formed by hard, rod-like particles in a gas of spherical ghost particles that act as depletion agents for the rods. We find that the shape and internal structure of tactoids are strongly affected by the size of the droplets. The monotonically increasing degree of nematic order with increasing particle density that characterizes the bulk nematic phase is locally violated and more so the smaller the tactoid. We also investigate the impact of an external quadrupolar alignment field on tactoids and find that this tends to make the director field more uniform, but not to very significantly increase the tactoid’s aspect ratio. This agrees with recent theoretical predictions yet is at variance with experimental observations and dynamical simulations. We explain this discrepancy in terms of competing relaxation times.
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Affiliation(s)
- Anja Kuhnhold
- Institute of Physics, University of Freiburg, 79104 Freiburg (Breisgau), Germany
| | - Paul van der Schoot
- Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
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3
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Submersed micropatterned structures control active nematic flow, topology, and concentration. Proc Natl Acad Sci U S A 2021; 118:2106038118. [PMID: 34535551 DOI: 10.1073/pnas.2106038118] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/24/2021] [Indexed: 01/10/2023] Open
Abstract
Coupling between flows and material properties imbues rheological matter with its wide-ranging applicability, hence the excitement for harnessing the rheology of active fluids for which internal structure and continuous energy injection lead to spontaneous flows and complex, out-of-equilibrium dynamics. We propose and demonstrate a convenient, highly tunable method for controlling flow, topology, and composition within active films. Our approach establishes rheological coupling via the indirect presence of fully submersed micropatterned structures within a thin, underlying oil layer. Simulations reveal that micropatterned structures produce effective virtual boundaries within the superjacent active nematic film due to differences in viscous dissipation as a function of depth. This accessible method of applying position-dependent, effective dissipation to the active films presents a nonintrusive pathway for engineering active microfluidic systems.
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Optical Microscopy Observations and Construction of Dupin Cyclides at the Isotropic/Smectic A Phase Transition. MATERIALS 2021; 14:ma14164539. [PMID: 34443061 PMCID: PMC8398811 DOI: 10.3390/ma14164539] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 08/08/2021] [Accepted: 08/09/2021] [Indexed: 11/26/2022]
Abstract
In this work, we are interested in the nucleation of bâtonnets at the Isotropic/Smectic A phase transition of 10CB liquid crystal. Very often, these bâtonnets are decorated with a large number of focal conics. We present here an example of a bâtonnet obtained by optical crossed polarized microscopy in a frequently observed particular area of the sample. This bâtonnet presents bulges and one of them consists of a tessellation of ellipses. These ellipses are two by two tangent, one to each other, and their confocal hyperbolas merge at the apex of the bâtonnet. We propose a numerical simulation with Python software to reproduce this tiling of ellipses as well as the shape of the smectic layers taking the well-known shape of Dupin cyclides within this particular bâtonnet area.
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Ansell HS, Kamien RD. Twisted loxodromes in spindle-shaped polymer nematics. SOFT MATTER 2021; 17:7076-7085. [PMID: 34235531 DOI: 10.1039/d1sm00772f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We develop an energetic model that captures the twisting behavior of spindle-shaped polymer microparticles with nematic ordering, which display remarkably different twisting behavior to ordinary nematics confined to spindles. We have previously developed a geometric model of the twisting, based on experimental observations, in which we showed that the twist pattern follows loxodrome spirals [Ansell, et al., Phys. Rev. Lett., 2019, 123, 157801]. In this study, we first consider a spindle-shaped surface and show that the loxodrome twisting behavior of our system can be captured by the Frank free energy of the nematic with an additional term constraining the length of the integral curves of the system. We then extend the ideas of this model to the bulk and explore the parameter space for which the twisted loxodrome solution is energetically favorable.
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Affiliation(s)
- Helen S Ansell
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
| | - Randall D Kamien
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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Safdari M, Zandi R, van der Schoot P. Effect of electric fields on the director field and shape of nematic tactoids. Phys Rev E 2021; 103:062703. [PMID: 34271629 DOI: 10.1103/physreve.103.062703] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Accepted: 04/06/2021] [Indexed: 01/30/2023]
Abstract
Tactoids are spindle-shaped droplets of a uniaxial nematic phase suspended in the coexisting isotropic phase. They are found in dispersions of a wide variety of elongated colloidal particles, including actin, fd virus, carbon nanotubes, vanadium peroxide, and chitin nanocrystals. Recent experiments on tactoids of chitin nanocrystals in water show that electric fields can very strongly elongate tactoids even though the dielectric properties of the coexisting isotropic and nematic phases differ only subtly. We develop a model for partially bipolar tactoids, where the degree of bipolarness of the director field is free to adjust to optimize the sum of the elastic, surface, and Coulomb energies of the system. By means of a combination of a scaling analysis and a numerical study, we investigate the elongation and director field's behavior of the tactoids as a function of their size, the strength of the electric field, the surface tension, anchoring strength, the elastic constants, and the electric susceptibility anisotropy. We find that tactoids cannot elongate significantly due to an external electric field, unless the director field is bipolar or quasibipolar and somehow frozen in the field-free configuration. Presuming that this is the case, we find reasonable agreement with experimental data.
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Affiliation(s)
- Mohammadamin Safdari
- Department of Physics, University of California, Riverside, California 92521, USA
| | - Roya Zandi
- Department of Physics, University of California, Riverside, California 92521, USA
| | - Paul van der Schoot
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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7
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Qiu M, Feng JJ, Loudet JC. Phase-field model for elastocapillary flows of liquid crystals. Phys Rev E 2021; 103:022706. [PMID: 33736098 DOI: 10.1103/physreve.103.022706] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 01/19/2021] [Indexed: 11/07/2022]
Abstract
We propose a phase-field model to study interfacial flows of nematic liquid crystals that couple the capillary forces on the interface with the elastic stresses in the nematic phase. The theoretical model has two key ingredients: A tensor order parameter that provides a consistent description of the molecular and distortional elasticity, and a phase-field formalism that accurately represents the interfacial tension and the nematic anchoring stress by approximating a sharp-interface limit. Using this model, we carry out finite-element simulations of drop retraction in a surrounding fluid, with either component being nematic. The results are summarized by eight representative steady-state solutions in planar and axisymmetric geometries, each featuring a distinct configuration for the drop and the defects. The dynamics is dominated by the competition between the interfacial tension and the distortional elasticity in the nematic phase, mediated by the anchoring condition on the drop surface. As consequences of this competition, the steady-state drop deformation and the clearance between the defects and the drop surface both depend linearly on the elastocapillary number.
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Affiliation(s)
- Mingfeng Qiu
- Department of Mathematics, University of British Columbia, Vancouver, British Columbia V6T 1Z2, Canada
| | - James J Feng
- Department of Mathematics and Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z2, Canada
| | - Jean-Christophe Loudet
- Université de Bordeaux, CNRS, Centre de Recherche Paul Pascal (UMR 5031), F-33600 Pessac, France
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Qu D, Zussman E. Electro-responsive Liquid Crystalline Nanocelluloses with Reversible Switching. J Phys Chem Lett 2020; 11:6697-6703. [PMID: 32787220 DOI: 10.1021/acs.jpclett.0c01924] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Liquid crystalline cellulose nanocrystals (CNCs) which can change their structural and optical properties in an electric field could be a new choice for advanced optoelectronic devices. Unfortunately, the exploration of its performance in an electric field is underdeveloped. Hence, we reveal some interesting dielectric coupling activities of liquid crystalline CNC in an electric field. The CNC tactoid is shown to orient its helix axis normal to the electric field direction. Then, as a function of the electric field strength and frequency, the tactoid can be stretched along with a pitch increase, with a deformation mechanism significantly differing at varied frequencies, and finally untwists the helix axis to form a nematic structure upon increasing the electric field strength. Moreover, a straightforward method to visualize the electric field is demonstrated, by combining the CNC uniform lying helix textures with polarized optical microscopy. We envision these understandings could facilitate the development of liquid crystalline CNC in the design of electro-optical devices.
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Affiliation(s)
- Dan Qu
- Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel
| | - Eyal Zussman
- Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel
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Ludwig NB, Weirch KL, Alster E, Witten TA, Gardel ML, Dasbiswas K, Vaikuntanathan S. Nucleation and shape dynamics of model nematic tactoids around adhesive colloids. J Chem Phys 2020; 152:084901. [PMID: 32113348 DOI: 10.1063/1.5141997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Recent experiments have shown how nematically ordered tactoid shaped actin droplets can be reorganized and divided by the action of myosin molecular motors. In this paper, we consider how similar morphological changes can potentially be achieved under equilibrium conditions. Using simulations, both atomistic and continuum, and a simple macroscopic model, we explore how the nucleation dynamics, shape changes, and the final steady state of a nematic tactoid droplet can be modified by interactions with model adhesive colloids that mimic a myosin motor cluster. We show how tactoid reorganization may occur in an equilibrium colloidal-nematic setting. We then suggest based on the simple macroscopic model how the simulation models may be extended to potentially stabilize divided tactoids.
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Affiliation(s)
- Nicholas B Ludwig
- Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Kimberly L Weirch
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, USA
| | - Eli Alster
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Thomas A Witten
- Department of Physics and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Margaret L Gardel
- Department of Physics and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Kinjal Dasbiswas
- Department of Physics, University of California, Merced, Merced, California 95343, USA
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10
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Shi W, Chen X, Li B, Weitz DA. Spontaneous Creation of Anisotropic Polymer Crystals with Orientation-Sensitive Birefringence in Liquid Drops. ACS APPLIED MATERIALS & INTERFACES 2020; 12:3912-3918. [PMID: 31909961 DOI: 10.1021/acsami.9b17308] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
It remains a grand challenge to prepare anisotropic crystal superstructures with sensitive optical properties in polymer science and materials field. This study demonstrates that semicrystalline polymers develop into anisotropic hollow spherulitic crystals spontaneously at interfaces of liquid drops. In contrast to conventional spherulites with centrosymmetric optics and grain boundaries, these anisotropic spherulitic crystals have vanished boundary defects, tunable aspect ratios, and noncentrosymmetric, orientation-sensitive birefringence. The experimental finding is elaborated in poly(l-lactic acid) crystals and is further verified in a broad class of semicrystalline polymers, irrespective of molecular chirality, chemical constitution, or interfacial modification. The facile methods and general mechanism revealed in this study shed light on developing new types of optical microdevices and synthesis of anisotropic semicrystalline particles from liquid emulsions.
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Affiliation(s)
- Weichao Shi
- Key Laboratory of Functional Polymer Materials (Ministry of Education) , Nankai University , Tianjin 300071 , China
- Institute of Polymer Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Xiaotong Chen
- Key Laboratory of Functional Polymer Materials (Ministry of Education) , Nankai University , Tianjin 300071 , China
- Institute of Polymer Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Baihui Li
- Key Laboratory of Functional Polymer Materials (Ministry of Education) , Nankai University , Tianjin 300071 , China
- Institute of Polymer Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - David A Weitz
- John A. Paulson School of Engineering and Applied Sciences , Harvard University , Cambridge , Massachusetts 02138 , United States
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11
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Metselaar L, Yeomans JM, Doostmohammadi A. Topology and Morphology of Self-Deforming Active Shells. PHYSICAL REVIEW LETTERS 2019; 123:208001. [PMID: 31809098 DOI: 10.1103/physrevlett.123.208001] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Indexed: 06/10/2023]
Abstract
We present a generic framework for modeling three-dimensional deformable shells of active matter that captures the orientational dynamics of the active particles and hydrodynamic interactions on the shell and with the surrounding environment. We find that the cross talk between the self-induced flows of active particles and dynamic reshaping of the shell can result in conformations that are tunable by varying the form and magnitude of active stresses. We further demonstrate and explain how self-induced topological defects in the active layer can direct the morphodynamics of the shell. These findings are relevant to understanding morphological changes during organ development and the design of bioinspired materials that are capable of self-organization.
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Affiliation(s)
- Luuk Metselaar
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Julia M Yeomans
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Amin Doostmohammadi
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
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12
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O'Keeffe O, Wang PX, Hamad WY, MacLachlan MJ. Boundary Geometry Effects on the Coalescence of Liquid Crystalline Tactoids and Formation of Topological Defects. J Phys Chem Lett 2019; 10:278-282. [PMID: 30615453 DOI: 10.1021/acs.jpclett.8b03733] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
In many lyotropic liquid crystals, the evolution of macroscopic anisotropic phases is mediated by tactoids, which are discrete ordered microdroplets existing in continuous disordered phases. Here we report the effects of boundary conditions on the movement and transformation of liquid crystalline tactoids of cellulose nanocrystals (CNCs) in nonspherical droplets. Using an in situ photopolymerization method, we obtained three-dimensional views of the initial emergence and expansion of macroscopic ordered phases. These processes, as well as the evolution of topological defects, were significantly influenced by the boundary geometry (or Marangoni flows and pinning effects) of the droplets. This phenomenon helps explain the influence of the substrate on the photonic properties of chiral nematic films of CNCs and may also provide new insights into the self-assembly process in lyotropic liquid crystals.
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Affiliation(s)
- Orla O'Keeffe
- Department of Chemistry , University of British Columbia , 2036 Main Mall , Vancouver , British Columbia , Canada V6T 1Z1
| | - Pei-Xi Wang
- Department of Chemistry , University of British Columbia , 2036 Main Mall , Vancouver , British Columbia , Canada V6T 1Z1
| | - Wadood Y Hamad
- FPInnovations , 2665 East Mall , Vancouver , British Columbia , Canada V6T 1Z4
| | - Mark J MacLachlan
- Department of Chemistry , University of British Columbia , 2036 Main Mall , Vancouver , British Columbia , Canada V6T 1Z1
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13
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Affiliation(s)
- Luuk Metselaar
- The Rudolf Peierls Centre for Theoretical Physics, Clarendon Laboratory, Oxford, UK
| | - Amin Doostmohammadi
- The Rudolf Peierls Centre for Theoretical Physics, Clarendon Laboratory, Oxford, UK
| | - Julia M. Yeomans
- The Rudolf Peierls Centre for Theoretical Physics, Clarendon Laboratory, Oxford, UK
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Wang PX, Hamad WY, MacLachlan MJ. Size-Selective Exclusion Effects of Liquid Crystalline Tactoids on Nanoparticles: A Separation Method. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201712158] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Pei-Xi Wang
- Department of Chemistry; University of British Columbia; 2036 Main Mall Vancouver, British Columbia V6T 1Z1 Canada
| | - Wadood Y. Hamad
- FPInnovations; 2665 East Mall Vancouver British Columbia V6T 1Z4 Canada
| | - Mark J. MacLachlan
- Department of Chemistry; University of British Columbia; 2036 Main Mall Vancouver, British Columbia V6T 1Z1 Canada
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15
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Wang PX, Hamad WY, MacLachlan MJ. Size-Selective Exclusion Effects of Liquid Crystalline Tactoids on Nanoparticles: A Separation Method. Angew Chem Int Ed Engl 2018; 57:3360-3365. [DOI: 10.1002/anie.201712158] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 01/19/2018] [Indexed: 12/29/2022]
Affiliation(s)
- Pei-Xi Wang
- Department of Chemistry; University of British Columbia; 2036 Main Mall Vancouver, British Columbia V6T 1Z1 Canada
| | - Wadood Y. Hamad
- FPInnovations; 2665 East Mall Vancouver British Columbia V6T 1Z4 Canada
| | - Mark J. MacLachlan
- Department of Chemistry; University of British Columbia; 2036 Main Mall Vancouver, British Columbia V6T 1Z1 Canada
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