1
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Ettinger S, Slaughter CG, Parra SH, Kikkawa JM, Collings PJ, Yodh AG. Magnetic-field-driven director configuration transitions in radial nematic liquid crystal droplets. Phys Rev E 2023; 108:024704. [PMID: 37723717 DOI: 10.1103/physreve.108.024704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 07/21/2023] [Indexed: 09/20/2023]
Abstract
We study the director configurations of nematic liquid crystal (NLC) droplets with homeotropic anchoring in a magnetic field and report observation of a magnetic-field-driven transition from a deformed radial to an axial-with-defect configuration. Magnetic-field-induced transitions in NLC droplets differ fundamentally from the traditional planar Freedericksz transition due to the spherical droplet geometry and resulting topological defect. This transition has been studied theoretically, but the director configurations and mechanism of defect evolution in an applied magnetic field have yet to be observed experimentally. To this end, we combine polarized optical microscopy with a variable electromagnet (≤1 T) for continuous observation of droplet director fields, and we employ Landau-de Gennes numerical simulations to elucidate the director configurations and first-order nature of the transition. We report a configuration transition from point defect to ring defect at a critical field, which varies inversely with droplet radius and is relatively independent of surfactant type and concentration. We also estimate anchoring strengths of commonly used surfactants at the NLC-aqueous interface.
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Affiliation(s)
- Sophie Ettinger
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Charlotte G Slaughter
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Sebastian Hurtado Parra
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - James M Kikkawa
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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2
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Yang S, Zhang B, Murdock SR, Collings PJ. Orientational order of dyes in a lyotropic chromonic liquid crystal. Soft Matter 2022; 18:7415-7421. [PMID: 36129321 DOI: 10.1039/d2sm01110g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Absorption measurements allow the orientational order parameter of four dyes in the lyotropic chromonic liquid crystal di-sodium cromoglycate (DSCG) to be determined. The dye order parameters are small, except for dyes that intercalate between the DSCG molecules of the rod-like assemblies. The dye order parameters decrease with increasing temperature faster than the nematic order parameter of the DSCG assemblies. For intercalating dyes, the measured dye order parameter varies with the wavelength of the measurement because both intercalated and non-intercalated dye molecules contribute. On the contrary, measurements of the dye order parameter using fluorescence are sensitive only to intercalated dye molecules and produce values that reflect the order parameter of the DSCG assemblies. Therefore, the temperature and concentration dependence of the DSCG order parameter is also explored, since data of this kind on this often-studied system are lacking. Finally, the association constant of one of the intercalating dyes with the DSCG assemblies is determined, yielding a value considerably less than what is found for the same dye with DNA.
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Affiliation(s)
- S Yang
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA.
| | - Bingru Zhang
- Department of Physical Chemistry, University of Paderborn, Paderborn, Germany
| | - Solomon R Murdock
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA.
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA.
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
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3
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Wei WS, Jeong J, Collings PJ, Yodh AG. Focal conic flowers, dislocation rings, and undulation textures in smectic liquid crystal Janus droplets. Soft Matter 2022; 18:4360-4371. [PMID: 35608219 DOI: 10.1039/d1sm01623g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Liquid crystalline phases of matter often exhibit visually stunning patterns or textures. Mostly, these liquid crystal (LC) configurations are uniquely determined by bulk LC elasticity, surface anchoring conditions, and confinement geometry. Here, we experimentally explore defect textures of the smectic LC phase in unique confining geometries with variable curvature. We show that a complex range of director configurations can arise from a single system, depending on sample processing procedures. Specifically, we report on LC textures in Janus drops comprised of silicone oil and 8CB in its smectic-A LC phase. The Janus droplets were made in aqueous suspension using solvent-induced phase separation. After drop creation, smectic layers form in the LC compartment, but their self-assembly is frustrated by the need to accommodate both the bowl-shaped cavity geometry and homeotropic (perpendicular) anchoring conditions at boundaries. A variety of stable and metastable smectic textures arise, including focal conic domains, dislocation rings, and undulations. We experimentally characterize their stabilities and follow their spatiotemporal evolution. Overall, a range of fabrication kinetics produce very different intermediate and final states. The observations elucidate assembly mechanisms and suggest new routes for fabrication of complex soft material structures in Janus drops and other confinement geometries.
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Affiliation(s)
- Wei-Shao Wei
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA.
- Laboratory for Research on the Structure of Matter (LRSM), University of Pennsylvania, Philadelphia, PA, USA
| | - Joonwoo Jeong
- Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea.
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA.
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA.
- Laboratory for Research on the Structure of Matter (LRSM), University of Pennsylvania, Philadelphia, PA, USA
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4
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Stenull O, de la Cotte A, Ettinger S, Collings PJ, Yodh AG, Lubensky TC. Theory of director fluctuations about a hedgehog defect in a nematic drop. Phys Rev E 2022; 105:044703. [PMID: 35590662 DOI: 10.1103/physreve.105.044703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 03/16/2022] [Indexed: 06/15/2023]
Abstract
We present calculations of eigenmode energies and wave functions of both azimuthal and polar distortions of the nematic director relative to a radial hedgehog trapped in a spherical drop with a smaller concentric spherical droplet at its core. All surfaces interior to the drop have perpendicular (homeotropic) boundary conditions. We also calculate director correlation functions and their relaxation times. Of particular interest is a critical mode whose energy, with fixed Frank constants, vanishes as the ratio μ=R_{2}/R_{1} increases toward a critical value μ_{c}, where R_{2} is the radius of the drop and R_{1} that of the inner droplet, and then becomes negative for μ>μ_{c}. Our calculations form a basis for interpreting experimental measurements of director fluctuations relative to a radial hedgehog state in a spherical drop. We compare results with those obtained by previous investigations, which use a calculational approach different from ours, and with our experimental observations.
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Affiliation(s)
- Olaf Stenull
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Alexis de la Cotte
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Sophie Ettinger
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - T C Lubensky
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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5
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de la Cotte A, Stenull O, Ettinger S, Collings PJ, Lubensky TC, Yodh AG. Giant director fluctuations in liquid crystal drops. Phys Rev E 2022; 105:044702. [PMID: 35590637 DOI: 10.1103/physreve.105.044702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 02/02/2022] [Indexed: 06/15/2023]
Abstract
We report the discovery and elucidation of giant spatiotemporal orientational fluctuations in nematic liquid crystal drops with radial orientation of the nematic anisotropy axis producing a central "hedgehog" defect. We study the spatial and temporal properties of the fluctuations experimentally using polarized optical microscopy, and theoretically, by calculating the eigenspectrum of the Frank elastic free energy of a nematic drop of radius R_{2}, containing a spherical central core of radius R_{1} and constrained by perpendicular boundary conditions on all surfaces. We find that the hedgehog defect with radial orientation has a complex excitation spectrum with a single critical mode whose energy vanishes at a critical value μ_{c} of the ratio μ=R_{2}/R_{1}. When μ<μ_{c}, the mode has positive energy, indicating that the radial hedgehog state is stable; when μ>μ_{c}, it has negative energy indicating that the radial state is unstable to the formation of a lower-energy state. This mode gives rise to the large-amplitude director fluctuations we observe near the core, for μ near μ_{c}. A collapse of the experimental data corroborates model predictions for μ<μ_{c} and provides an estimate of the defect core size.
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Affiliation(s)
- Alexis de la Cotte
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Olaf Stenull
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Sophie Ettinger
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Tom C Lubensky
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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6
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Ettinger S, Dietrich CF, Mishra CK, Miksch C, Beller DA, Collings PJ, Yodh AG. Rods in a lyotropic chromonic liquid crystal: emergence of chirality, symmetry-breaking alignment, and caged angular diffusion. Soft Matter 2022; 18:487-495. [PMID: 34851348 DOI: 10.1039/d1sm01209f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In lyotropic chromonic liquid crystals (LCLCs), twist distortion of the nematic director costs much less energy than splay or bend distortion. This feature leads to novel mirror-symmetry breaking director configurations when the LCLCs are confined by interfaces or contain suspended particles. Spherical colloids in an aligned LCLC nematic phase, for example, induce chiral director perturbations ("twisted tails"). The asymmetry of rod-like particles in an aligned LCLC offer a richer set of possibilities due to their aspect ratio (α) and mean orientation angle (〈θ〉) between their long axis and the uniform far-field director. Here we report on the director configuration, equilibrium orientation, and angular diffusion of rod-like particles with planar anchoring suspended in an aligned LCLC. Video microscopy reveals, counterintuitively, that two-thirds of the rods have an angled equilibrium orientation (〈θ〉 ≠ 0) that decreases with increasing α, while only one-third of the rods are aligned (〈θ〉 = 0). Polarized optical video-microscopy and Landau-de Gennes numerical modeling demonstrate that the angled and aligned rods are accompanied by distinct chiral director configurations. Angled rods have a longitudinal mirror plane (LMP) parallel to their long axis and approximately parallel to the substrate walls. Aligned rods have a transverse and longitudinal mirror plane (TLMP), where the transverse mirror plane is perpendicular to the rod's long axis. Effectively, the small twist elastic constant of LCLCs promotes chiral director configurations that modify the natural tendency of rods to orient along the far-field director. Additional diffusion experiments confirm that rods are angularly confined with strength that depends on α.
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Affiliation(s)
- Sophie Ettinger
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA.
| | - Clarissa F Dietrich
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Chandan K Mishra
- Discipline of Physics, Indian Institute of Technology (IIT) Gandhinagar, Palaj, Gandhinagar, Gujarat 382355, India
| | - Cornelia Miksch
- Max Planck Institute of Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
| | - Daniel A Beller
- Department of Physics, University of California, Merced, CA, 95343, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA.
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA, 19081, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA.
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7
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Dietrich CF, Rudquist P, Collings PJ, Giesselmann F. Interplay between Confinement, Twist Elasticity, and Intrinsic Chirality in Micellar Lyotropic Nematic Liquid Crystals. Langmuir 2021; 37:2749-2758. [PMID: 33577330 DOI: 10.1021/acs.langmuir.0c03500] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Recent studies have shown that lyotropic nematic liquid crystals (LLCs) are exceptional in their viscoelastic behavior. In particular, LLCs display a remarkable softness to twist deformations, which may lead to chiral director configurations under achiral confinement despite the absence of intrinsic chirality. The twisted escaped radial (TER) and the twisted polar (TP) are the two representative reflection symmetry breaking director configurations in the case of cylindrical confinement with homeotropic anchoring. We demonstrate how such reflection symmetry breaking of micellar LLCs under cylindrical confinement is affected by intrinsic chirality, introduced by the addition of a chiral dopant. Similarities and differences between the effects of intrinsic chirality on the defect-free TER configuration, and on the TP configuration incorporating two half-unit twist disclination lines, are discussed. In the TP case, topological constraints facilitate stable heterochiral systems even in the presence of a small amount of chiral dopant, with unusual regions of rapidly reversing handedness between homochiral domains. At moderate dopant concentrations, the TP structure becomes homochiral. At high dopant concentrations, for which the induced cholesteric pitch is much smaller than the diameter of the capillary, the cholesteric fingerprint structure develops.
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Affiliation(s)
- Clarissa F Dietrich
- Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
| | - Per Rudquist
- Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, United States
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Frank Giesselmann
- Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
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8
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Abstract
The two main classes of liquid crystals are thermotropic (containing no solvent) and lyotropic (containing solvent). Both of these classes possess the nematic phase, the most simple of liquid crystal phases with only uniaxial orientational order. For both of these classes, if the constituent molecules are chiral or if a chiral dopant is added, the preferred direction of orientation rotates in helical fashion in what is called the chiral nematic phase. Recent research has shown that because the ordering entities of the two classes are quite different (molecules versus molecular assemblies), important differences in the properties of the nematic phase can result. While thermotropic chiral nematics have been extensively examined, less is known about lyotropic chiral nematics, especially for the most ideal case, a chiral-racemic system. Furthermore, none of the lyotropic chiral-racemic studies has included lyotropic chromonic liquid crystals, which are solutions of dyes, drugs, and nucleic acids. Inverse pitch measurements are reported for a chiral-racemic system of a chromonic liquid crystal across the entire chiral fraction range and over a 30 °C temperature interval. The inverse pitch depends linearly on chiral fraction and decreases with increasing temperature, indicating that achiral and chiral molecules participate in the assembly structure similarly. The helical twisting power is significantly larger than for other chiral lyotropic liquid crystals due to the very high scission energy of the investigated system.
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Affiliation(s)
- Jordan K Ando
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA.
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA. and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
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9
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Abstract
One of the most simple cases in which chirality at the microscopic level produces a chiral macroscopic structure is the chiral nematic liquid crystal phase. In such a phase, the preferred direction of molecular orientation rotates in helical fashion, with the pitch of the helix in different systems ranging from around 100 nm to as large as can be measured (∼10 mm). For almost all thermotropic and lyotropic liquid crystals, the ordered entities are formed from strong bonds, so the pitch varies in accordance with how the interactions between these largely immutable entities are affected by changing conditions. A unique exception are lyotropic chromonic liquid crystals (LCLCs) that spontaneously form weakly bound assemblies in solution, the size of which depends strongly on experimental parameters. While the temperature dependence of the pitch has been measured for chiral LCLCs formed by short strands of DNA (DNA-LCLCs), such is not the case for chiral LCLCs formed by small molecules. Polarized optical microscopy experiments on small molecule chiral LCLCs reveal the changing assembly size through a temperature dependence of the pitch not typical for many other systems, including the most recent measurements on DNA-LCLCs. In fact, the pitch measurements in small molecule chiral LCLCs strongly increase in value as the temperature is increased and the assemblies shrink in size. Theoretical considerations provide some help in understanding this phenomena, but leave much to be explained.
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Affiliation(s)
- Timothy Ogolla
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA. and Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA, USA
| | - Robert S Paley
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA, USA
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA. and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
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10
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Martinez A, Collings PJ, Yodh AG. Brownian Dynamics of Particles "Dressed" by Chiral Director Configurations in Lyotropic Chromonic Liquid Crystals. Phys Rev Lett 2018; 121:177801. [PMID: 30411945 DOI: 10.1103/physrevlett.121.177801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Indexed: 06/08/2023]
Abstract
We study Brownian dynamics of colloidal spheres, with planar anchoring conditions, suspended in the nematic phase of the lyotropic chromonic liquid crystal disodium chromoglycate (DSCG). Unlike typical liquid crystals, the unusually small twist elastic modulus of DSCG permits two energetically distinct helical distortions (twisted tails) of the nematic director to "dress" the suspended spheres. Video microscopy is used to characterize the helical distortions versus particle size and to measure particle mean-square displacements. Diffusion coefficients parallel and perpendicular to the far-field director, and their anisotropy ratio, are different for the two twisted tail configurations. Moreover, the crossover from subdiffusive to diffusive behavior is anomalously slow for motion perpendicular to the director (>100 s). Simple arguments using Miesowicz viscosities and ideas about twist relaxation are suggested to understand the mean-square displacement observations.
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Affiliation(s)
- Angel Martinez
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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11
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Davidson ZS, Huang Y, Gross A, Martinez A, Still T, Zhou C, Collings PJ, Kamien RD, Yodh AG. Deposition and drying dynamics of liquid crystal droplets. Nat Commun 2017; 8:15642. [PMID: 28555621 PMCID: PMC5460001 DOI: 10.1038/ncomms15642] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 04/13/2017] [Indexed: 11/09/2022] Open
Abstract
Drop drying and deposition phenomena reveal a rich interplay of fundamental science and engineering, give rise to fascinating everyday effects (coffee rings), and influence technologies ranging from printing to genotyping. Here we investigate evaporation dynamics, morphology, and deposition patterns of drying lyotropic chromonic liquid crystal droplets. These drops differ from typical evaporating colloidal drops primarily due to their concentration-dependent isotropic, nematic, and columnar phases. Phase separation occurs during evaporation, and in the process creates surface tension gradients and significant density and viscosity variation within the droplet. As a result, the drying multiphase drops exhibit different convective currents, drop morphologies, and deposition patterns (coffee-rings). When particle-laden drops evaporate, coffee ring patterns form which can affect particle deposition. Here Davidson et al. show that unlike previously investigated drops, the flows in drying drops of liquid crystals are driven by an increase in surface tension due to liquid crystal concentration.
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Affiliation(s)
- Zoey S Davidson
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Yongyang Huang
- Department of Electrical &Computer Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA
| | - Adam Gross
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Angel Martinez
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Tim Still
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Chao Zhou
- Department of Electrical &Computer Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA.,Department of Electrical &Computer Engineering, Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania 18015, USA
| | - Peter J Collings
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.,Department of Physics &Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Randall D Kamien
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - A G Yodh
- Department of Physics &Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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12
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Collings PJ. Report on the 26th international liquid crystal conference. Liquid Crystals Today 2017. [DOI: 10.1080/1358314x.2017.1279441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Peter J. Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA, USA
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13
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Gratale MD, Still T, Matyas C, Davidson ZS, Lobel S, Collings PJ, Yodh AG. Tunable depletion potentials driven by shape variation of surfactant micelles. Phys Rev E 2016; 93:050601. [PMID: 27300818 DOI: 10.1103/physreve.93.050601] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Indexed: 06/06/2023]
Abstract
Depletion interaction potentials between micron-sized colloidal particles are induced by nanometer-scale surfactant micelles composed of hexaethylene glycol monododecyl ether (C_{12}E_{6}), and they are measured by video microscopy. The strength and range of the depletion interaction is revealed to arise from variations in shape anisotropy of the surfactant micelles. This shape anisotropy increases with increasing sample temperature. By fitting the colloidal interaction potentials to theoretical models, we extract micelle length and shape anisotropy as a function of temperature. This work introduces shape anisotropy tuning as a means to control interparticle interactions in colloidal suspensions, and it shows how the interparticle depletion potentials of micron-scale objects can be employed to probe the shape and size of surrounding macromolecules at the nanoscale.
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Affiliation(s)
- Matthew D Gratale
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Tim Still
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Caitlin Matyas
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- The Arts Academy at Benjamin Rush, Philadelphia, Pennsylvania 19154, USA
| | - Zoey S Davidson
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Samuel Lobel
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - A G Yodh
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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14
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Jeong J, Gross A, Wei WS, Tu F, Lee D, Collings PJ, Yodh AG. Liquid crystal Janus emulsion droplets: preparation, tumbling, and swimming. Soft Matter 2015; 11:6747-6754. [PMID: 26171829 DOI: 10.1039/c5sm01053e] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This study introduces liquid crystal (LC) Janus droplets. We describe a process for the preparation of these droplets, which consist of nematic LC and polymer compartments. The process employs solvent-induced phase separation in emulsion droplets generated by microfluidics. The droplet morphology was systematically investigated and demonstrated to be sensitive to the surfactant concentration in the background phase, the compartment volume ratio, and the possible coalescence of multiple Janus droplets. Interestingly, the combination of a polymer and an anisotropic LC introduces new functionalities into Janus droplets, and these properties lead to unusual dynamical behaviors. The different densities and solubilities of the two compartments produce gravity-induced alignment, tumbling, and directional self-propelled motion of Janus droplets. LC Janus droplets with remarkable optical properties and dynamical behaviors thus offer new avenues for applications of Janus colloids and active soft matter.
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Affiliation(s)
- Joonwoo Jeong
- School of Natural Science, Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea.
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15
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Davidson ZS, Kang L, Jeong J, Still T, Collings PJ, Lubensky TC, Yodh AG. Chiral structures and defects of lyotropic chromonic liquid crystals induced by saddle-splay elasticity. Phys Rev E Stat Nonlin Soft Matter Phys 2015; 91:050501. [PMID: 26066106 DOI: 10.1103/physreve.91.050501] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Indexed: 06/04/2023]
Abstract
An experimental and theoretical study of lyotropic chromonic liquid crystals (LCLCs) confined in cylinders with degenerate planar boundary conditions elucidates LCLC director configurations. When the Frank saddle-splay modulus is more than twice the twist modulus, the ground state adopts an inhomogeneous escaped-twisted configuration. Analysis of the configuration yields a large saddle-splay modulus, which violates Ericksen inequalities but not thermodynamic stability. Lastly, we observe point defects between opposite-handed domains, and we explain a preference for point defects over domain walls.
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Affiliation(s)
- Zoey S Davidson
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Louis Kang
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Joonwoo Jeong
- School of Natural Science, Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea
| | - Tim Still
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Peter J Collings
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Tom C Lubensky
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - A G Yodh
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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16
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Zimmermann N, Jünnemann-Held G, Collings PJ, Kitzerow HS. Self-organized assemblies of colloidal particles obtained from an aligned chromonic liquid crystal dispersion. Soft Matter 2015; 11:1547-1553. [PMID: 25589441 DOI: 10.1039/c4sm02579b] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The behavior of mono-disperse colloidal particles in a chromonic liquid crystal was investigated. Poly(methyl methacrylate) spherical particles with three different functionalizations, with and without surface charges, were utilized in the nematic and columnar phases of disodium cromoglycate solutions. The nematic phase was completely aligned parallel to the glass substrates by a simple rubbing technique, and the columnar phase showed regions of similar alignment. The behavior of the colloidal particles in the chromonic liquid crystal depended critically on the functionality, with bromine functionalized particles not dispersing at all, and cationic trimethylammonium and epoxy functionalized particles dispersing well in the isotropic phase of the liquid crystal. At the transition to the nematic and especially the columnar phase, the colloidal particles were expelled into the remaining isotropic phase. Since the columnar phase grew in parallel ribbons, the colloidal particles ended up in chain-like assemblies. Such behavior opens the possibility of producing patterned assemblies of colloidal particles by taking advantage of the self-organized structure of chromonic liquid crystals.
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Affiliation(s)
- Natalie Zimmermann
- Department of Chemistry, University of Paderborn, 33098 Paderborn, Germany.
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17
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Collings PJ. Call for applications to host the 27th International Liquid Crystal Conference (Summer, 2018). Liquid Crystals Today 2015. [DOI: 10.1080/1358314x.2014.973264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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18
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Abstract
IR-806 is a near-infrared cyanine dye that undergoes a two-step assembly process in aqueous solutions. The final assemblies orientationally order into a liquid crystal at a very low concentration (∼0.6 wt % at room temperature). While the first step of the assembly process is continuous as the dye concentration or temperature is varied (isodesmic), the second step is more abrupt (cooperative). Because the absorption spectrum of IR-806 changes dramatically during the assembly process, careful equilibrium and kinetic absorption experiments are utilized to examine the details of the cooperative second step. These experiments involve changes in both concentration and temperature, allowing a close thermodynamic analysis of the assembly process. Both equilibrium and kinetic investigations reveal that the assembly process is highly cooperative and can be described by multiple models (for example, nucleation and growth) in the highly cooperative limit. The enthalpy associated with the growth process and the activation energy of the rate-limiting step during disassembly are determined. These findings have significant implications for the structure of the assemblies that form the liquid crystal phase in IR-806.
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Affiliation(s)
- Benjamin R Mercado
- Department of Physics & Astronomy, Swarthmore College , Swarthmore, Pennsylvania 19081, United States
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19
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Agra-Kooijman DM, Singh G, Lorenz A, Collings PJ, Kitzerow HS, Kumar S. Columnar molecular aggregation in the aqueous solutions of disodium cromoglycate. Phys Rev E Stat Nonlin Soft Matter Phys 2014; 89:062504. [PMID: 25019802 DOI: 10.1103/physreve.89.062504] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Indexed: 05/11/2023]
Abstract
Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 Å between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from ∼35 to 42 Å in the orientationally ordered nematic (N) phase and from 27 to 32 Å in the columnar or middle (M) phase having long range lateral positional order. The assemblies' length depends on concentration and consists of ∼23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values ∼7.19 ± 0.14 k_{B}T (15 wt %), 2.73 ± 0.4 k_{B}T (20 wt %), and 3.05 ± 0.2 k_{B}T (25 wt %). Solutions of all concentrations undergo a spinodal decomposition at temperatures above ∼40 °C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases.
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Affiliation(s)
| | - Gautam Singh
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Alexander Lorenz
- Department of Chemistry, Berlin Institute of Technology, Strasse des 17. Juni 124, 10623 Berlin, Germany
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Heinz-S Kitzerow
- Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany
| | - Satyendra Kumar
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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20
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Subramanian D, Klauda JB, Collings PJ, Anisimov MA. Mesoscale Phenomena in Ternary Solutions of Tertiary Butyl Alcohol, Water, and Propylene Oxide. J Phys Chem B 2014; 118:5994-6006. [DOI: 10.1021/jp4125183] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | | | - Peter J. Collings
- Department
of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, United States
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21
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Lohr MA, Cavallaro M, Beller DA, Stebe KJ, Kamien RD, Collings PJ, Yodh AG. Elasticity-dependent self-assembly of micro-templated chromonic liquid crystal films. Soft Matter 2014; 10:3477-3484. [PMID: 24651876 DOI: 10.1039/c3sm53170h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We explore micropatterned director structures of aqueous lyotropic chromonic liquid crystal (LCLC) films created on square-lattice cylindrical-micropost substrates. The structures are manipulated by modulating the LCLC mesophases and their elastic properties via concentration through drying. Nematic LCLC films exhibit preferred bistable alignment along the diagonals of the micropost lattice. Columnar LCLC films, dried from nematics, form two distinct director and defect configurations: a diagonally aligned director pattern with local squares of defects, and an off-diagonal configuration with zig-zag defects. The formation of these states appears to be tied to the relative splay and bend free energy costs of the initial nematic films. The observed nematic and columnar configurations are understood numerically using a Landau-de Gennes free energy model. Among other attributes, the work provide first examples of quasi-2D micropatterning of LC films in the columnar phase and lyotropic LC films in general, and it demonstrates alignment and configuration switching of typically difficult-to-align LCLC films via bulk elastic properties.
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Affiliation(s)
- Matthew A Lohr
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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22
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Jeong J, Han G, Johnson ATC, Collings PJ, Lubensky TC, Yodh AG. Homeotropic alignment of lyotropic chromonic liquid crystals using noncovalent interactions. Langmuir 2014; 30:2914-20. [PMID: 24559290 DOI: 10.1021/la404893t] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications.
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Affiliation(s)
- Joonwoo Jeong
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
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23
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McGinn CK, Laderman LI, Zimmermann N, Kitzerow HS, Collings PJ. Planar anchoring strength and pitch measurements in achiral and chiral chromonic liquid crystals using 90-degree twist cells. Phys Rev E Stat Nonlin Soft Matter Phys 2013; 88:062513. [PMID: 24483474 DOI: 10.1103/physreve.88.062513] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2013] [Indexed: 06/03/2023]
Abstract
Chromonic liquid crystals are formed by molecules that spontaneously assemble into anisotropic structures in water. The ordering unit is therefore a molecular assembly instead of a molecule as in thermotropic liquid crystals. Although it has been known for a long time that certain dyes, drugs, and nucleic acids form chromonic liquid crystals, only recently has enough knowledge been gained on how to control their alignment so that studies of their fundamental liquid crystal properties can be performed. In this article, a simple method for producing planar alignment of the nematic phase in chromonic liquid crystals is described, and this in turn is used to create twisted nematic structures of both achiral and chiral chromonic liquid crystals. The optics of 90-degree twist cells allows the anchoring strength to be measured in achiral systems, which for this alignment technique is quite weak, about 3×10(-7) J/m(2) for both disodium cromoglycate and Sunset Yellow FCF. The addition of a chiral amino acid to the system causes the chiral nematic phase to form, and similar optical measurements in 90-degree twist cells produce a measurement of the intrinsic pitch of the chiral nematic phase. From these measurements, the helical twisting power for L-alanine is found to be (1.1±0.4)×10(-2) μm(-1) wt%(-1) for 15 wt% disodium cromoglycate.
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Affiliation(s)
- Christine K McGinn
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Laura I Laderman
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
| | - Natalie Zimmermann
- Department of Chemistry, University of Paderborn, 33098 Paderborn, F. R. Germany
| | - Heinz-S Kitzerow
- Department of Chemistry, University of Paderborn, 33098 Paderborn, F. R. Germany
| | - Peter J Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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24
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Mills EA, Regan MH, Stanic V, Collings PJ. Large Assembly Formation via a Two-Step Process in a Chromonic Liquid Crystal. J Phys Chem B 2012; 116:13506-15. [DOI: 10.1021/jp306135w] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Elizabeth A. Mills
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, United States
| | - Margaret H. Regan
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, United States
| | - Vesna Stanic
- Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York 11973,
United States
| | - Peter J. Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, United States
- Department
of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania
19014, United States
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25
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Collings PJ, Dierking I. Society News. Liquid Crystals Today 2010. [DOI: 10.1080/1358314x.2010.10586368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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26
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McKitterick CB, Erb-Satullo NL, LaRacuente ND, Dickinson AJ, Collings PJ. Aggregation Properties of the Chromonic Liquid Crystal Benzopurpurin 4B. J Phys Chem B 2010; 114:1888-96. [DOI: 10.1021/jp910136p] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Christopher B. McKitterick
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19014
| | - Nathaniel L. Erb-Satullo
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19014
| | - Nicholas D. LaRacuente
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19014
| | - Alexandra J. Dickinson
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19014
| | - Peter J. Collings
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19014
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27
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Tomasik MR, Collings PJ. Aggregation Behavior and Chromonic Liquid Crystal Phase of a Dye Derived from Naphthalenecarboxylic Acid. J Phys Chem B 2008; 112:9883-9. [DOI: 10.1021/jp803648g] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Michelle R. Tomasik
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Peter J. Collings
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
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28
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Horowitz VR, Janowitz LA, Modic AL, Heiney PA, Collings PJ. Aggregation behavior and chromonic liquid crystal properties of an anionic monoazo dye. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:041710. [PMID: 16383405 DOI: 10.1103/physreve.72.041710] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2005] [Indexed: 05/05/2023]
Abstract
X-ray scattering and various optical techniques are utilized to study the aggregation process and chromonic liquid crystal phase of the anionic monoazo dye Sunset Yellow FCF. The x-ray results demonstrate that aggregation involves pi-pi stacking of the molecules into columns, with the columns undergoing a phase transition to an orientationally ordered chromonic liquid crystal phase at high dye concentration. Optical absorption measurements on dilute solutions reveal that the aggregation takes place at all concentrations, with the average aggregation number increasing with concentration. A simple theory based on the law of mass action and an isodesmic aggregation process is in excellent agreement with the experimental data and yields a value for the "bond" energy between molecules in an aggregate. Measurements of the birefringence and order parameter are also performed as a function of temperature in the chromonic liquid crystal phase. The agreement between these results and a more complicated theory of aggregation is quite reasonable. Overall, these results both confirm that the aggregation process for some dyes is isodesmic and provide a second example of a well-characterized chromonic system.
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Affiliation(s)
- Viva R Horowitz
- Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA
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29
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Abstract
Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.
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Affiliation(s)
- A M Alsayed
- Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104-6396, USA
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30
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Chanishvili A, Chilaya G, Petriashvili G, Collings PJ. Trans-cis isomerization and the blue phases. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 71:051705. [PMID: 16089549 DOI: 10.1103/physreve.71.051705] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Indexed: 05/03/2023]
Abstract
A new class of photoactive chiral liquid crystals based on a photoactive nematic host material and a photoinactive chiral dopant was utilized to investigate the behavior of the blues phases when trans-cis isomerization is induced. While the general behavior follows what has been observed in the cholesteric phase, the sensitivity of the blue phases to external parameters causes different behavior when these systems are exposed to UV radiation. The results for four different mixtures are reported and include (1) modulation of the blue phase selective reflection wavelength with low levels of UV and visible light, (2) conversion of one blue phase to another upon exposure to UV light, and (3) induction of blue phases due to UV irradiation when no blue phases are stable beforehand. It is also noted that the supercooled blue phase behaves differently from the other blue phases. All of these results can be understood qualitatively from the ratio of non-nematogenic cis isomers to nematogenic trans isomers and chiral molecules.
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Affiliation(s)
- Andro Chanishvili
- Institute of Cybernetics of the Georgian Academy of Sciences, Euli Str. 5, 0186 Tbilisi, Georgia
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31
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Krich JJ, Romanowsky MB, Collings PJ. Correlation length and chirality of the fluctuations in the isotropic phase of nematic and cholesteric liquid crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 71:051712. [PMID: 16089556 DOI: 10.1103/physreve.71.051712] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Indexed: 05/03/2023]
Abstract
Light-scattering measurements of the correlation length in the isotropic phase of a nematic liquid crystal reveal a temperature dependence following Landau-de Gennes theory for the isotropic phase with a bare correlation length smaller than has been measured in other liquid crystals. Similar measurements in a cholesteric liquid crystal demonstrate that the correlation length in the isotropic phase is larger than typically found in nematics and that the chirality of the fluctuations in the isotropic phase is slightly higher than the chirality of the cholesteric phase. Landau-de Gennes theory of the cholesteric phase describes the chirality in the cholesteric phase well but predicts that the chirality in the isotropic phase is temperature independent, which is not consistent with the data. There is a discontinuity in the chirality at the cholesteric-isotropic transition of about 15%, which is less than the predictions of Landau-de Gennes theory but more than the typical specific volume discontinuity at transitions to the isotropic phase. Except for a mismatch in the discontinuities at the transition, the chirality data resemble the temperature behavior of variables just below a critical point, in spite of the fact that this system is far from a critical point.
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Affiliation(s)
- Jacob J Krich
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
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32
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Collings PJ, Ratna BR, Shashidhar R. Order parameter measurements of dichroic dyes dissolved in smectic liquid crystals that tilt without layer contraction. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 67:021705. [PMID: 12636698 DOI: 10.1103/physreve.67.021705] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2002] [Indexed: 05/24/2023]
Abstract
Measurements of the orientational order parameter of dissolved dichroic dyes are reported for two smectic-A liquid crystals that tilt in the presence of an in-plane electric field without any decrease in the layer spacing. The dye order parameter is determined by measuring the anisotropic absorption of linearly polarized light. Different dyes are used and measurements are also performed on a smectic liquid crystal that tilts with the expected layer contraction to check how closely the measurements reflect the order parameter of the liquid crystal. The variation of the dye order parameter with electric field is in accordance with the recently proposed model of azimuthal disorder of the tilt angle direction, but the surprising finding is that the local dye orientational order parameter is significantly lower than for the smectic liquid crystal that tilts with the expected layer contraction. This suggests that another mechanism might be contributing significantly to the smectic order, one possibility of which is the tendency for different parts of these siloxane-containing molecules to segregate within each layer. Another possible explanation is that the azimuthal disorder is due to a modulated phase with a high enough density of defects to decrease the value of the local order parameter.
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Affiliation(s)
- Peter J Collings
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Code 6900, 4555 Overlook Avenue, SW, Washington, D.C. 20375, USA
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33
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Pasternack RF, Bustamante C, Collings PJ, Giannetto A, Gibbs EJ. Porphyrin assemblies on DNA as studied by a resonance light-scattering technique. J Am Chem Soc 2002. [DOI: 10.1021/ja00066a006] [Citation(s) in RCA: 738] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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34
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Lacoste D, Collings PJ, Lubensky TC. Effective index of refraction, optical rotation, and circular dichroism in isotropic chiral liquid crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:031717. [PMID: 11909091 DOI: 10.1103/physreve.65.031717] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2001] [Indexed: 05/23/2023]
Abstract
This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependence of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric P is much shorter than the wavelength of the light lambda, an approximation that has been made in previous studies of this problem. The theoretical predictions are supported by comparing them with experimental spectra of the optical activity in the BP III phase.
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Affiliation(s)
- D Lacoste
- Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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35
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Collings PJ, Kamien RD. Book Reviews. Liquid Crystals Today 2002. [DOI: 10.1080/1358314x.2002.10586287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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36
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Selinger JV, Collings PJ, Shashidhar R. Field-dependent tilt and birefringence of electroclinic liquid crystals: theory and experiment. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 64:061705. [PMID: 11736200 DOI: 10.1103/physreve.64.061705] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2001] [Indexed: 11/07/2022]
Abstract
An unresolved issue in the theory of liquid crystals is the molecular basis of the electroclinic effect in the smectic-A phase. Recent x-ray scattering experiments suggest that, in a class of siloxane-containing liquid crystals, an electric field changes a state of disordered molecular tilt in random directions into a state of ordered tilt in one direction. To investigate this issue, we measure the optical tilt and birefringence of these liquid crystals as functions of field and temperature, and we develop a theory for the distribution of molecular orientations under a field. A comparison of theory and experiment confirms that these materials have a disordered distribution of molecular tilt directions that is aligned by an electric field, giving a large electroclinic effect. It also shows that the effective dipole moment, a key parameter in the theory, scales as a power law near the smectic-A--smectic-C transition.
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Affiliation(s)
- J V Selinger
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Code 6900, 4555 Overlook Avenue SW, Washington, D.C. 20375, USA
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37
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Abstract
The kinetics of J-aggregate formation has been studied for two chromophores, tetrakis-4-sulfonatophenylporphine in an acid medium and pseudoisocyanine on a polyvinylsulfonate template. The assembly processes differ both in their sensitivity to initiation protocols and in the reaction profiles they produce. The porphyrin's assembly kinetics, for example, displays an induction period unlike that of the cyanine dye. Two kinetic models are presented. For the porphyrin, an autocatalytic pathway in which the formation of an aggregation nucleus is rate-determining appears to be applicable; for the pseudoisocyanine dye, an equation derived for diffusion-limited aggregation of a fractal object satisfactorily fits the data. These models are shown to be useful for the analysis of kinetic data obtained for several biologically important aggregation processes.
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Affiliation(s)
- R F Pasternack
- Department of Chemistry, Swarthmore College, Swarthmore Pennsylvania 19081, USA
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38
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Huff BP, Krich JJ, Collings PJ. Helix inversion in the chiral nematic and isotropic phases of a liquid crystal. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 61:5372-5378. [PMID: 11031587 DOI: 10.1103/physreve.61.5372] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/1999] [Revised: 12/10/1999] [Indexed: 05/23/2023]
Abstract
Measurements of the chirality (2 pi/pitch) in the chiral nematic phase and of a structural constant proportional to the chirality in the isotropic liquid for a system in which a helix inversion line crosses the chiral nematic to isotropic phase transition line are reported. While the chirality shows a strong temperature dependence in the chiral nematic phase, it loses all temperature dependence in the isotropic phase. In addition, the chirality in the isotropic phase is proportional to the chirality in the chiral nematic phase at the phase transition, and may in fact be continuous across the transition. While molecular field and phenomenological theories can explain the strong temperature dependence in the chiral nematic phase, including the helix inversion, these theories predict a strong discontinuity in the chirality at the phase transition that is not supported by experiment. So while a theory that includes short range molecular correlations is called for to understand the behavior of the chirality across the phase transition, theoretical attempts to explain the chirality of a phase from a microscopic level must account for the strong role played by long range orientational order.
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Affiliation(s)
- BP Huff
- Department of Physics and Astronomy, Swarthmore College, Pennsylvania 19081, USA
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Collings PJ, Gibbs EJ, Starr TE, Vafek O, Yee C, Pomerance LA, Pasternack RF. Resonance Light Scattering and Its Application in Determining the Size, Shape, and Aggregation Number for Supramolecular Assemblies of Chromophores. J Phys Chem B 1999. [DOI: 10.1021/jp991610s] [Citation(s) in RCA: 219] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Peter J. Collings
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Esther J. Gibbs
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Tammy E. Starr
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Oskar Vafek
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Cyril Yee
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Laura A. Pomerance
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Robert F. Pasternack
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081; Department of Chemistry, Goucher College, Towson, Maryland 21204; and Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081
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Affiliation(s)
- Colin Nuckolls
- Contribution from The Department of Chemistry, Columbia University, New York, New York 10027, and The Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Thomas J. Katz
- Contribution from The Department of Chemistry, Columbia University, New York, New York 10027, and The Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Gail Katz
- Contribution from The Department of Chemistry, Columbia University, New York, New York 10027, and The Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Peter J. Collings
- Contribution from The Department of Chemistry, Columbia University, New York, New York 10027, and The Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
| | - Louis Castellanos
- Contribution from The Department of Chemistry, Columbia University, New York, New York 10027, and The Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081
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Pasternack RF, Gibbs EJ, Collings PJ, dePaula JC, Turzo LC, Terracina A. A Nonconventional Approach to Supramolecular Formation Dynamics. The Kinetics of Assembly of DNA-Bound Porphyrins. J Am Chem Soc 1998. [DOI: 10.1021/ja980186q] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert F. Pasternack
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
| | - Esther J. Gibbs
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
| | - Peter J. Collings
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
| | - Julio C. dePaula
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
| | - L. Christine Turzo
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
| | - Antonio Terracina
- Contribution from the Department of Chemistry and Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, Department of Chemistry, Goucher College, Towson, Maryland 21204, Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041, and Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell' Università di Messina, Messina, Italy
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Collings PJ. The Contributions of Horst Stegemeyer to Blue Phase Research. Liquid Crystals Today 1997. [DOI: 10.1080/13583149708047664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Kao MH, Jester KA, Yodh AG, Collings PJ. Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals. Phys Rev Lett 1996; 77:2233-2236. [PMID: 10061892 DOI: 10.1103/physrevlett.77.2233] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Kutnjak Z, Garland CW, Schatz CG, Collings PJ, Booth CJ, Goodby JW. Critical point for the blue-phase-III-isotropic phase transition in chiral liquid crystals. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1996; 53:4955-4963. [PMID: 9964824 DOI: 10.1103/physreve.53.4955] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Abstract
Light scattering experiments are usually performed at wavelengths away from absorption bands, but for species that aggregate, enhancements in light scattering of several orders of magnitude can be observed at wavelengths characteristic of these species. Resonance light scattering is shown to be a sensitive and selective method for studying electronically coupled chromophore arrays. The approach is illustrated with several examples drawn from porphyrin and chlorin chemistry. The physical principles underlying resonance light scattering are discussed, and the advantages and limitations of the technique are reviewed.
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Affiliation(s)
- R F Pasternack
- Department of Chemistry, Swarthmore College, PA 19081, USA
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Kutnjak Z, Garland CW, Passmore JL, Collings PJ. Supercritical conversion of the third blue phase to the isotropic phase in a highly chiral liquid crystal. Phys Rev Lett 1995; 74:4859-4862. [PMID: 10058617 DOI: 10.1103/physrevlett.74.4859] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Bowling MB, Collings PJ, Booth CJ, Goodby JW. Phase diagrams for the blue phases of highly chiral liquid crystals. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1993; 48:4113-4115. [PMID: 9961074 DOI: 10.1103/physreve.48.4113] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Rosenzweig JD, Collings PJ. Optical activity in the smectic-A phase of a highly chiral liquid crystal. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1993; 47:1876-1880. [PMID: 9960209 DOI: 10.1103/physreve.47.1876] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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