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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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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. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 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] [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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Alsayed AM, Islam MF, Zhang J, Collings PJ, Yodh AG. Premelting at Defects Within Bulk Colloidal Crystals. Science 2005; 309:1207-10. [PMID: 15994377 DOI: 10.1126/science.1112399] [Citation(s) in RCA: 252] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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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Chanishvili A, Chilaya G, Petriashvili G, Collings PJ. Trans-cis isomerization and the blue phases. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 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] [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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Krich JJ, Romanowsky MB, Collings PJ. Correlation length and chirality of the fluctuations in the isotropic phase of nematic and cholesteric liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 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] [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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Collings PJ, Ratna BR, Shashidhar R. Order parameter measurements of dichroic dyes dissolved in smectic liquid crystals that tilt without layer contraction. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Lacoste D, Collings PJ, Lubensky TC. Effective index of refraction, optical rotation, and circular dichroism in isotropic chiral liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Selinger JV, Collings PJ, Shashidhar R. Field-dependent tilt and birefringence of electroclinic liquid crystals: theory and experiment. PHYSICAL REVIEW E 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] [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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Pasternack RF, Fleming C, Herring S, Collings PJ, dePaula J, DeCastro G, Gibbs EJ. Aggregation kinetics of extended porphyrin and cyanine dye assemblies. Biophys J 2000; 79:550-60. [PMID: 10866980 PMCID: PMC1300958 DOI: 10.1016/s0006-3495(00)76316-8] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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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Huff BP, Krich JJ, Collings PJ. Helix inversion in the chiral nematic and isotropic phases of a liquid crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY 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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Nuckolls C, Katz TJ, Katz G, Collings PJ, Castellanos L. Synthesis and Aggregation of a Conjugated Helical Molecule. J Am Chem Soc 1998. [DOI: 10.1021/ja983248l] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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41
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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42
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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] [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. PHYSICAL REVIEW LETTERS 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] [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. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY 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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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45
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Pasternack RF, Collings PJ. Resonance light scattering: a new technique for studying chromophore aggregation. Science 1995; 269:935-9. [PMID: 7638615 DOI: 10.1126/science.7638615] [Citation(s) in RCA: 627] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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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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. PHYSICAL REVIEW LETTERS 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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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47
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Becker JB, Collings PJ. Optical Measurements on the BP III to Isotropic Phase Transition in Highly Chiral Liquid Crystals. ACTA ACUST UNITED AC 1995. [DOI: 10.1080/10587259508041688] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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48
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Bowling MB, Collings PJ, Booth CJ, Goodby JW. Phase diagrams for the blue phases of highly chiral liquid crystals. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY 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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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49
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Rosenzweig JD, Collings PJ. Optical activity in the smectic-A phase of a highly chiral liquid crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY 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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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50
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Wyse JE, Collings PJ. Light scattering in the isotropic phase of highly chiral liquid crystals. PHYSICAL REVIEW. A, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 1992; 45:2449-2454. [PMID: 9907267 DOI: 10.1103/physreva.45.2449] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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