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Revignas D, Ferrarini A. Microscopic modelling of nematic elastic constants beyond Straley theory. SOFT MATTER 2022; 18:648-661. [PMID: 34935844 DOI: 10.1039/d1sm01502h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Recent findings on various classes of nematics, whose microscopic structure differs from the prototypical rod-like shape, evidence unusual elastic properties, which challenge existing theories. Here we develop a theoretical and numerical methodology for the calculation of Frank elastic constants, accounting for the coupling between the molecular shape and each specific deformation mode. This is done in the framework of Onsager-Straley's second-virial theory, using a non-local form of the orientational distribution function. The comparison between two benchmark systems, a straight and a bent rod, allows us to illustrate the distinct features of this approach, which include additional order parameters induced by the deformation and, related to this, an ideal contribution to the deformation free energy. Then, using a simple system that can be seen as a minimalist model of liquid crystal trimers, we discuss the impact of different molecular conformations on elastic constants.
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Affiliation(s)
- Davide Revignas
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy.
| | - Alberta Ferrarini
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy.
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Velez JX, Zheng Z, Beller DA, Serra F. Emergence and stabilization of transient twisted defect structures in confined achiral liquid crystals at a phase transition. SOFT MATTER 2021; 17:3848-3854. [PMID: 33885449 DOI: 10.1039/d0sm02040k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Spontaneous emergence of chirality is a pervasive theme in soft matter. We report a transient twist forming in achiral nematic liquid crystals confined to a capillary tube with square cross section. At the smectic-nematic phase transition, intertwined disclination line pairs are observed with both helical and kinked lozenge-like contours, configurations that we promote through capillary cross-section geometry and stabilize using fluorescent amphiphilic molecules. The observed texture is similar to that found in "exotic" materials such as chromonics, but it is here observed in common thermotropic nematics upon heating from the smectic into the nematic phase. Numerical modeling further reveals that the disclinations may possess winding characters that are intermediate between wedge and twist, and that vary along the defect contours. In our experiments, we utilize a phase transition to generate otherwise elusive defect structures in common liquid crystal materials.
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Affiliation(s)
- Jose X Velez
- Johns Hopkins University, Dept. Physics and Astronomy, Baltimore, USA.
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Bagnani M, Azzari P, De Michele C, Arcari M, Mezzenga R. Elastic constants of biological filamentous colloids: estimation and implications on nematic and cholesteric tactoid morphologies. SOFT MATTER 2021; 17:2158-2169. [PMID: 33443281 DOI: 10.1039/d0sm01886d] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Biological liquid crystals, originating from the self-assembly of biological filamentous colloids, such as cellulose and amyloid fibrils, show a complex lyotropic behaviour that is extremely difficult to predict and characterize. Here we analyse the liquid crystalline phases of amyloid fibrils, and sulfated and carboxylated cellulose nanocrystals and measure their Frank-Oseen elastic constants K1, K2 and K3 by four different approaches. The first two approaches are based on the benchmark of the predictions of: (i) a scaling form and (ii) a variational form of the Frank-Oseen energy functional with the experimental critical volumes at order-order liquid crystalline transitions of the tactoids. The third and the fourth methods imply: (iii) the direct scaling equations of elastic constants and (iv) a molecular theory predicting the elastic constants from the experimentally accessible contour length distributions of the filamentous colloids. These three biological systems exhibit diverse liquid crystalline behaviour, governed by the distinct elastic constants characterizing each colloid. Differences and similarities among the three systems are highlighted and interpreted based on the present analysis, providing a general framework to study dispersed liquid crystalline systems.
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Affiliation(s)
- Massimo Bagnani
- ETH Zurich, Department of Health Sciences and Technology, Schmelzbergstrasse 9, LFO E23 Zurich 8092, Switzerland
| | - Paride Azzari
- ETH Zurich, Department of Health Sciences and Technology, Schmelzbergstrasse 9, LFO E23 Zurich 8092, Switzerland
| | - Cristiano De Michele
- "Sapienza" Universita' di Roma, Dipartimento di Fisica, P.le A. Moro 2, 00185 Roma, Italy
| | - Mario Arcari
- ETH Zurich, Department of Health Sciences and Technology, Schmelzbergstrasse 9, LFO E23 Zurich 8092, Switzerland
| | - Raffaele Mezzenga
- ETH Zurich, Department of Health Sciences and Technology, Schmelzbergstrasse 9, LFO E23 Zurich 8092, Switzerland and ETH Zurich, Department of Materials, Wolfgang-Pauli-Strasse 10, Zurich 8093, Switzerland.
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Revignas D, Ferrarini A. Interplay of Particle Morphology and Director Distortions in Nematic Fluids. PHYSICAL REVIEW LETTERS 2020; 125:267802. [PMID: 33449752 DOI: 10.1103/physrevlett.125.267802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 10/16/2020] [Accepted: 10/26/2020] [Indexed: 06/12/2023]
Abstract
The existing microscopic theories for elasticity of nematics are challenged by recent findings on systems, whether bent molecules or semiflexible polymers, which do not comply with the model of rigid rodlike particles. Here, we propose an extension of Onsager-Straley second-virial theory, based on a model for the orientational distribution function that, through explicit account of the director profile along a particle, changes in the presence of deformations. The elastic constants reveal specific effects of particle morphology, which are not captured by the existing theories. This paves the way to microscopic modeling of the elastic properties of semiflexible liquid crystal polymers, which is a longstanding issue.
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Affiliation(s)
- Davide Revignas
- Università di Padova, Dipartimento di Scienze Chimiche, via Marzolo 1, 35131 Padova, Italy
| | - Alberta Ferrarini
- Università di Padova, Dipartimento di Scienze Chimiche, via Marzolo 1, 35131 Padova, Italy
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Abstract
We introduce and shortly summarize a variety of more recent aspects of lyotropic liquid crystals (LLCs), which have drawn the attention of the liquid crystal and soft matter community and have recently led to an increasing number of groups studying this fascinating class of materials, alongside their normal activities in thermotopic LCs. The diversity of topics ranges from amphiphilic to inorganic liquid crystals, clays and biological liquid crystals, such as viruses, cellulose or DNA, to strongly anisotropic materials such as nanotubes, nanowires or graphene oxide dispersed in isotropic solvents. We conclude our admittedly somewhat subjective overview with materials exhibiting some fascinating properties, such as chromonics, ferroelectric lyotropics and active liquid crystals and living lyotropics, before we point out some possible and emerging applications of a class of materials that has long been standing in the shadow of the well-known applications of thermotropic liquid crystals, namely displays and electro-optic devices.
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Wensink HH. Polymeric Nematics of Associating Rods: Phase Behavior, Chiral Propagation, and Elasticity. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b01421] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Henricus H. Wensink
- Laboratoire de Physique des Solides—UMR 8502, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
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Bagnani M, Nyström G, De Michele C, Mezzenga R. Amyloid Fibrils Length Controls Shape and Structure of Nematic and Cholesteric Tactoids. ACS NANO 2019; 13:591-600. [PMID: 30543398 DOI: 10.1021/acsnano.8b07557] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Amyloid fibrils offer the possibility of controlling their contour length, aspect ratio, and length distribution, without affecting other structural parameters. Here we show that a fine control in the contour length distribution of β-lactoglobulin amyloid fibrils, achieved by mechanical shear stresses of different levels, translates into the organization of tactoids of different shapes and morphologies. While longer fibrils lead to highly elongated nematic tactoids in an isotropic continuous matrix, only sufficiently shortened amyloid fibrils lead to cholesteric droplets. The progressive decrease in amyloid fibrils length leads to a linear decrease of the anchoring strength and homogeneous tactoid → bipolar tactoid → cholesteric droplet transitions. Upon fibrils length increase, we first find experimentally and predict theoretically a decrease of the cholesteric pitch, before full disappearance of the cholesteric phase. The latter is understood to arise from the decrease of the energy barrier separating cholesteric and nematic phases over thermal energy for progressively longer, semiflexible fibrils.
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Affiliation(s)
- Massimo Bagnani
- Department of Health Science and Technology , ETH Zurich , Schmelzbergstrasse 9, LFO E23 Zurich 8092 , Switzerland
| | - Gustav Nyström
- Department of Health Science and Technology , ETH Zurich , Schmelzbergstrasse 9, LFO E23 Zurich 8092 , Switzerland
| | - Cristiano De Michele
- Dipartimento di Fisica , "Sapienza" Università di Roma , P.le A. Moro 2 , 00185 Roma , Italy
| | - Raffaele Mezzenga
- Department of Health Science and Technology , ETH Zurich , Schmelzbergstrasse 9, LFO E23 Zurich 8092 , Switzerland
- Department of Materials , ETH Zurich , Wolfgang-Pauli-Strasse 10 , Zurich 8093 , Switzerland
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Nguyen KT, De Michele C. Nematic liquid crystals of bifunctional patchy spheres. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2018; 41:141. [PMID: 30552517 DOI: 10.1140/epje/i2018-11750-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 11/09/2018] [Indexed: 06/09/2023]
Abstract
Anisotropic interactions can bring about the formation, through self-assembly, of semi-flexible chains, which in turn can give rise to nematic phases for suitable temperatures and concentrations. A minimalist model constituted of hard cylinders decorated with attractive sites has been already extensively studied numerically. Simulation data shows that a theoretical approach recently proposed is able to properly capture the physical properties of these self-assembly-driven liquid crystals. Here, we investigated a simpler model constituted of bifunctional Kern-Frenkel hard spheres which does not possess steric anisotropy but which can undergo a istropic-nematic transition as a result of their self-assembly into semi-flexible chains. For this model we compare an accurate numerical estimate of isotropic-nematic phase boundaries with theoretical predictions. The theoretical treatment, originally proposed for cylinder-like particles, has been greatly simplified and its predictions are in good agreement with numerical results. Finally, we also assess a crucial, and not obvious, hypothesis used in the theory, i.e. the ability of the Onsager trial function to properly model particle orientation in the presence of aggregation, that has not been properly checked yet.
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Affiliation(s)
- Khanh Thuy Nguyen
- Dipartimento di Fisica, "Sapienza" Università di Roma, P.le A. Moro 2, 00185, Roma, Italy
| | - Cristiano De Michele
- Dipartimento di Fisica, "Sapienza" Università di Roma, P.le A. Moro 2, 00185, Roma, Italy.
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Han L, Zhu S, Ma H, Liu P, Shen H, Yang L, Huang W, Li Y. Assessing the Sequence Specificity in Thermal and Polarized Optical Order of Multiple Sequence-Determined Liquid Crystal Polymers. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01585] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Li Han
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Siqi Zhu
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Hongwei Ma
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Pibo Liu
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Heyu Shen
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Lincan Yang
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Wei Huang
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Yang Li
- State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, Liaoning key Laboratory of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
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