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Klopp C, Trittel T, Stannarius R. Coarsening of Quasi Two-Dimensional Emulsions Formed by Islands in Free-Standing Smectic Films. Chemphyschem 2024; 25:e202400166. [PMID: 38529677 DOI: 10.1002/cphc.202400166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 03/24/2024] [Accepted: 03/25/2024] [Indexed: 03/27/2024]
Abstract
We study the coarsening behavior of assemblies of islands on smectic A freely suspended films in ISS microgravity experiments. The islands can be regarded as liquid inclusions in a two-dimensional fluid in analogy to liquid droplets of the discontinuous phase of an emulsion. The coarsening is effectuated by two processes, predominantly by island coalescence, but to some extend also by Ostwald ripening, whereby large islands grow at the expense of surrounding smaller ones. A peculiarity of this system is that the continuous and the discontinuous phases consist of the same material. We determine the dynamics, analyze the self-similar aging of the island size distribution and discuss characteristic exponents of the mean island growth.
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Affiliation(s)
- Christoph Klopp
- Otto von Guericke University Magdeburg, Institute of Physics, Universtiätsplatz 2, D-39106, Magdeburg, Germany
- Otto von Guericke University Magdeburg, MARS, D-39106, Magdeburg, Germany
| | - Torsten Trittel
- Brandenburg University of Applied Sciences, Department of Engineering, Magdeburger Straße 50, D-14770, Brandenburg an der Havel, Germany
- Otto von Guericke University Magdeburg, MARS, D-39106, Magdeburg, Germany
| | - Ralf Stannarius
- Otto von Guericke University Magdeburg, Institute of Physics, Universtiätsplatz 2, D-39106, Magdeburg, Germany
- Brandenburg University of Applied Sciences, Department of Engineering, Magdeburger Straße 50, D-14770, Brandenburg an der Havel, Germany
- Otto von Guericke University Magdeburg, MARS, D-39106, Magdeburg, Germany
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2
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Kralj N, Ravnik M, Kos Ž. Defect Line Coarsening and Refinement in Active Nematics. PHYSICAL REVIEW LETTERS 2023; 130:128101. [PMID: 37027875 DOI: 10.1103/physrevlett.130.128101] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Revised: 02/09/2023] [Accepted: 02/15/2023] [Indexed: 06/19/2023]
Abstract
Active matter is naturally out of equilibrium which results in the emergence of diverse dynamic steady states, including the omnipresent chaotic state known as the active turbulence. However, much less is known how active systems dynamically depart out of these configurations, such as get excited or damped to a different dynamic steady state. In this Letter, we demonstrate the coarsening and refinement dynamics of topological defect lines in three-dimensional active nematic turbulence. Specifically, using theory and numerical modeling, we are able to predict the evolution of the active defect density away from the steady state due to time-dependent activity or viscoelastic material properties, establishing a single length scale phenomenological description of defect line coarsening and refinement in a three-dimensional active nematic. The approach is first applied to growth dynamics of a single active defect loop, and then to a full three-dimensional active defect network. More generally, this Letter provides insight into the general coarsening phenomena between dynamical regimes in 3D active matter, with a possible analogy in other physical systems.
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Affiliation(s)
- Nika Kralj
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
| | - Miha Ravnik
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
- Condensed Matter Physics Department, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Žiga Kos
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
- Condensed Matter Physics Department, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
- International Institute for Sustainability with Knotted Chiral Meta Matter, Hiroshima University, Higashihiroshima 739-8511, Japan
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3
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Hölbl A, Mesarec L, Polanšek J, Iglič A, Kralj S. Stable Assemblies of Topological Defects in Nematic Orientational Order. ACS OMEGA 2023; 8:169-179. [PMID: 36643572 PMCID: PMC9835183 DOI: 10.1021/acsomega.2c07174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 12/07/2022] [Indexed: 06/17/2023]
Abstract
We considered general mechanisms enabling the stabilization of localized assemblies of topological defects (TDs). There is growing evidence that physical fields represent fundamental natural entities, and therefore these features are of interest to all branches of physics. In general, cores of TDs are energetically costly, and consequently, assemblies of TDs are unfavorable. Owing to the richness of universalities in the physics of TDs, it is of interest to identify systems where they are easily experimentally accessible, enabling detailed and well-controlled analysis of their universal behavior, and cross-fertilizing knowledge in different areas of physics. In this respect, thermotropic nematic liquid crystals (NLCs) represent an ideal experiment testbed for such studies. In addition, TDs in NLCs could be exploited in several applications. We present examples that emphasize the importance of curvature imposed on the phase component of the relevant order parameter field. In NLCs, it is represented by the nematic tensor order parameter. Using a simple Landau-type approach, we show how the coupling between chirality and saddle splay elasticity, which can be expressed as a Gaussian curvature contribution, can stabilize Meron TDs. The latter have numerous analogs in other branches of physics. TDs in 2D curved manifolds reveal that the Gaussian curvature dominantly impacts the assembling and stabilization of TDs. Furthermore, a strong enough curvature that serves as an attractor for TDs is a respective field that could be imposed in a fast enough phase transition. Assemblies of created TDs created in such a disordered environment could be stabilized by appropriate impurities.
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Affiliation(s)
- Arbresha Hölbl
- Faculty of Natural
Sciences and Mathematics, University of
Maribor, Koroška
160, 2000 Maribor, Slovenia
| | - Luka Mesarec
- Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, 1000 Ljubljana, Slovenia
| | - Juš Polanšek
- Faculty of Natural
Sciences and Mathematics, University of
Maribor, Koroška
160, 2000 Maribor, Slovenia
| | - Aleš Iglič
- Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, 1000 Ljubljana, Slovenia
| | - Samo Kralj
- Faculty of Natural
Sciences and Mathematics, University of
Maribor, Koroška
160, 2000 Maribor, Slovenia
- Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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4
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Polanšek J, Holbl A, Starzonek S, Drozd-Rzoska A, Rzoska SJ, Kralj S. History-dependent phase transition character. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2022; 45:70. [PMID: 35997865 PMCID: PMC9399213 DOI: 10.1140/epje/s10189-022-00221-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 07/26/2022] [Indexed: 06/15/2023]
Abstract
We consider history-dependent behavior in domain-type configurations in orientational order that are formed in configurations reached via continuous symmetry-breaking phase transitions. In equilibrium, these systems exhibit in absence of impurities a spatially homogeneous order. We focus on cases where domains are formed via (i) Kibble-Zurek mechanism in fast enough quenches or by (ii) Kibble mechanism in strongly supercooled phases. In both cases, domains could be arrested due to pinned topological defects that are formed at domain walls. In systems exhibiting polar or quadrupolar order, point and line defects (disclinations) dominate, respectively. In particular, the disclinations could form complex entangled structures and are more efficient in stabilizing domains. Domain patterns formed by fast quenches could be arrested by impurities imposing a strong enough random-field type disorder, as suggested by the Imry-Ma theorem. On the other hand, domains formed in supercooled systems could be also formed if large enough energy barriers arresting domains are established due to large enough systems' stiffness. The resulting effective interactions in established domain-type patterns could be described by random matrices. The resulting eigenvectors reveal expected structural excitations formed in such structures. The most important role is commonly played by the random matrix largest eigenvector. Qualitatively different behavior is expected if this eigenvector exhibits a localized or extended character. In the former case, one expects a gradual, non-critical-type transition into a glass-type structure. However, in the latter case, a critical-like phase behavior could be observed.
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Affiliation(s)
- Juš Polanšek
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000, Maribor, Slovenia
| | - Arbresha Holbl
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000, Maribor, Slovenia
| | - Szymon Starzonek
- Institute of High Pressure Physics Polish Academy of Sciences, ul. Sokołowska 29/37, 01-142, Warsaw, Poland.
| | - Aleksandra Drozd-Rzoska
- Institute of High Pressure Physics Polish Academy of Sciences, ul. Sokołowska 29/37, 01-142, Warsaw, Poland
| | - Sylwester J Rzoska
- Institute of High Pressure Physics Polish Academy of Sciences, ul. Sokołowska 29/37, 01-142, Warsaw, Poland
| | - Samo Kralj
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000, Maribor, Slovenia
- Condensed Matter Physics Department, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
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5
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Birdi N, Underwood TL, Wilding NB, Puri S, Banerjee V. Equilibrium phases and domain growth kinetics of calamitic liquid crystals. Phys Rev E 2022; 105:024706. [PMID: 35291087 DOI: 10.1103/physreve.105.024706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 01/29/2022] [Indexed: 06/14/2023]
Abstract
The anisotropic shape of calamitic liquid crystal (LC) particles results in distinct values of energy when the nematogens are placed side by side or end to end. This anisotropy in energy which is governed by a parameter κ^{'} has deep consequences on equilibrium and nonequilibrium properties. Using the Gay-Berne (GB) model, which exhibits the nematic (Nm) as well as the low-temperature smectic (Sm) order, we undertake large-scale Monte Carlo and molecular dynamics simulations to probe the effect of κ^{'} on the equilibrium phase diagram and the nonequilibrium domain growth following a quench in the temperature T or coarsening. There are two transitions in the GB model: (i) isotropic to Nm at T_{c}^{1} and (ii) Nm to Sm at T_{c}^{2}<T_{c}^{1}. κ^{'} decreases T_{c}^{1} significantly but has relatively little effect on T_{c}^{2}. Domain growth in the Nm phase exhibits the well-known Lifshitz-Allen-Cahn (LAC) law, L(t)∼t^{1/2} and the evolution is via annihilation of string defects. The system exhibits dynamical scaling that is also robust with respect to κ^{'}. We find that the Sm phase at the quench temperatures T (T>T_{c}^{1}→T<T_{c}^{2}) that we consider has SmB order with a hexatic arrangement of the LC molecules in the layers (SmB-H phase). Coarsening in this phase exhibits a striking two-timescale scenario: First, the LC molecules align and develop orientational order (or nematicity), followed by the emergence of the characteristic layering (or smecticity) along with the hexatic bond-orientational-order within the layers. Consequently, the growth follows the LAC law L(t)∼t^{1/2} at early times and then shows a sharp crossover to a slower growth regime at later times. Our observations strongly suggest that L(t)∼t^{1/4} in this regime. Interestingly, the correlation function shows dynamical scaling in both the regimes and the scaling function is universal. The dynamics is also robust with respect to changes in κ^{'}, but the smecticity is more pronounced at larger values. Further, the early-time dynamics is governed by string defects, while the late-time evolution is dictated by interfacial defects. We believe this scenario is generic to the Sm phase even with other kinds of local order within the Sm layers.
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Affiliation(s)
- Nishant Birdi
- School of Interdisciplinary Research, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
| | - Tom L Underwood
- Department of Chemistry, University of Bath, Bath BA2 7AY, United Kingdom
| | - Nigel B Wilding
- H. H. Wills Physics Laboratory, University of Bristol, Royal Fort, Bristol BS8 1TL, United Kingdom
| | - Sanjay Puri
- School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Varsha Banerjee
- School of Interdisciplinary Research, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
- Department of Physics, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
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Roller J, Laganapan A, Meijer JM, Fuchs M, Zumbusch A. Observation of liquid glass in suspensions of ellipsoidal colloids. Proc Natl Acad Sci U S A 2021; 118:e2018072118. [PMID: 33397813 PMCID: PMC7826331 DOI: 10.1073/pnas.2018072118] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Despite the omnipresence of colloidal suspensions, little is known about the influence of colloid shape on phase transformations, especially in nonequilibrium. To date, real-space imaging results at high concentrations have been limited to systems composed of spherical colloids. In most natural and technical systems, however, particles are nonspherical, and their structural dynamics are determined by translational and rotational degrees of freedom. Using confocal microscopy of fluorescently labeled core-shell particles, we reveal that suspensions of ellipsoidal colloids form an unexpected state of matter, a liquid glass in which rotations are frozen while translations remain fluid. Image analysis unveils hitherto unknown nematic precursors as characteristic structural elements of this state. The mutual obstruction of these ramified clusters prevents liquid crystalline order. Our results give insight into the interplay between local structures and phase transformations. This helps to guide applications such as self-assembly of colloidal superstructures and also gives evidence of the importance of shape on the glass transition in general.
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Affiliation(s)
- Jörg Roller
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany
| | - Aleena Laganapan
- Department of Physics, University of Konstanz, 78464 Konstanz, Germany
| | - Janne-Mieke Meijer
- Department of Physics, University of Konstanz, 78464 Konstanz, Germany
- Institute of Physics, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Matthias Fuchs
- Department of Physics, University of Konstanz, 78464 Konstanz, Germany;
| | - Andreas Zumbusch
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany;
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7
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Riahinasab ST, Keshavarz A, Melton CN, Elbaradei A, Warren GI, Selinger RLB, Stokes BJ, Hirst LS. Nanoparticle-based hollow microstructures formed by two-stage nematic nucleation and phase separation. Nat Commun 2019; 10:894. [PMID: 30796213 PMCID: PMC6385213 DOI: 10.1038/s41467-019-08702-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 01/23/2019] [Indexed: 12/27/2022] Open
Abstract
Rapid bulk assembly of nanoparticles into microstructures is challenging, but highly desirable for applications in controlled release, catalysis, and sensing. We report a method to form hollow microstructures via a two-stage nematic nucleation process, generating size-tunable closed-cell foams, spherical shells, and tubular networks composed of closely packed nanoparticles. Mesogen-modified nanoparticles are dispersed in liquid crystal above the nematic-isotropic transition temperature (TNI). On cooling through TNI, nanoparticles first segregate into shrinking isotropic domains where they locally depress the transition temperature. On further cooling, nematic domains nucleate inside the nanoparticle-rich isotropic domains, driving formation of hollow nanoparticle assemblies. Structural differentiation is controlled by nanoparticle density and cooling rate. Cahn-Hilliard simulations of phase separation in liquid crystal demonstrate qualitatively that partitioning of nanoparticles into isolated domains is strongly affected by cooling rate, supporting experimental observations that cooling rate controls aggregate size. Microscopy suggests the number and size of internal voids is controlled by second-stage nucleation.
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Affiliation(s)
- Sheida T Riahinasab
- Department of Physics, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | - Amir Keshavarz
- Department of Chemistry & Chemical Biology, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | - Charles N Melton
- Department of Physics, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | - Ahmed Elbaradei
- Department of Physics, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | - Gabrielle I Warren
- Department of Chemistry & Chemical Biology, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | | | - Benjamin J Stokes
- Department of Chemistry & Chemical Biology, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA
| | - Linda S Hirst
- Department of Physics, School of Natural Sciences, University of California, Merced, Merced, CA, 95343, USA.
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8
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Jánossy I, Tóth-Katona T, Kósa T, Sukhomlinova L. Super-twist generation and instabilities in photosensitive liquid crystal cells. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2017.12.071] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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9
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Atzin N, Guzmán O, Gutiérrez O, Hirst LS, Ghosh S. Free-energy model for nanoparticle self-assembly by liquid crystal sorting. Phys Rev E 2018; 97:062704. [PMID: 30011549 DOI: 10.1103/physreve.97.062704] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Indexed: 06/08/2023]
Abstract
We modeled the experimentally observed self-assembly of nanoparticles (NPs) into shells with diameters up to 10 μm, via segregation from growing nematic domains. Using field-based Monte Carlo simulations, we found the equilibrium configurations of the system by minimizing a free-energy functional that includes effects of excluded-volume interactions among NPs, orientational elasticity, and the isotropic-nematic phase-transition energy. We developed a Gaussian-profile approximation for the liquid crystal (LC) order-parameter field that provides accurate analytical values for the free energy of LC droplets and the associated microshells. This analytical model reveals a first-order transition between equilibrium states with and without microshells, governed mainly by the competition of excluded-volume and phase-transition energies. By contrast, the LC elasticity effects are much smaller and mostly confined to setting the size of the activation barrier for the transition. In conclusion, field-based thermodynamic methods provide a theoretical framework for the self-assembly of NP shells in liquid crystal hosts and suggest that field-based kinetic methods could be useful to simulate and model the time evolution of NP self-assembly coupled to phase separation.
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Affiliation(s)
- Noé Atzin
- Departamento de Física, Universidad Autónoma Metropolitana, Av. San Rafael Atlixco 186, Iztapalapa, Ciudad de México, 09340, México
| | - Orlando Guzmán
- Departamento de Física, Universidad Autónoma Metropolitana, Av. San Rafael Atlixco 186, Iztapalapa, Ciudad de México, 09340, México
| | - Oscar Gutiérrez
- Departamento de Física, Universidad Autónoma Metropolitana, Av. San Rafael Atlixco 186, Iztapalapa, Ciudad de México, 09340, México
| | - Linda S Hirst
- School of Natural Sciences, University of California, Merced, California 95343, USA
| | - Sayantani Ghosh
- School of Natural Sciences, University of California, Merced, California 95343, USA
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10
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Ranjkesh A, Ambrožič M, Kralj S, Sluckin TJ. Computational studies of history dependence in nematic liquid crystals in random environments. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:022504. [PMID: 25353486 DOI: 10.1103/physreve.89.022504] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Indexed: 06/04/2023]
Abstract
Glassy liquid crystalline systems are expected to show significant history-dependent effects. Two model glassy systems are the RAN and SSS (sprinkled silica spin) lattice models. The RAN model is a Lebwohl-Lasher lattice model with locally coupled nematic spins, together with uncorrelated random anisotropy fields at each site, while the SSS model has a finite concentration of impurity spins frozen in random directions. Here Brownian simulation is used to study the effect of different sample histories in the low temperature regime in a three-dimensional (d = 3) model intermediate between SSS and RAN, in which a finite concentration p < p(c) (p(c) the percolation threshold) of frozen spins interacts with neighboring nematic spins with coupling W. Simulations were performed at temperature T ∼ T(NI)/2 (T(NI) the bulk nematic-isotropic transition temperature) for temperature-quenched and field-quenched histories (TQH and FQH, respectively), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Using long-time averages for equilibrated systems, we calculate orientational order parameters and two-point correlation functions. Finite-size scaling was used to determine the range of the orientational ordering, as a function of coupling strength W,p and sample history. Sample history plays a significant role; for given concentration p, as disorder strength W is increased, TQH systems sustain quasi-long-range order (QLRO) and short-range order (SRO). The data are also consistent with a long-range order (LRO) phase at very low disorder strength. By contrast, for FQH and p ≤ 0.1, only LRO and QLRO occur within the range of parameters investigated. The crossover between regimes depends on history, but in general, the FQH phase is more ordered than the AH phase, which is more ordered than the TQH phase. However, at temperatures close to the isotropic-nematic phase transition of pure samples we observe SRO for p = 0.1 even for FQH. We detect also in the QLRO phase a domain-type structural pattern, consistent with ideas introduced by Giamarchi and Doussal [Phys. Rev. B 52, 1242 (1995)] on superconducting flux lattices. In the weak-disorder limit the orientational correlation length obeys the Larkin-Imry-Ma scaling ξ ∼ D(-2/(4-d)).
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Affiliation(s)
- Amid Ranjkesh
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia
| | - Milan Ambrožič
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia
| | - Samo Kralj
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia and Condensed Matter Physics Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Timothy J Sluckin
- Division of Mathematical Sciences, University of Southampton, Southampton, SO17 1BJ, United Kingdom
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11
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Repnik R, Ranjkesh A, Simonka V, Ambrozic M, Bradac Z, Kralj S. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:404201. [PMID: 24025777 DOI: 10.1088/0953-8984/25/40/404201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl-Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic-nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction only for the appropriate history of systems.
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Affiliation(s)
- R Repnik
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000 Maribor, Slovenia
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12
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Mkhonta SK, Elder KR, Huang ZF, Grant M. Microphase separation in comblike liquid-crystalline diblock copolymers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:042602. [PMID: 24229201 DOI: 10.1103/physreve.88.042602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 07/30/2013] [Indexed: 06/02/2023]
Abstract
The interplay between liquid crystallinity and microphase separation in comblike liquid-crystalline diblock copolymers is examined via a Brazovskii-type phenomenological model using both analytical and numerical calculations. For symmetric diblock copolymers we determine a critical electric field that is required to tilt the orientation of the constituent liquid crystals of the polymer side chains in the microphase-separated lamellar state. Such electrically induced reorientation of the liquid-crystal molecules can lead to substantially large changes of lamellar periodicity. Our numerical results show that highly aligned polymer lamellar domains can self-assemble when the liquid-crystal ordering precedes microphase separation, and that weak electric fields can be used to direct the self-assembly process due to the dielectric anisotropy of the liquid-crystal side chains. We also find that phase separation of asymmetric diblock copolymers can coexist with a network of liquid-crystal nematic orientations, with domain morphology depending on the details of copolymer and liquid-crystal coupling.
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Affiliation(s)
- S K Mkhonta
- Department of Physics and Astronomy, Wayne State University, Detroit, Michigan 48201, USA and Department of Physics, University of Swaziland, Private Bag 4, Kwaluseni M201, Swaziland
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