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Sidky H, Whitmer JK. Elastic response and phase behavior in binary liquid crystal mixtures. SOFT MATTER 2016; 12:4489-4498. [PMID: 27093188 DOI: 10.1039/c5sm03107a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Utilizing density-of-states simulations, we perform a full mapping of the phase behavior and elastic responses of binary liquid crystalline mixtures represented by the multicomponent Lebwohl-Lasher model. Our techniques are able to characterize the complete phase diagram, including nematic-nematic phase separation predicted by mean-field theories, but previously not observed in simulations. Mapping this phase diagram permits detailed study of elastic properties across the miscible nematic region. Importantly, we observe for the first time local phase separation and disordering driven by the application of small linear perturbations near the transition temperature and more significantly through nonlinear stresses. These findings are of key importance in systems of blended nematics which contain particulate inclusions, or are otherwise confined.
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Affiliation(s)
- Hythem Sidky
- Department of Chemical and Biomolecular Engineering, University of Notre Dame du Lac, Notre Dame, IN 46556, USA.
| | - Jonathan K Whitmer
- Department of Chemical and Biomolecular Engineering, University of Notre Dame du Lac, Notre Dame, IN 46556, USA.
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2
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Chiccoli C, Pasini P, Teixeira de Souza R, Evangelista LR, Zannoni C. Computer simulations of the ordering in a hybrid cylindrical film of nematic liquid crystals. Phys Rev E 2011; 84:041705. [PMID: 22181155 DOI: 10.1103/physreve.84.041705] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Indexed: 11/07/2022]
Abstract
We present an investigation of the ordering in a nematic liquid-crystal film confined between two cylindrical surfaces with antagonistic (radial and planar) anchoring alignments. A Monte Carlo study of a Lebwohl-Lasher model with suitable boundary conditions has been performed to calculate the ordering and the molecular organization for different film thicknesses. The simulation results are compared with some theoretical predictions obtained with the elastic continuum approach. The agreement between theory and simulation is improved as the thickness decreases.
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Affiliation(s)
- C Chiccoli
- Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
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Caprion D. Discotic molecules in cylindrical nanopores: a Monte Carlo study. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2009; 28:305-313. [PMID: 19190945 DOI: 10.1140/epje/i2008-10412-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Revised: 11/24/2008] [Accepted: 12/19/2008] [Indexed: 05/27/2023]
Abstract
We report Monte Carlo simulations of a model discotic molecule embedded in cylindrical pores. We consider a planar anchoring of the molecules on the surface for two different cylinder radii: R(*) = 5 and R(*) = 10 , in units of the molecular diameter. For both radii, we note that the system is progressively structured in concentric shells when decreasing the temperature. With the small radius, we observe continuous transitions from an isotropic to a nematic phase and then to a crystal one. The radius of the pores is sufficiently small to force the crystal to grow along their main axis. However some orientational discrepancies are observed: some samples present a zigzag configuration. With the big radius, the situation is more complex and it is likely that different scenarios are available. The crystals can be built along the main axis of the cylinders, as for the small radius, but also in any other direction. Thus we observe samples with different orientational domains. In the case of crystals oriented along the nanopore axis, we note that only the first 5 shells close to the wall are sensitive to it.
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Affiliation(s)
- D Caprion
- Royal Meteorological Institute of Belgium, Brussels, Belgium.
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Dickson W, Wurtz GA, Evans PR, Pollard RJ, Zayats AV. Electronically controlled surface plasmon dispersion and optical transmission through metallic hole arrays using liquid crystal. NANO LETTERS 2008; 8:281-286. [PMID: 18085813 DOI: 10.1021/nl072613g] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The enhanced optical properties of metal films periodically perforated with an array of sub-wavelength size holes have recently been widely studied in the field of surface plasmon optics. The ability to design the optical transmission of such nanostructures, which act as plasmonic crystals, by varying their geometrical parameters gives them great flexibility for numerous applications in photonics, opto-electronics, and sensing. Transforming these passive optical elements into devices that may be actively controlled has presented a new challenge. Here, we report on the realization of an electrically controlled nanostructured optical system based on the unique properties of surface plasmon polaritonic crystals in contact with a liquid crystal (LC) layer. We discuss the effect of LC layer modulation on the surface plasmon dispersion, the related optical transmission and the underlying mechanism. The reported effect may be used to achieve active spectral tuneability and switching in a wide range of applications.
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Affiliation(s)
- Wayne Dickson
- Centre for Nanostructured Media, IRCEP, The Queen's University of Belfast, Belfast BT7 1NN, United Kingdom.
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5
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Abstract
Optical simulations of a liquid crystal biosensor device are performed using an integrated optical/textural model based on the equations of nematodynamics and two optical methods: the Berreman optical matrix method [J. Opt. Soc. Am. 62, 502 (1972)] and the discretization of the Maxwell equations based on the finite difference time domain (FDTD) method. Testing the two optical methods with liquid crystal films of different degrees of orientational heterogeneities demonstrates that only the FDTD method is suitable to model this device. Basic substrate-induced texturing process due to protein adsorption gives rise to an orientation correlation function that is nearly linear with the transmitted light intensity, providing a basis to calibrate the device. The sensitivity of transmitted light to film thickness, protein surface coverage, and wavelength is established. A crossover incident light wavelength close to lambda(co) approximately 500 nm is found, such that when lambda>lambda(co) thinner films are more sensitive to the amount of protein surface coverage, while for lambda<lambda(co) the reverse holds. In addition it is found that for all wavelengths the sensitivity increases with the amount of protein coverage. The integrated device model based on FDTD optical simulations in conjunction with the Landau-de Gennes nematodynamics model provides a rational basis for further progress in liquid crystal biosensor devices.
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Affiliation(s)
- Dae Kun Hwang
- Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec H3A 2B2, Canada
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Rodríguez-Ponce I, Romero-Enrique JM, Rull LF. Density functional theory study of the nematic–isotropic transition in an hybrid cell. J Chem Phys 2005; 122:14903. [PMID: 15638696 DOI: 10.1063/1.1829041] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have employed the density functional theory formalism to investigate the nematic-isotropic capillary transitions of a nematogen confined by walls that favor antagonist orientations to the liquid crystal molecules (hybrid cell). We analyze the behavior of the capillary transition as a function of the fluid-substrate interactions and the pore width. In addition to the usual capillary transition between isotropiclike to nematiclike states, we find that this transition can be suppressed when one substrate is wet by the isotropic phase and the other by the nematic phase. Under this condition the system presents interfacelike states which allow us to continuously transform the nematiclike phase to the isotropiclike phase without undergoing a sharp phase transition. Two different mechanisms for the disappearance of the capillary transition are identified. When the director of the nematiclike state is homogeneously planar-anchored with respect to the substrates, the capillary transition ends up in a critical point. This scenario is analogous to the observed in Ising models when confined in slit pores with opposing surface fields which have critical wetting transitions. When the nematiclike state has a linearly distorted director field, the capillary transition continuously transforms in a transition between two nematiclike states.
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Affiliation(s)
- I Rodríguez-Ponce
- Physik Department, Technische Universität München, James-Franck-Strasse, D-85747 Munich, Germany
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Priezjev NV, Skacej G, Pelcovits RA, Zumer S. External and intrinsic anchoring in nematic liquid crystals: a Monte Carlo study. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:041709. [PMID: 14682963 DOI: 10.1103/physreve.68.041709] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2002] [Indexed: 05/24/2023]
Abstract
We present a Monte Carlo study of external surface anchoring in nematic cells with partially disordered solid substrates, as well as of intrinsic anchoring at free nematic interfaces. The simulations are based on the simple hexagonal lattice model with a spatially anisotropic intermolecular potential. We estimate the corresponding extrapolation length b by imposing an elastic deformation in a hybrid cell-like nematic sample. Our estimates for b increase with increasing surface disorder and are essentially temperature independent. Experimental values of b are approached only when both the coupling of nematic molecules with the substrate and the anisotropy of nematic-nematic interactions are weak.
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Affiliation(s)
- N V Priezjev
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA
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Chiccoli C, Pasini P, Skacej G, Zannoni C, Zumer S. Polymer network-induced ordering in a nematogenic liquid: a Monte Carlo study. PHYSICAL REVIEW E 2002; 65:051703. [PMID: 12059573 DOI: 10.1103/physreve.65.051703] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2001] [Indexed: 11/07/2022]
Abstract
In this Monte Carlo study we investigate molecular ordering in a nematogenic liquid with dispersed polymer networks. The polymer network fibers are assumed to have rough surface morphology resulting in a partial randomness in anchoring conditions, while the fiber direction is assumed to be well defined. In particular, we focus on the loss of long-range aligning capability of the network when the degree of disorder in anchoring is increased. This process is monitored by calculating relevant order parameters and the corresponding 2H nuclear magnetic resonance spectra, showing that the aligning ability of the network is lost only for completely disordering anchoring conditions. Moreover, above the nematic-isotropic transition temperature surface-induced paranematic order is detected. In addition, for perfectly smooth fiber surfaces with homeotropic anchoring conditions topological line defects can be observed.
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Affiliation(s)
- C Chiccoli
- INFN, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
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Andrienko D, Allen MP, Skacej G, Zumer S. Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host. PHYSICAL REVIEW E 2002; 65:041702. [PMID: 12005841 DOI: 10.1103/physreve.65.041702] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2001] [Indexed: 11/07/2022]
Abstract
Combining molecular dynamics and Monte Carlo simulation, we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region, we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a particle tilted with respect to the director, and modification of this torque when the particle is close to the cell wall.
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Affiliation(s)
- Denis Andrienko
- H. H. Wills Physics Laboratory, University of Bristol, Royal Fort, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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Andrienko D, Allen MP. Theory and simulation of the nematic zenithal anchoring coefficient. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:021704. [PMID: 11863542 DOI: 10.1103/physreve.65.021704] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2001] [Indexed: 05/23/2023]
Abstract
Combining molecular simulation, Onsager theory, and the elastic description of nematic liquid crystals, we study the dependence of the nematic liquid crystal elastic constants and the zenithal surface anchoring coefficient on the value of the bulk order parameter.
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Affiliation(s)
- Denis Andrienko
- H. H. Wills Physics Laboratory, University of Bristol, Royal Fort, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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24.3: Optical and Mechanical Properties of Stretched PDLC Films for Scattering Polarizers. ACTA ACUST UNITED AC 2002. [DOI: 10.1889/1.1830911] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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