1
|
Pizzirusso A, Berardi R, Muccioli L, Ricci M, Zannoni C. Predicting surface anchoring: molecular organization across a thin film of 5CB liquid crystal on silicon. Chem Sci 2012. [DOI: 10.1039/c1sc00696g] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
|
2
|
Cheung DL, Schmidt M. Quenched-annealed density functional theory for interfacial behavior of hard rods at a hard rod matrix. J Chem Phys 2009; 131:214705. [DOI: 10.1063/1.3267728] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
3
|
Teixeira PIC, Barmes F, Anquetil-Deck C, Cleaver DJ. Simulation and theory of hybrid aligned liquid crystal films. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:011709. [PMID: 19257054 DOI: 10.1103/physreve.79.011709] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Indexed: 05/27/2023]
Abstract
We present a study of the effects of nanoconfinement on a system of hard Gaussian overlap particles interacting with planar substrates through the hard-needle-wall potential, extending earlier work by two of us [D. J. Cleaver and P. I. C. Teixeira, Chem. Phys. Lett. 338, 1 (2001)]. Here, we consider the case of hybrid films, where one of the substrates induces strongly homeotropic anchoring, while the other favors either weakly homeotropic or planar anchoring. These systems are investigated using both Monte Carlo simulation and density-functional theory, the latter implemented at the level of Onsager's second-virial approximation with Parsons-Lee rescaling. The orientational structure is found to change either continuously or discontinuously depending on substrate separation, in agreement with earlier predictions by others. The theory is seen to perform well in spite of its simplicity, predicting the positional and orientational structure seen in simulations even for small particle elongations.
Collapse
Affiliation(s)
- P I C Teixeira
- Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro 1, P-1950-062 Lisbon, Portugal
| | | | | | | |
Collapse
|
4
|
Cheung DL, Allen MP. Effect of substrate geometry on liquid-crystal-mediated nanocylinder-substrate interactions. J Chem Phys 2008; 129:114706. [DOI: 10.1063/1.2977968] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
5
|
de Vos T, Baus M. A density functional study of a twisted nematic cell and its relation to the Frank–Oseen theory. J Chem Phys 2008; 128:194903. [DOI: 10.1063/1.2920198] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
6
|
Cheung DL, Allen MP. Liquid-crystal-mediated force between a cylindrical nanoparticle and substrate. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:041706. [PMID: 17995012 DOI: 10.1103/physreve.76.041706] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Indexed: 05/25/2023]
Abstract
Using classical density functional theory, the structure of a molecular fluid around a cylindrical nanoparticle near a solid substrate is studied. The solvent-mediated force between the nanoparticle and the substrate is calculated in both the nematic and isotropic phases of the solvent. In the nematic phase, the force is short ranged and arises due to interaction between high-density regions near the substrate and nanoparticle. In the isotropic phase, the formation of a nematic bridge between the substrate and nanoparticle gives rise to an attractive force between them. The potential between the nanoparticle and substrate as a function of separation calculated numerically is compared to that calculated from the Derjaguin approximation. In the isotropic phase these are found to be in reasonable agreement at low separations, while the agreement is poorer in the nematic phase.
Collapse
Affiliation(s)
- David L Cheung
- Department of Physics and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom.
| | | |
Collapse
|
7
|
Cheung DL, Allen MP. Structure of a liquid crystalline fluid around a macroparticle: Density functional theory. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 74:021701. [PMID: 17025446 DOI: 10.1103/physreve.74.021701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2006] [Revised: 05/17/2006] [Indexed: 05/12/2023]
Abstract
The structure of a molecular liquid, in both the nematic liquid crystalline and isotropic phases, around a cylindrical macroparticle, is studied using density functional theory. In the nematic phase the structure of the fluid is highly anisotropic with respect to the director, in agreement with results from simulation and phenomenological theories. On going into the isotropic phase the structure becomes rotationally invariant around the macroparticle with an oriented layer at the surface.
Collapse
Affiliation(s)
- David L Cheung
- Department of Physics and Centre for Scientific Computing, University of Warwick, Coventry, CV4 7AL, United Kingdom.
| | | |
Collapse
|
8
|
|
9
|
|
10
|
Cheung DL, Schmid F. Monte Carlo simulations of liquid crystals near rough walls. J Chem Phys 2005; 122:074902. [PMID: 15743265 DOI: 10.1063/1.1844495] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effect of surface roughness on the structure of liquid crystalline fluids near solid substrates is studied by Monte Carlo simulations. The liquid crystal is modeled as a fluid of soft ellipsoidal molecules and the substrate is modeled as a hard wall that excludes the centers of mass of the fluid molecules. Surface roughness is introduced by embedding a number of molecules with random positions and orientations within the wall. It is found that the density and order near the wall are reduced as the wall becomes rougher, i.e., the number of embedded molecules is increased). Anchoring coefficients are determined from fluctuations in the reciprocal space order tensor. It is found that the anchoring strength decreases with increasing surface roughness.
Collapse
Affiliation(s)
- David L Cheung
- Theoretische Physik, Universität Bielefeld, 33615 Bielefeld, Germany
| | | |
Collapse
|
11
|
Cheung DL, Schmid F. A density-functional theory study of the confined soft ellipsoid fluid. J Chem Phys 2004; 120:9185-91. [PMID: 15267855 DOI: 10.1063/1.1703522] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
A system of soft ellipsoid molecules confined between two planar walls is studied using classical density-functional theory. Both the isotropic and nematic phases are considered. The excess free energy is evaluated using two different Ansätze and the intermolecular interaction is incorporated using two different direct correlation functions (DCF's). The first is a numerical DCF obtained from simulations of bulk soft ellipsoid fluids and the second is taken from the Parsons-Lee theory. In both the isotropic and nematic phases the numerical DCF gives density and order parameter profiles in reasonable agreement with simulation. The Parsons-Lee DCF also gives reasonable agreement in the isotropic phase but poor agreement in the nematic phase.
Collapse
Affiliation(s)
- David L Cheung
- Theoretische Physik, Universitat Bielefeld, D-33615 Bielefeld, Germany
| | | |
Collapse
|
12
|
Steuer H, Hess S, Schoen M. Phase behavior of liquid crystals confined by smooth walls. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:031708. [PMID: 15089311 DOI: 10.1103/physreve.69.031708] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2003] [Indexed: 05/24/2023]
Abstract
Monte Carlo simulations for a simple model liquid crystal are presented. The influence of flat walls on the phase behavior is analyzed for two different anchoring mechanisms, one favoring homeotropic alignment and one simulating a twisted nematic cell without external fields, e.g., two walls with different homogeneous planar alignment. The simulations are performed in the constant pressure ensemble. The box volume may change in the directions perpendicular to the wall normal. The isotropic-nematic phase transition in the bulk system is first studied for different isobars. For the weak first order transition we do not observe any hysteresis down to a temperature accuracy of deltaT=0.001. The isotherm T=1 is then studied in the bulk as well as in the confined geometries. The walls stabilize the positional order in the systems due to the formation of layers. The orientational order is weakly stabilized.
Collapse
Affiliation(s)
- Haiko Steuer
- Institut für Theoretische Physik, Technische Universität Berlin, PN7-1, Hardenbergstrasse 36, D-10623 Berlin, Germany.
| | | | | |
Collapse
|
13
|
Guzmán O, Kim EB, Grollau S, Abbott NL, de Pablo JJ. Defect structure around two colloids in a liquid crystal. PHYSICAL REVIEW LETTERS 2003; 91:235507. [PMID: 14683198 DOI: 10.1103/physrevlett.91.235507] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2003] [Indexed: 05/24/2023]
Abstract
This Letter investigates the defect structures that arise between two colloidal spheres immersed in a nematic liquid crystal. Molecular simulations and a dynamic field theory are employed to arrive at molecular-level and mesoscopic descriptions of the systems of interest. At large separations, each sphere is surrounded by a Saturn ring defect. However, at short separations both theory and simulation predict that a third disclination ring appears in between the spheres, in a plane normal to the Saturn rings. This feature gives rise to an effective binding of the particles. The structures predicted by field theory and molecular simulations are consistent with each other.
Collapse
Affiliation(s)
- O Guzmán
- Department of Chemical Engineering, University of Wisconsin, Madison, Wisconsin 53706-1691, USA
| | | | | | | | | |
Collapse
|
14
|
Andrienko D, Tasinkevych M, Patrício P, Allen MP, Telo da Gama MM. Forces between elongated particles in a nematic colloid. ACTA ACUST UNITED AC 2003; 68:051702. [PMID: 14682806 DOI: 10.1103/physreve.68.051702] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2003] [Indexed: 11/07/2022]
Abstract
Using molecular dynamics simulations we study the interactions between elongated colloidal particles (length to breath ratio >>1) in a nematic host. The simulation results are compared to the results of a Landau-de Gennes elastic free energy. We find that depletion forces dominate for the sizes of the colloidal particles studied. The tangential component of the force, however, allows us to resolve the elastic contribution to the total interaction. We find that this contribution differs from the quadrupolar interaction predicted at large separations. The difference is due to the presence of nonlinear effects, namely, the change in the positions and structure of the defects and their annihilation at small separations.
Collapse
Affiliation(s)
- D Andrienko
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | | | | | | | | |
Collapse
|
15
|
Prinsen P, van der Schoot P. Shape and director-field transformation of tactoids. ACTA ACUST UNITED AC 2003; 68:021701. [PMID: 14524987 DOI: 10.1103/physreve.68.021701] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2002] [Revised: 04/02/2003] [Indexed: 11/07/2022]
Abstract
Tactoids are droplets of a nematic phase that under suitable conditions form in dispersions of elongated colloidal particles. We theoretically study the shape and the director-field configuration of such droplets for the case where a planar anchoring of the director field to the interface is favored. A minimum of four regimes can be identified in which the droplets have a different structure. Large droplets tend to be nearly spherical with a director field that is bipolar if the surface tension is strongly anisotropic and homogeneous if this is not so. Small droplets can become very elongated and spindlelike if the surface tension is sufficiently anisotropic. Depending on the anchoring strength, the director field is then either homogeneous or bipolar. We find that the more elongated the tactoid, the more strongly it resists the crossing over from a homogeneous to a bipolar structure. This should have implications for the nucleation rate of the nematic phase. Our calculations qualitatively describe the size dependence of the aspect ratio of tactoids found in recent experiments.
Collapse
Affiliation(s)
- Peter Prinsen
- Polymer Physics Group, Department of Applied Physics and Dutch Polymer Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | | |
Collapse
|