1
|
Lesiuk AI, Ledney MF, Reshetnyak VY. Light-induced Fredericks transition in the nematic liquid crystal cell with plasmonic nanoparticles at a cell bounding substrate. Phys Rev E 2022; 106:024706. [PMID: 36109902 DOI: 10.1103/physreve.106.024706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
The paper presents a theoretical description of the light-induced nematic liquid crystal reorientation in a cell with gold nanoparticles deposited on the surface of one of bounding substrates. It is shown that the surface plasmon resonance in the nanoparticles significantly affects the threshold of the director reorientation. The mathematical model of a surface free-energy density of nematic cell is given, which takes into account the influence of the local electric field on the near-surface nematic layer at the substrate with gold nanoparticles. The threshold intensity of a director orientation instability is calculated and its dependence on the wavelength of incident light and the degree of filling of the surface with gold nanoparticles is analyzed. Comparison of the theoretical calculations with experimental data confirms the full adequacy of the proposed theoretical model.
Collapse
Affiliation(s)
- A I Lesiuk
- National Taras Shevchenko University of Kyiv, Physics Faculty, 64/13, Volodymyrska Street, City of Kyiv 01601, Ukraine
| | - M F Ledney
- National Taras Shevchenko University of Kyiv, Physics Faculty, 64/13, Volodymyrska Street, City of Kyiv 01601, Ukraine
| | - V Yu Reshetnyak
- National Taras Shevchenko University of Kyiv, Physics Faculty, 64/13, Volodymyrska Street, City of Kyiv 01601, Ukraine
| |
Collapse
|
2
|
Basnet B, Rajabi M, Wang H, Kumari P, Thapa K, Paul S, Lavrentovich MO, Lavrentovich OD. Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal. Nat Commun 2022; 13:3932. [PMID: 35798735 PMCID: PMC9262936 DOI: 10.1038/s41467-022-31593-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 06/24/2022] [Indexed: 11/09/2022] Open
Abstract
Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here we demonstrate that polar in-plane surface interactions of a ferroelectric nematic NF produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by \documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${180}^{{{{{{\rm{o}}}}}}}$$\end{document}180o domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by \documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${360}^{{{{{{\rm{o}}}}}}}$$\end{document}360o. The polar contribution to the total surface anchoring strength is on the order of 10%. The domain walls involve splay, bend, and twist of the polarization. The structure suggests that the splay elastic constant is larger than the bend modulus. The \documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$${360}^{{{{{{\rm{o}}}}}}}$$\end{document}360o pairs resemble domain walls in cosmology models with biased vacuums and ferromagnets in an external magnetic field. Surface interactions are usually polar along the normal to the interface and apolar within the interface. Here, the authors find that polar in-plane surface interactions produce domain structures in the bulk of a ferroelectric nematic liquid crystal.
Collapse
Affiliation(s)
- Bijaya Basnet
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.,Materials Science Graduate Program, Kent State University, Kent, OH, 44242, USA
| | - Mojtaba Rajabi
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.,Department of Physics, Kent State University, Kent, OH, 44242, USA
| | - Hao Wang
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA
| | - Priyanka Kumari
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.,Materials Science Graduate Program, Kent State University, Kent, OH, 44242, USA
| | - Kamal Thapa
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.,Department of Physics, Kent State University, Kent, OH, 44242, USA
| | - Sanjoy Paul
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA
| | - Maxim O Lavrentovich
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
| | - Oleg D Lavrentovich
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA. .,Materials Science Graduate Program, Kent State University, Kent, OH, 44242, USA. .,Department of Physics, Kent State University, Kent, OH, 44242, USA.
| |
Collapse
|
3
|
|
4
|
|
5
|
Szilvási T, Bao N, Yu H, Twieg RJ, Mavrikakis M, Abbott NL. The role of anions in adsorbate-induced anchoring transitions of liquid crystals on surfaces with discrete cation binding sites. SOFT MATTER 2018; 14:797-805. [PMID: 29308482 DOI: 10.1039/c7sm01981e] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report a combined theoretical and experimental effort to elucidate systematically for the first time the influence of anions of transition metal salt-decorated surfaces on the orientations of supported films of nematic liquid crystals (LCs) and adsorbate-induced orientational transitions of these LC films. Guided by computational chemistry predictions, we find that nitrate anions weaken the binding of 4'-n-pentyl-4-biphenylcarbonitrile (5CB) to transition metal cations, as compared to perchlorate salts, although binding is still sufficiently strong to induce homeotropic (perpendicular) orientations of 5CB. In addition, we find the orientations of the LC to be correlated across all metal cations investigated by a molecular anchoring energy density that is calculated as the product of the single-site binding energy and metal cation binding site density on the surface. The weaker single-site binding energy caused by nitrate also facilitates competitive binding of adsorbates to the metal cations, leading to more facile orientational transitions induced by adsorbates. Finally, our analysis suggests that nitrate anions recruit water via hydrogen bonding to the metal binding sites, modulating further the relative net binding energies of 5CB and adsorbates to surfaces decorated with metal nitrates. After accounting for the presence of water, we find a universal exponential relationship between the calculated displacement free energies and measured dynamic response of LCs to adsorbates for all metal salts studied, independent of the metal salt anion.
Collapse
Affiliation(s)
- Tibor Szilvási
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706-1607, USA.
| | | | | | | | | | | |
Collapse
|
6
|
Hahm SG, Lee SW, Suh J, Chae B, Kim SB, Lee SJ, Lee KH, Jung JC, Ree M. Rubbed Thin Films of Well-defined Brush Polyimides for Flat-Panel Liquid Crystal Displays: Surface Morphology, Molecular Orientation, and Liquid Crystal Alignability. HIGH PERFORM POLYM 2016. [DOI: 10.1177/0954008306068117] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A series of well-defined brush polyimide (PI) composed of two 4- n-alkyloxyphenyloxy bristles per repeat unit on a semi-rigid poly(4,4′-methylenyldiphenylene pyromellitimide), Cm-PMDA-MDA PIs, were synthesized and their nanoscale thin films prepared by conventional spin-coating of their soluble poly(amic acid) precursor solutions and subsequent drying and thermal imidization in a nitrogen atmosphere. All the PIs were determined to be a positively birefringent polymer. The surface morphology and molecular orientation of each PI in films before and after rubbing were investigated in detail by atomic force microscopy, optical retardation analysis, and linearly polarized infrared spectroscopy. The sequence of the rubbing-induced polymer segmental orientations was further investigated in detail. In addition, the liquid crystal alignment and pretilt ability of the rubbed PI films were examined, and their thermal stability investigated. The present study provides important information on the sequence of the polymer segmental orientations induced by rubbing and additionally the mechanisms of the alignment and pretilt of liquid crystal molecules in contact with the rubbed PI film surface.
Collapse
Affiliation(s)
- Suk Gyu Hahm
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Seung Woo Lee
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Jinsuk Suh
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Boknam Chae
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Seung Bin Kim
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Seong Joon Lee
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Kyung Hoon Lee
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Jin Chul Jung
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| | - Moonhor Ree
- Department of Chemistry, Polymer Research Institute, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea
| |
Collapse
|
7
|
Kim YK, Cukrov G, Xiang J, Shin ST, Lavrentovich OD. Domain walls and anchoring transitions mimicking nematic biaxiality in the oxadiazole bent-core liquid crystal C7. SOFT MATTER 2015; 11:3963-3970. [PMID: 25820380 DOI: 10.1039/c5sm00580a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We investigate the origin of "secondary disclinations" that were recently described as new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. Using an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in a uniaxial nematic phase during the surface anchoring transition, in which surface orientation of the director changes from tangential (parallel to the bounding plates) to tilted. Each domain wall separates two regions with the director tilted in opposite azimuthal directions. At the centre of the wall, the director remains parallel to the bounding plates. The domain walls can be easily removed by applying a moderate electric field. The anchoring transition is explained by the balance of (a) the intrinsic perpendicular surface anchoring produced by the polyimide aligning layer and (b) tangential alignment caused by ionic impurities forming electric double layers. The model is supported by the fact that the temperature of the tangentially tilted anchoring transition decreases as the cell thickness increases and as the concentration of ionic species (added salt) increases. We also demonstrate that the surface alignment is strongly affected by thermal degradation of the samples. This study shows that C7 exhibits only a uniaxial nematic phase and demonstrates yet another mechanism (formation of "secondary disclinations") by which a uniaxial nematic phase can mimic a biaxial nematic behaviour.
Collapse
Affiliation(s)
- Young-Ki Kim
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
| | | | | | | | | |
Collapse
|
8
|
Sai DV, Kumar TA, Haase W, Roy A, Dhara S. Effect of smectic short-range order on the discontinuous anchoring transition in nematic liquid crystals. J Chem Phys 2014; 141:044706. [DOI: 10.1063/1.4890532] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
9
|
Abstract
Colloidal particles in a liquid crystal (LC) behave very differently from their counterparts in isotropic fluids. Elastic nature of the orientational order and surface anchoring of the director cause long-range anisotropic interactions and lead to the phenomenon of levitation. The LC environment enables new mechanisms of particle transport that are reviewed in this work. Among them the motion of particles caused by gradients of the director, and effects in the electric field: backflow powered by director reorientations, dielectrophoresis in LC with varying dielectric permittivity and LC-enabled nonlinear electrophoresis with velocity that depends on the square of the applied electric field and can be directed differently from the field direction.
Collapse
|
10
|
Kim YK, Senyuk B, Shin ST, Kohlmeier A, Mehl GH, Lavrentovich OD. Surface alignment, anchoring transitions, optical properties, and topological defects in the thermotropic nematic phase of organo-siloxane tetrapodes. SOFT MATTER 2014; 10:500-509. [PMID: 24651889 DOI: 10.1039/c3sm52249k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We perform optical, surface anchoring, and textural studies of an organo-siloxane "tetrapode" material in the broad temperature range of the nematic phase. The optical, structural, and topological features are compatible with the uniaxial nematic order rather than with the biaxial nematic order, in the entire nematic temperature range -25 °C < T < 46 °C studied. For homeotropic alignment, the material experiences surface anchoring transition, but the director can be realigned into an optically uniaxial texture by applying a sufficiently strong electric field. The topological features of textures in cylindrical capillaries, in spherical droplets and around colloidal inclusions are consistent with the uniaxial character of the long-range nematic order. In particular, we observe isolated surface point defects - boojums and bulk point defects - hedgehogs that can exist only in the uniaxial nematic liquid crystal.
Collapse
Affiliation(s)
- Young-Ki Kim
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent, OH 44242, USA.
| | | | | | | | | | | |
Collapse
|
11
|
Zola RS, Evangelista LR, Yang YC, Yang DK. Surface induced phase separation and pattern formation at the isotropic interface in chiral nematic liquid crystals. PHYSICAL REVIEW LETTERS 2013; 110:057801. [PMID: 23414046 DOI: 10.1103/physrevlett.110.057801] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2012] [Indexed: 06/01/2023]
Abstract
We study the pattern formation of a chiral nematic liquid crystal under a wetting transition. In the isotropic-liquid crystal transition, a surface-enhanced effect happens and a thin liquid crystal layer forms at the substrates of the cell. In this confined system, chirality, elastic anisotropy, surface anchoring, and wetting strength interplay. A striped pattern is formed due to the chiral nature of the material and the tilted anchoring at the isotropic boundary. As the wetting layer grows from cooling the sample, first the stripes rotate through a process where dislocation defects are formed. As the wetting layer grows further, the periodicity of the stripe structure changes, and finally a splitting of the stripes occurs. Because of the unique properties of this system, new insights about pitch-thickness ratio, interface anchoring, and elastic anisotropy effect are found. Since the anchoring at the isotropic boundary is weak, the critical ratio between the thickness of the wetting layer and the helical pitch is different from that reported in the literature. We also discover that the elastic anisotropy and elastic constant ratios play a critical role in stripe formation. Because of the similarity with biological fibrous composites (twisted plywood), our system may be used as a synthetic version to mimic the naturally occurring one. We carry out a simulation study to explain the experimental results.
Collapse
Affiliation(s)
- R S Zola
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Ohio 44242, USA
| | | | | | | |
Collapse
|
12
|
Carlton RJ, Gupta JK, Swift CL, Abbott NL. Influence of simple electrolytes on the orientational ordering of thermotropic liquid crystals at aqueous interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:31-6. [PMID: 22106820 PMCID: PMC3254853 DOI: 10.1021/la203729t] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We report orientational anchoring transitions at aqueous interfaces of a water-immiscible, thermotropic liquid crystal (LC; nematic phase of 4'-pentyl-4-cyanobiphenyl (5CB)) that are induced by changes in pH and the addition of simple electrolytes (NaCl) to the aqueous phase. Whereas measurements of the zeta potential on the aqueous side of the interface of LC-in-water emulsions prepared with 5CB confirm pH-dependent formation of an electrical double layer extending into the aqueous phase, quantification of the orientational ordering of the LC leads to the proposition that an electrical double layer is also formed on the LC-side of the interface with an internal electric field that drives the LC anchoring transition. Further support for this conclusion is obtained from measurements of the dependence of LC ordering on pH and ionic strength, as well as a simple model based on the Poisson-Boltzmann equation from which we calculate the contribution of an electrical double layer to the orientational anchoring energy of the LC. Overall, the results presented herein provide new fundamental insights into ionic phenomena at LC-aqueous interfaces, and expand the range of solutes known to cause orientational anchoring transitions at LC-aqueous interfaces beyond previously examined amphiphilic adsorbates.
Collapse
Affiliation(s)
- Rebecca J. Carlton
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Jugal K. Gupta
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Candice L. Swift
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Nicholas L. Abbott
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| |
Collapse
|
13
|
Senyuk B, Wonderly H, Mathews M, Li Q, Shiyanovskii SV, Lavrentovich OD. Surface alignment, anchoring transitions, optical properties, and topological defects in the nematic phase of thermotropic bent-core liquid crystal A131. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:041711. [PMID: 21230299 DOI: 10.1103/physreve.82.041711] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2010] [Revised: 09/29/2010] [Indexed: 05/30/2023]
Abstract
We study optical, structural, and surface anchoring properties of thermotropic nematic bent-core material A131. The focus is on the features associated with orientational order as the material has been reported to exhibit not only the usual uniaxial nematic but also the biaxial nematic phase. We demonstrate that A131 experiences a surface anchoring transition from a perpendicular to tilted alignment when the temperature decreases. The features of the tilted state are consistent with surface-induced birefringence associated with smectic layering near the surface and a molecular tilt that changes along the normal to the substrates. The surface-induced birefringence is reduced to zero by a modest electric field that establishes a uniform uniaxial nematic state. Both refractive and absorptive optical properties of A131 are consistent with the uniaxial order. We found no evidence of the "polycrystalline" biaxial behavior in the cells placed in crossed electric and magnetic fields. We observe stable topological point defects (boojums and hedgehogs) and nonsingular "escaped" disclinations pertinent only to the uniaxial order. Finally, freely suspended films of A131 show uniaxial nematic and smectic textures; a decrease in the film thickness expands the temperature range of stability of smectic textures, supporting the idea of surface-induced smectic layering. Our conclusion is that A131 features only a uniaxial nematic phase and that the apparent biaxiality is caused by subtle surface effects rather than by the bulk biaxial phase.
Collapse
Affiliation(s)
- B Senyuk
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
| | | | | | | | | | | |
Collapse
|
14
|
Hahm SG, Jin KS, Park S, Ree M, Kim HS, Kwon SK, Kim YH. The alignment of liquid crystals on the film surfaces of soluble aromatic polyimides bearingt-butylphenyl and trimethylsilylphenyl side groups. Macromol Res 2009. [DOI: 10.1007/bf03218645] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
15
|
Dhara S, Kim JK, Jeong SM, Kogo R, Araoka F, Ishikawa K, Takezoe H. Anchoring transitions of transversely polar liquid-crystal molecules on perfluoropolymer surfaces. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:060701. [PMID: 19658464 DOI: 10.1103/physreve.79.060701] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 05/13/2009] [Indexed: 05/28/2023]
Abstract
We report a strong discontinuous orientational transition (anchoring transition) of liquid-crystal molecules with a large transverse dipole moment. A perfluoropolymer was used as an alignment layer and the transition was observed from planar to homeotropic with decreasing temperature in the nematic phase. Conversely a gradual variation in tilt angle from homeotropic to conical was observed in a liquid crystal with a comparatively smaller transverse dipole moment on the same alignment layer. The experimental results clearly demonstrate the competition between a short-range dipolar force and long-range van der Waals force at the interfacial region. Using discontinuous anchoring transition in the sample, we demonstrate a possible bistable device for memory and light-driven display.
Collapse
Affiliation(s)
- Surajit Dhara
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1-S8-42 O-okayama, Meguro-ku, Tokyo 152-8552, Japan.
| | | | | | | | | | | | | |
Collapse
|
16
|
Barbero G, Dahl I, Komitov L. Nonmonotonic behavior of the nematic tilt angle in a temperature-induced surface transition. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:052701. [PMID: 18643116 DOI: 10.1103/physreve.77.052701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2008] [Revised: 04/10/2008] [Indexed: 05/26/2023]
Abstract
We report on a nonmonotonic temperature behavior of the pretilt in cells containing polymers as alignment layers. The latter are very promising since they enable control of the anchoring of the liquid crystal. We show that such a behavior cannot be interpreted by the standard Landau or mean-field theory. We propose a generalization of the mean-field model, including the temperature dependence of the anchoring due to the polymer layer that enables a description of the nonlinear behavior. The agreement between the predictions of the model and the experimental data is good.
Collapse
Affiliation(s)
- Giovanni Barbero
- Liquid Crystal Physics, Department of Physics, University of Gothenburg, SE-412 96, Gothenburg, Sweden
| | | | | |
Collapse
|
17
|
Gabovich AM, Reznikov YA, Voitenko AI. Excess nonspecific Coulomb ion adsorption at the metal electrode/electrolyte solution interface: role of the surface layer. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:021606. [PMID: 16605349 DOI: 10.1103/physreve.73.021606] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Revised: 01/05/2006] [Indexed: 05/08/2023]
Abstract
Excess ion adsorption gamma induced by the polarization image forces in the system of a metal electrode/symmetric electrolyte solution separated by an insulating interlayer has been calculated. The adopted theoretical scheme involves the Coulomb Green's function in a three-layer system with sharp interfaces and specular reflection at them. The influence of the spatial dispersion of the dielectric permittivities epsilon(i)(k) in all the three media on the image force energy W(im) and the adsorption gamma has been analyzed, where k is the wave vector. A comparison with the classical model, where epsilon(i)=const, has been carried out. It has been shown that both the Debye-Hückel ion screening and the spatial dispersion of the solvent contribution epsilon(solv)(k) to the overall dielectric function epsilon(el)(k) of the electrolyte solution lead to the qualitative difference with the results for the classical model. In particular, in a wide range of ion concentrations n0 a thin interlayer L > or = 5-10 angstroms effectively screens out the attractive influence of the metallic electrode, so that the net Coulomb adsorption may become repulsive. The approach and the results obtained qualitatively describe two physically different situations. Specifically, the introduced interlayer corresponds either to the dense near-electrode (inner) electrolyte layer or to the intentionally deposited control coating of arbitrary thickness.
Collapse
Affiliation(s)
- A M Gabovich
- Institute of Physics, National Academy of Sciences of Ukraine, 46 Nauka Ave., Kyiv 03028, Ukraine
| | | | | |
Collapse
|
18
|
Ree M. High performance polyimides for applications in microelectronics and flat panel displays. Macromol Res 2006. [DOI: 10.1007/bf03219064] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
19
|
Lednei MF, Pinkevich IP. Threshold spatially periodic structure of the director in a nematic flexoelectric cell with finite anchoring energy. CRYSTALLOGR REP+ 2005. [DOI: 10.1134/1.1927612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
20
|
Lee SW, Lee SJ, Hahm SG, Lee TJ, Lee B, Chae B, Kim SB, Jung JC, Zin WC, Sohn BH, Ree M. Role of the n-Alkyl End of Bristles in Governing Liquid Crystal Alignment at Rubbed Films of Brush Polymer Rods. Macromolecules 2005. [DOI: 10.1021/ma047856z] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Seung W. Lee
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Seong J. Lee
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Seok G. Hahm
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Taek J. Lee
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Byeongdu Lee
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Boknam Chae
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Seung B. Kim
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Jin C. Jung
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Wang C. Zin
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Byeong H. Sohn
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| | - Moonhor Ree
- Polymer Research Institute, Department of Chemistry, Division of Molecular and Life Sciences, BK21 Program, and Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790−784, Republic of Korea
| |
Collapse
|
21
|
Gosselin P, Mohrbach H. Free-energy formalism for particle adsorption. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:031101. [PMID: 15903400 DOI: 10.1103/physreve.71.031101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2004] [Indexed: 05/02/2023]
Abstract
The equilibrium properties of particle adsorption is investigated theoretically. The model relies on a free-energy formulation which allows us to generalize the Maxwell-Boltzmann description to solutions for which the bulk volume fraction of potentially adsorbed particles is very high. As an application we consider the equilibrium physical adsorption of neutral and charged particles from solution onto two parallel adsorbing surfaces.
Collapse
Affiliation(s)
- Pierre Gosselin
- Université Grenoble I, Institut Fourier, UMR 5582 CNRS-UJF, UFR de Mathématiques, BP74, Saint Martin d'Hères, France
| | | |
Collapse
|
22
|
Scalerandi M, Pagliusi P, Cipparrone G, Barbero G. Influence of the ions on the dynamical response of a nematic cell submitted to a dc voltage. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:051708. [PMID: 15244838 DOI: 10.1103/physreve.69.051708] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2004] [Indexed: 05/24/2023]
Abstract
The influence of the ions present in a liquid crystal on the dynamical response of a nematic slab submitted to a dc voltage is studied. The evolution of the system toward the equilibrium state is investigated by solving the continuity equation for the electric charge, taking into account the current of drift and of diffusion. Our analysis shows that the formation of the double layers close to the electrodes strongly modifies the distribution of the electric field across the sample. We evaluate the surface polarization due to the ions movements and the contribution to the anisotropic part of the surface energy having a dielectric origin. We show also that, even if the optical response of the liquid crystal is a slow phenomenon, the distribution of the ionic charge is rather fast. Consequently, the presence of the ions cannot be neglected in the determination of the flexoelectric coefficients when the nematic sample is submitted to a square wave having a period of the order of 1 s.
Collapse
Affiliation(s)
- M Scalerandi
- Dipartimento di Fisica del Politecnico di Torino, and INFM, UdR di Torino Politecnico, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy
| | | | | | | |
Collapse
|
23
|
Barbero G, Olivero D, Scaramuzza N, Strangi G, Versace C. Influence of the bias-voltage on the anchoring energy for nematic liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:021713. [PMID: 14995475 DOI: 10.1103/physreve.69.021713] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2003] [Indexed: 05/24/2023]
Abstract
The influence of the bias-voltage on the anisotropic part of the nematic surface energy is analyzed. The experimental data show a strong dependence of the anchoring strength on the bias-voltage when the electrodes of the nematic cell are covered with WO3. The observed dependence can be interpreted taking into account the ions dissolved in the liquid crystal. We propose a model in which the effect of the bias-voltage is to collect the ions near the electrodes, in a surface layer whose thickness is of the order of the Debye's screening length. The surplus of electric field due to this ions confinement gives rise to an electrostatic contribution to the total energy that can be considered as a surface energy. The proposed model is in good agreement with the experimental data. The model is used to interpret the observed independence of the anchoring strength on the bias-voltage when the (indium-tin-oxide) electrode is covered with a film of polyimide, or it is without any covering. The influence of a charge emission from the electrodes under the bias voltage on the anchoring energy is also analyzed. Possible applications of the observed phenomenon are discussed.
Collapse
Affiliation(s)
- G Barbero
- Dipartimento di Fisica del Politecnico di Torino, and INFM, Unità di Ricerca di Torino Politecnico, Corso Duca degli Abruzzi 24, 10129 Turin, Italy
| | | | | | | | | |
Collapse
|
24
|
Chae B, Lee SW, Lee B, Choi W, Kim SB, Jung YM, Jung JC, Lee KH, Ree M. Sequence of Rubbing-Induced Molecular Segmental Reorientations in the Nanoscale Film Surface of a Brush Polymer Rod. J Phys Chem B 2003; 107:11911-6. [DOI: 10.1021/jp034955q] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Boknam Chae
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Seung Woo Lee
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Byeongdu Lee
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Wooyoung Choi
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Seung Bin Kim
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Young Mee Jung
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Jin Chul Jung
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Kyung Hoon Lee
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Moonhor Ree
- Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| |
Collapse
|
25
|
Pereira HA, Batalioto F, Evangelista LR. Contribution of the ionic adsorption phenomenon to the effective anchoring energy of a nematic liquid-crystal sample. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:040701. [PMID: 14682916 DOI: 10.1103/physreve.68.040701] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Indexed: 05/24/2023]
Abstract
The effective anchoring energy resulting from the ionic adsorption phenomenon in a nematic liquid-crystal sample in the shape of a slab of thickness d is investigated. The electric field distribution is determined in the framework of a general nonlinear Poisson-Boltzmann approach. The analysis is particularized for the case in which d>>lambdaD, where lambdaD is the Debye screening length. In this limit, the spatially dependent electric field distribution across the sample as well as the contribution, of dielectric and flexoelectric origins, to the effective anchoring energy is obtained in an exact manner.
Collapse
Affiliation(s)
- H A Pereira
- Departamento de Física, Universidade Estadual de Maringá, Avenida Colombo, 5790, 87020-900 Maringá, Paraná, Brazil
| | | | | |
Collapse
|
26
|
Shioda T, Wen B, Rosenblatt C. Continuous nematic anchoring transition due to surface-induced smectic order. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:041706. [PMID: 12786376 DOI: 10.1103/physreve.67.041706] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2002] [Indexed: 05/24/2023]
Abstract
A continuous transition from tilted to homeotropic alignment at an interface is observed at a temperature T(a) for a nematic liquid crystal on cooling toward the nematic-smectic-A phase transition temperature. T(a) is found to depend on the treatment of the substrate. The behavior is examined theoretically in terms of a pair of competing easy axes (homeotropic and planar) and the tilt elasticity associated with the growth of surface-induced smectic order.
Collapse
Affiliation(s)
- Tatsutoshi Shioda
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079, USA
| | | | | |
Collapse
|
27
|
Chae B, Kim SB, Lee SW, Kim SI, Choi W, Lee B, Ree M, Lee KH, Jung JC. Surface Morphology, Molecular Reorientation, and Liquid Crystal Alignment Properties of Rubbed Nanofilms of a Well-Defined Brush Polyimide with a Fully Rodlike Backbone. Macromolecules 2002. [DOI: 10.1021/ma020639i] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Boknam Chae
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Seung Bin Kim
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Seung Woo Lee
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Sang Il Kim
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Wooyoung Choi
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Byeongdu Lee
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Moonhor Ree
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Kyung Hoon Lee
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| | - Jin Chul Jung
- Department of Chemistry, BK21 Functional Polymer Thin Film Group, Center for Integrated Molecular Systems, Polymer Research Institute, Department of Materials Science & Engineering, and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea
| |
Collapse
|
28
|
Olivero D, Evangelista LR, Barbero G. External electric-field effect on nematic anchoring energy. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:031721. [PMID: 11909095 DOI: 10.1103/physreve.65.031721] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2001] [Indexed: 05/23/2023]
Abstract
The influence of an external field on the effective anchoring energy of a nematic liquid crystal in contact with a substrate is theoretically analyzed. Our analysis is performed on the hypothesis that the electrodes are perfectly blocking and that there is no selective ion adsorption. The proposed theory predicts an effective anchoring energy dependent on the applied dc voltage. According to the sign of the dielectric anisotropy and of the flexoelectric coefficient the dependence of the anchoring energy strength with the bias can be monotonic or not. For large bias voltage the effective anchoring energy strength tends to a constant value. Our theory is in qualitative agreement with published data investigating the influence of the bias on the saturation voltage.
Collapse
Affiliation(s)
- D Olivero
- Dipartimento di Fisica del Politecnico and INFM, Corso Duca degli Abruzzi, 24-10129 Torino, Italy
| | | | | |
Collapse
|
29
|
Barbero G, Olivero D. Ions and nematic surface energy: beyond the exponential approximation for the electric field of ionic origin. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:031701. [PMID: 11909075 DOI: 10.1103/physreve.65.031701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2001] [Indexed: 05/23/2023]
Abstract
We present a general model to describe the influence of the ionic adsorption on the anisotropic part of the surface energy of a nematic liquid crystal in contact with a substrate. We show that in the limit of small adsorption energy, the exponential approximation for the electric field of ionic origin works well. In this limit, the dielectric and flexoelectric contributions to the surface energy are quadratic and linear on the density of adsorbed ions, respectively. In the opposite limit of large adsorption energy, the exponential approximation for the electric field does not work, and the two contributions to the surface energy are both found to depend linearly on the surface density of adsorbed charges. Approximated formulas reported in literature are derived from our general equations as particular cases, and their limits discussed. An expression for the surface polarization in nematic liquid crystal due to the ionic adsorption is also deduced. Our analysis is performed in the framework of the Poisson-Boltzmann theory, where dimensionless ions are treated within a mean field approach. Possible extensions of our model are indicated.
Collapse
Affiliation(s)
- G Barbero
- Dipartimento di Fisica del Politecnico di Torino, and INFM, Unità di Recerca di Torino Politecnico, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
| | | |
Collapse
|
30
|
van der Vegt NFA, Müller-Plathe F, Geleßus A, Johannsmann D. Orientation of liquid crystal monolayers on polyimide alignment layers: A molecular dynamics simulation study. J Chem Phys 2001. [DOI: 10.1063/1.1415498] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
31
|
Evangelista LR, Barbero G. Adsorption phenomenon and external field effect on an isotropic liquid containing impurities. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:021101. [PMID: 11497556 DOI: 10.1103/physreve.64.021101] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2001] [Indexed: 05/23/2023]
Abstract
The steady-state distribution of ionic charges in a liquid, in the presence of surface adsorption, is determined. The effect of an electric field applied by means of blocking electrodes is considered. The analysis shows that the surface adsorption of ions dissolved in the liquid is responsible for an asymmetry in the electric-field distribution. In the model, the liquid is assumed to be dielectric but to contain impurities. These impurities, by means of a chemical reaction, can bring about ions. The theory takes into account the activation energy for the ionization chemical reaction and the adsorption energy of the ions at the surface.
Collapse
Affiliation(s)
- L R Evangelista
- Dipartimento di Fisica del Politecnico and INFM, Corso Duca degli Abruzzi, 24-10129 Torino, Italy
| | | |
Collapse
|
32
|
Barbero G, Jägemalm P, Zvezdin AK. Temperature-induced surface transition in nematic liquid crystals oriented by evaporated SiOx. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:021703. [PMID: 11497604 DOI: 10.1103/physreve.64.021703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2000] [Revised: 03/22/2001] [Indexed: 05/23/2023]
Abstract
Temperature induced surface transitions observed in nematic liquid crystals oriented by obliquely evaporated SiOx are analyzed. It is shown that the experimental data can be interpreted with a theory for the thermal renormalization of the anisotropic part of the surface energy based on the mean field approximation. By assuming that the nematic scalar order parameter is given by the Maier-Saupe theory, the fit is obtained with only one free parameter. The temperature behaviors of the polar and azimuthal angles are in agreement with the proposed model over the whole temperature range.
Collapse
Affiliation(s)
- G Barbero
- Dipartimento di Fisica del Politecnico di Torino and Istituto Nazionale di Fisica della Materia, INFM, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
| | | | | |
Collapse
|
33
|
Weiss K, Wöll C, Johannsmann D. Orientation of thin liquid crystal films on buffed polyimide alignment layers: A near-edge x-ray absorption fine structure investigation. J Chem Phys 2000. [DOI: 10.1063/1.1287908] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
34
|
Barbero G, Zvezdin AK. Thermal renormalization of the anchoring energy of nematic liquid crystals. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:6711-21. [PMID: 11102023 DOI: 10.1103/physreve.62.6711] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2000] [Indexed: 11/07/2022]
Abstract
The temperature dependence of the anchoring energy of a nematic liquid crystal on thermal fluctuations is studied. We consider the weak anchoring case, where the interaction of a nematic molecule on the surface with the substrate is small with respect to the mean field energy due to the other nematic molecules. The analysis is performed by means of a perturbation method in which the expansion parameter is the surface interaction. The presented model is valid for any value of the scalar order parameter. We show that the renormalization of the anchoring coefficients due to thermal fluctuations is proportional to the generalized scalar order parameters. We show also that, at the lowest order in the scalar order parameter, Landau-like theories agree with our mean field approach. An expression for the thermal renormalization of the anchoring coefficients valid in the low temperature region, where the fluctuations are small, is derived. The agreement between our theoretical predictions and the experimental data obtained by other groups is fairly good over a large temperature range.
Collapse
Affiliation(s)
- G Barbero
- Dipartimento di Fisica del Politecnico di Torino, and Istituto di Fisica della Materia, Unita di Ricerca Torino Politecnico, Corso Duca degli Abruzzi 24, I-10129 Torino, Italia and Joint Laboratory of Orientationally Ordered Materials (OOM-Lab)
| | | |
Collapse
|
35
|
Nazarenko VG, Pergamenshchik VM, Koval'chuk OV, Nych AB, Lev BI. Non-Debye screening of a surface charge and a bulk-ion-controlled anchoring transition in a nematic liquid crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:5580-3. [PMID: 11970434 DOI: 10.1103/physreve.60.5580] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/1999] [Indexed: 04/18/2023]
Abstract
We study the anchoring mechanism due to substrate-adsorbed ions by examining a related anchoring transition. An analytical solution to the Poisson equation shows that, as their number suffices for a non-negligible anchoring contribution, the surface field is screened over some characteristic microscopic distance. It is shown both theoretically and experimentally that the critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions.
Collapse
Affiliation(s)
- V G Nazarenko
- Institute of Physics, Prospect Nauki 46, Kyiv-22, 252022 Ukraine.
| | | | | | | | | |
Collapse
|
36
|
Poniewierski A, Samborski A. Anchoring transitions in the nematic‐substrate system: Study of the Landau–de Gennes model. J Chem Phys 1996. [DOI: 10.1063/1.472603] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
37
|
Crawford GP, Ondris-Crawford RJ, Doane JW, Zumer S. Systematic study of orientational wetting and anchoring at a liquid-crystal-surfactant interface. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:3647-3661. [PMID: 9964675 DOI: 10.1103/physreve.53.3647] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
|
38
|
Faetti S, Riccardi M. Elestic constants in the interfacial layer at the nematic-liquid-crystal-vapour interface. ACTA ACUST UNITED AC 1995. [DOI: 10.1007/bf02456790] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
39
|
Zhu YM, Lu ZH, Wei Y. Relation between anchorings of liquid crystals and conformation changes in aligning agents by the Langmuir-Blodgett film technique investigation. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 51:418-422. [PMID: 9962659 DOI: 10.1103/physreve.51.418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
|