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Lorenz A, Agra-Kooijman DM, Zimmermann N, Kitzerow HS, Evans DR, Kumar S. Bilayers in nanoparticle-doped polar mesogens. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:062505. [PMID: 24483466 DOI: 10.1103/physreve.88.062505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Indexed: 06/03/2023]
Abstract
Structures of the mesophases of five members of the 4-n-alkyl-4'-cyanobiphenyl homologous series (4-n-butyl-4'-cyanobiphenyl to 4-n-octyl-4'-cyanobiphenyl) doped with milled BaTiO_{3} nanoparticles were investigated by x-ray scattering. Clear solutions of each of the 4-n-alkyl-4'-cyanobiphenyls were first prepared in n-heptane and then doped with an n-heptane/nanoparticle dispersion, which led to gelation. The nanogels were found to be one-dimensional, multilayered, smectic nanostructures in each case. Surprisingly, a characteristic layer spacing of 4.5 nm was observed in all five homologues. Synchrotron x-ray scattering study of the multilayer structures of doped 4-n-pentyl-4'-cyanobiphenyl and 4-n-octyl-4'-cyanobiphenyl revealed nine orders of the primary Bragg reflection which were used to calculate the electron density profiles of the multilayers by Fourier analysis. The multilayers were found to consist of molecular bilayers wherein the mesogens were arranged in a head-to-head assembly of the polar head groups. The alkyl tails of the mesogenic molecules were freely movable and the tail-to-tail assembly was stabilized by heptane. The dissolved nanoparticles clearly induced a new self-assembled nanostructure in which the rigid aromatic part, and not the overall length, of the molecules defined the layer spacing.
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Affiliation(s)
- Alexander Lorenz
- Department of Engineering, University of Cambridge, 9 JJ Thompson Avenue, CB3 0FA Cambridge, United Kingdom
| | | | - Natalie Zimmermann
- Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany
| | - Heinz-S Kitzerow
- Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany
| | - Dean R Evans
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA
| | - Satyendra Kumar
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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Lorenz A, Zimmermann N, Kumar S, Evans DR, Cook G, Kitzerow HS. Doping the nematic liquid crystal 5CB with milled BaTiO3 nanoparticles. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:051704. [PMID: 23214802 DOI: 10.1103/physreve.86.051704] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 09/21/2012] [Indexed: 06/01/2023]
Abstract
The simple nematic mesogen 5CB was doped with milled BaTiO3 nanoparticles and was investigated with x-ray scattering. Doping with BaTiO3 nanoparticles of 9 nm in diameter led to the formation of crystallites. These crystallites precipitated and formed a waxlike nanodispersion of 5CB and nanoparticles, which led to intense x-ray scattering signals characteristic of a multilayer structure. Surprisingly, the multilayers possess unusual interlayer spacing, which cannot be explained by simple smectic order of the calamitic molecules.
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Affiliation(s)
- Alexander Lorenz
- Department of Chemistry, University of Paderborn, Warburger Strasse 100, Paderborn 33098, Germany
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Yaroshchuk O, Reznikov Y. Photoalignment of liquid crystals: basics and current trends. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c1jm13485j] [Citation(s) in RCA: 403] [Impact Index Per Article: 33.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Relaix S, Leheny RL, Reven L, Sutton M. Memory effect in composites of liquid crystal and silica aerosil. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:061705. [PMID: 22304107 DOI: 10.1103/physreve.84.061705] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Indexed: 05/31/2023]
Abstract
Aerosil silica nanoparticles dispersed in a liquid crystal (LC) possess the interesting property of keeping memory of an electric- or magnetic-field-induced orientation. Two types of memory have been identified: thermally erasable memory arising from the pinning of defect lines versus a "permanent" memory where the orientation persists even after thermal cycling the samples up to the isotropic phase. To address the source of the latter type of memory, solid-state nuclear magnetic resonance spectroscopy and conventional x-ray diffraction (XRD) were first combined to characterize the LC orientational order as a function of multiple in-field temperature cycles. Microbeam XRD was then performed on aligned gels of different concentrations to gain knowledge of the structural properties at the origin of the memory effect. No detectable anisotropy of the gel or significant breaking of silica strands with heating ruled out the formation of an anisotropic silica network as the source of the permanent memory as previously proposed. Instead, support for a role of the surface memory effect, well known for planar substrates, in stabilizing the permanent memory was deduced from "training" of the composites, that is, optimizing the orientational order through the thermal in-field cycling. The ability to train the composites is inversely proportional to the strength of the random-field disorder. The portion of thermally erasable memory also decreases as the silica density increases. We propose that the permanent memory originates from the surface memory effect operating at points of intersection in the silica network. These areas, where the LC is strongly confined with conflicted surface interactions, are trained to achieve an optimized orientation and subsequently act as sites from which the LC orientational order regrows after zero-field thermal cycling up to the isotropic phase.
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Affiliation(s)
- Sabrina Relaix
- Department of Physics, McGill University, Montreal, Quebec, Canada H3A 2T8
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Yoon HG, Kang SW, Dong RY, Marini A, Suresh KA, Srinivasarao M, Kumar S. Nematic biaxiality in a bent-core material. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:051706. [PMID: 20866246 DOI: 10.1103/physreve.81.051706] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 02/21/2010] [Indexed: 05/29/2023]
Abstract
The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at ∼149 °C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on 13C chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149 °C. Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le [Phys. Rev. E 79, 030701 (2009)].
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Affiliation(s)
- Hyung Guen Yoon
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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Zola RS, Lenzi EK, Evangelista LR, Barbero G. Memory effect in the adsorption phenomena of neutral particles. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:042601. [PMID: 17500940 DOI: 10.1103/physreve.75.042601] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Revised: 12/21/2006] [Indexed: 05/15/2023]
Abstract
The adsorption-desorption phenomenon of neutral particles dissolved in an isotropic fluid is investigated by using a nonsingular kernel in the kinetic equation at the limiting surfaces. To account for the relevance of a memory effect, three types of kernels in the kinetic equation are considered. Similar kernels have been used to investigate nonexponential relaxation including several contexts such as dielectric relaxation, diffusion-controlled relaxation in liquids, liquid crystals, and amorphous polymers. A suitable choice for a temporal kernel can account for the relative importance of physisorption or chemisorption, according to the time scale governing the adsorption phenomena, and can be the key mechanism to understand the specific roles of both processes. By using a general procedure, the time evolution of the density of particles is determined in closed analytical form. The analysis is relevant in the description of the adsorption phenomena in general.
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Affiliation(s)
- R S Zola
- Departamento de Física, Universidade Estadual de Maringá, Avenida Colombo 5790, 87020-900 Maringá, Paraná, Brazil
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Shi Y, Martinez-miranda LJ, Kumar S. X-Ray Scattering Study of a Smectic-A Liquid Crystal Partially Confined Between Free Surface and Microgrooved Substrates. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259708041750] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Yushan Shi
- a Department of Physics and Liquid Crystal Institute , Kent State University , Kent , OH , 44242 , USA
| | - L. J. Martinez-miranda
- a Department of Physics and Liquid Crystal Institute , Kent State University , Kent , OH , 44242 , USA
- b Department of Materials and Nuclear Engineering , University of Maryland , College Park , MD , 20742 , USA
| | - Satyendra Kumar
- a Department of Physics and Liquid Crystal Institute , Kent State University , Kent , OH , 44242 , USA
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Zhou YW, Gilpin RK. FT-IR Studies of the Interfacial Alignment of the Liquid Crystal 4′-Cyano-4-biphenyl[4-(4-pentenyloxy)] benzoate Bonded to Silica. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259808045519] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Y. W. Zhou
- a College of Science and Mathematics, Wright State University , Dayton , OH , 45435
- b Hoechst Celanese Corporation, Technical Center , Corpus Christie , TX , 18409
| | - R. K. Gilpin
- a College of Science and Mathematics, Wright State University , Dayton , OH , 45435
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Kocevar K, Blinc R, Musevic I. Atomic force microscope evidence for the existence of smecticlike surface layers in the isotropic phase of a nematic liquid crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:R3055-R3058. [PMID: 11088877 DOI: 10.1103/physreve.62.r3055] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2000] [Indexed: 05/23/2023]
Abstract
Using a temperature controlled atomic force microscope we have observed presmectic layering in the isotropic phase of 4-cyano-4(')-n-octylbiphenyl (8CB) on silanated glass. The first molecular layer shows a smecticlike compressibility modulus of B approximately 10(7) N/m(2) and is stable more than 20 K beyond the bulk clearing point. It is followed by a presmectic modulation that increases when cooling towards the isotropic-nematic transition. In the bulk isotropic phase, the layers cover approximately 70% of the glass surface, indicating a clusterlike organization.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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Zalar B, Zumer S, Finotello D. Deuteron NMR study of monolayer thick films of nematogenic molecules. PHYSICAL REVIEW LETTERS 2000; 84:4866-4869. [PMID: 10990818 DOI: 10.1103/physrevlett.84.4866] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/1999] [Indexed: 05/23/2023]
Abstract
We present a deuteron NMR study of molecular thickness films of a nematogenic material in cylindrical pores. Compared to liquid crystal in bulk or completely filling the pores, a reduced quadrupole splitting is found. It strongly depends on thickness, but only weakly on temperature, even crossing the bulk nematic-isotropic transition. This demonstrates the presence of a 2D-like film that eventually coexists with a bulklike phase suggesting a dewetting behavior. Motionally averaged angular patterns with biaxiallike features reveal unexpectedly fast surface molecular diffusion.
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Affiliation(s)
- B Zalar
- J. Stefan Institute, University of Ljubljana, Jamova 39, 1000 Ljubljana, Slovenia
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Kotov NA, Haraszti T, Turi L, Zavala G, Geer RE, Dékány I, Fendler JH. Mechanism of and Defect Formation in the Self-Assembly of Polymeric Polycation−Montmorillonite Ultrathin Films. J Am Chem Soc 1997. [DOI: 10.1021/ja964409t] [Citation(s) in RCA: 225] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- N. A. Kotov
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - T. Haraszti
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - L. Turi
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - G. Zavala
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - R. E. Geer
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - I. Dékány
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
| | - J. H. Fendler
- Contribution from the Department of Chemistry, University of Oklahoma, Stillwater, Oklahoma 74078, Department of Chemistry and the W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100, Department of Colloid Chemistry, Attila József University, Szeged H-6720, Aradi V.t.1, Hungary, and Department of Physics, State University of New York at Albany, Albany, New York 12222
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Growth modes of organic semiconductor thin films using organic molecular beam deposition: epitaxy, van der Waals epitaxy, and quasi-epirtaxy. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s0968-5677(96)00053-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Richetti P, Moreau L, Barois P, Kékicheff P. Measurement of the interactions between two ordering surfaces under symmetric and asymmetric boundary conditions. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:1749-1762. [PMID: 9965253 DOI: 10.1103/physreve.54.1749] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Cull B, Shi Y, Kumar S, Shih R, Mann J. X-ray reflectivity study of interface roughness, structure, and morphology of alignment layers and thin liquid crystal films. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 51:526-535. [PMID: 9962671 DOI: 10.1103/physreve.51.526] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Moreau L, Richetti P, Barois P. Direct Measurement of the Interaction between Two Ordering Surfaces Confining a Presmectic Film. PHYSICAL REVIEW LETTERS 1994; 73:3556-3559. [PMID: 10057413 DOI: 10.1103/physrevlett.73.3556] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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