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Title: In situ prepared polymer films as alignment layers for nematic liquid crystals

Abstract

By means of UV-visible irradiations and convenient photoinitiators, we realize the cross-linked polymerization of a triacrylate monomer in solution in a nematic liquid crystal (p-pentyl-p{sup '}-cyanobiphenyl) at low concentrations (a few wt %), i.e., under conditions opposite to the synthesis of polymer-dispersed liquid crystals. As atomic force microscope measurements show, when operating close to, but below, the percolation transition, a thin polymer layer is synthesized in situ, directly covering and coating all the substrate. These observations therefore confirm that the properties of anchoring and of alignment memory previously observed in such nematic cells effectively originate from the synthesized polymer film. According to the photoinitiator used, bulk or surface polymerizations dominate and respectively produce continuous or discontinuous films (i.e., with separate clusters). In the former case, polymer aggregates are first synthesized. They then diffuse in the volume until they meet a surface, where they definitely stick if they are large enough. An estimate of the entropy and interaction energy differences between the two states, stuck or free, shows that the aggregates stick on the substrates if their size exceeds the length of about three monomers, i.e., if they contain more than 20-30 monomers. Interestingly, these films may be used to replicatemore » nonuniform alignment patterns that are difficult to realize otherwise. The method may be considered as an imprinting method.« less

Authors:
;  [1]
  1. Institut de Physique et Chimie des Materiaux de Strasbourg, 23 rue du Loess, 67034 Strasbourg (France)
Publication Date:
OSTI Identifier:
20884954
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 100; Journal Issue: 12; Other Information: DOI: 10.1063/1.2405735; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACRYLATES; ATOMIC FORCE MICROSCOPY; ENTROPY; FILMS; LAYERS; LIQUID CRYSTALS; MONOMERS; POLYMERIZATION; POLYMERS; SOLUTIONS; SUBSTRATES

Citation Formats

Pires, David, and Galerne, Yves. In situ prepared polymer films as alignment layers for nematic liquid crystals. United States: N. p., 2006. Web. doi:10.1063/1.2405735.
Pires, David, & Galerne, Yves. In situ prepared polymer films as alignment layers for nematic liquid crystals. United States. https://doi.org/10.1063/1.2405735
Pires, David, and Galerne, Yves. 2006. "In situ prepared polymer films as alignment layers for nematic liquid crystals". United States. https://doi.org/10.1063/1.2405735.
@article{osti_20884954,
title = {In situ prepared polymer films as alignment layers for nematic liquid crystals},
author = {Pires, David and Galerne, Yves},
abstractNote = {By means of UV-visible irradiations and convenient photoinitiators, we realize the cross-linked polymerization of a triacrylate monomer in solution in a nematic liquid crystal (p-pentyl-p{sup '}-cyanobiphenyl) at low concentrations (a few wt %), i.e., under conditions opposite to the synthesis of polymer-dispersed liquid crystals. As atomic force microscope measurements show, when operating close to, but below, the percolation transition, a thin polymer layer is synthesized in situ, directly covering and coating all the substrate. These observations therefore confirm that the properties of anchoring and of alignment memory previously observed in such nematic cells effectively originate from the synthesized polymer film. According to the photoinitiator used, bulk or surface polymerizations dominate and respectively produce continuous or discontinuous films (i.e., with separate clusters). In the former case, polymer aggregates are first synthesized. They then diffuse in the volume until they meet a surface, where they definitely stick if they are large enough. An estimate of the entropy and interaction energy differences between the two states, stuck or free, shows that the aggregates stick on the substrates if their size exceeds the length of about three monomers, i.e., if they contain more than 20-30 monomers. Interestingly, these films may be used to replicate nonuniform alignment patterns that are difficult to realize otherwise. The method may be considered as an imprinting method.},
doi = {10.1063/1.2405735},
url = {https://www.osti.gov/biblio/20884954}, journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 12,
volume = 100,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}