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Title: Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes

Abstract

The swelling of main chain liquid crystalline polymers (LCPs) in good nematic solvents is theoretically studied, focusing on brushes of terminally anchored, grafted LCPs. The analysis is concerned with long LCPs, of length L, with n[sub 0] >> 1 hairpin defects. The extension behavior of the major axis, R[parallel], of these ellipsoidal objects gives rise to an Ising elasticity with a free energy penalty of F[sub el](R[parallel])/kT [approx] n[sub 0] [minus] n[sub 0](1 [minus] R[parallel][sup 2]/L[sup 2])[sup 1/2]. The theory of the extension behavior enables the formulation of a Flory type theory of swelling of isolated LCPs yielding R[parallel] [approx] exp(2U[sub h]/5kT)N[sup 3/5] and R [perpendicular] [approx] exp([minus]U[sub h]/10kT)N[sup 3/5], with N the degree of polymerization and U[sub h] the hairpin energy. It also allows the generalization of the Alexander model for polymer brushes to the case of grafted LCPs. The behavior of LCP brushes depends on the alignment imposed by the grafting surface and the liquid crystalline solvent. A tilting phase transition is predicted as the grafting density is increased for a surface imposing homogeneous, parallel anchoring. A related transition is expected upon compression of a brush subject to homeotropic, perpendicular alignment. The effect of magnetic or electric fieldsmore » on these phase transitions is also studied. The critical magnetic/electric field for the Frederiks transition can be lowered to arbitrarily small values by using surfaces coated by brushes of appropriate density.« less

Authors:
 [1];  [2]
  1. College de France, Paris (France). Lab. de Physique de la Matiere Condensee
  2. Univ. of California, Santa Barbara, CA (United States). Dept. of Materials
Publication Date:
OSTI Identifier:
6186007
DOE Contract Number:  
FG03-87ER45288
Resource Type:
Journal Article
Journal Name:
Macromolecules; (United States)
Additional Journal Information:
Journal Volume: 26:16; Journal ID: ISSN 0024-9297
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; POLYMERS; CRYSTAL STRUCTURE; CRYSTAL-PHASE TRANSFORMATIONS; ELECTRIC FIELDS; LIQUID CRYSTALS; MAGNETIC FIELDS; POLYMERIZATION; CHEMICAL REACTIONS; CRYSTALS; FLUIDS; LIQUIDS; PHASE TRANSFORMATIONS; 360602* - Other Materials- Structure & Phase Studies

Citation Formats

Williams, D R.M., and Halperin, A. Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes. United States: N. p., 1993. Web. doi:10.1021/ma00068a022.
Williams, D R.M., & Halperin, A. Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes. United States. https://doi.org/10.1021/ma00068a022
Williams, D R.M., and Halperin, A. 1993. "Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes". United States. https://doi.org/10.1021/ma00068a022.
@article{osti_6186007,
title = {Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes},
author = {Williams, D R.M. and Halperin, A},
abstractNote = {The swelling of main chain liquid crystalline polymers (LCPs) in good nematic solvents is theoretically studied, focusing on brushes of terminally anchored, grafted LCPs. The analysis is concerned with long LCPs, of length L, with n[sub 0] >> 1 hairpin defects. The extension behavior of the major axis, R[parallel], of these ellipsoidal objects gives rise to an Ising elasticity with a free energy penalty of F[sub el](R[parallel])/kT [approx] n[sub 0] [minus] n[sub 0](1 [minus] R[parallel][sup 2]/L[sup 2])[sup 1/2]. The theory of the extension behavior enables the formulation of a Flory type theory of swelling of isolated LCPs yielding R[parallel] [approx] exp(2U[sub h]/5kT)N[sup 3/5] and R [perpendicular] [approx] exp([minus]U[sub h]/10kT)N[sup 3/5], with N the degree of polymerization and U[sub h] the hairpin energy. It also allows the generalization of the Alexander model for polymer brushes to the case of grafted LCPs. The behavior of LCP brushes depends on the alignment imposed by the grafting surface and the liquid crystalline solvent. A tilting phase transition is predicted as the grafting density is increased for a surface imposing homogeneous, parallel anchoring. A related transition is expected upon compression of a brush subject to homeotropic, perpendicular alignment. The effect of magnetic or electric fields on these phase transitions is also studied. The critical magnetic/electric field for the Frederiks transition can be lowered to arbitrarily small values by using surfaces coated by brushes of appropriate density.},
doi = {10.1021/ma00068a022},
url = {https://www.osti.gov/biblio/6186007}, journal = {Macromolecules; (United States)},
issn = {0024-9297},
number = ,
volume = 26:16,
place = {United States},
year = {Mon Aug 02 00:00:00 EDT 1993},
month = {Mon Aug 02 00:00:00 EDT 1993}
}