Published Research - Department of Chemistry

 

Date of this Version

December 1999

Comments

Published by American Institute of Physics. J. Chem. Physics VOLUME 111, NUMBER 22, 8 DECEMBER 1999. ©1999 American Institute of Physics. Permission to use. http://jcp.aip.org/.

Abstract

Ordering in Langmuir monolayer mesophases is examined using an approach based on the elastic theory of crystals. Molecular tails are modeled as ‘‘defects’’ grafted onto a two-dimensional elastic medium and are characterized by elastic dipoles. It is assumed that disorder in the parent, LS, phase is due to competition between local (within a domain) and global (hexagonal arrangement of domains) structure. By treating the LS phase as a mixture of rectangular and/or oblique domains (rectangular and/or oblique defects within the two-dimensional elastic medium), density fluctuations due to elastic interactions between domains are analyzed. The correlation function for the elastic dipoles is calculated and the elastic interactions’ renormalization of the elastic properties of mesophases is analyzed. Results are shown to be compatible with very recent experiments on microscopic and macroscopic elasticity of the monolayers as well as those on positional disorder in LS and S phases. Kinetic aspects of the elastic response are considered, as is the contribution of the elastic domains’ reorientations to x-ray diffuse scattering.

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