Document Detail


Wetting of liquid-crystal surfaces and induced smectic layering at a nematic-liquid interface: an x-ray reflectivity study.
MedLine Citation:
PMID:  18517395     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
We report the results of a synchrotron x-ray reflectivity study of bulk liquid-crystal surfaces that are coated by thin wetting films of an immiscible liquid. The liquid-crystal subphase consisted of the nematic or isotropic phase of 4-octyl- 4;{'} -cyanobiphenyl (8CB), and the wetting film was formed by the fluorocarbon perfluoromethylcyclohexane (PFMC), a volatile liquid. The thickness of the wetting film was controlled by the temperature difference DeltaT(micro) between the sample and a reservoir of bulk PFMC, contained within the sealed sample cell. Phase information on the interfacial electron density profiles has been extracted from the interference between the scattering from the PFMC-vapor interface and the surface-induced smectic order of the 8CB subphase. The liquid-crystal side of the nematic-liquid (8CB-PFMC) interface is characterized by a density oscillation whose period corresponds to the smectic layer spacing and whose amplitude decays exponentially toward the underlying nematic subphase. The decay length xi of the smectic amplitude is independent of the PFMC film thickness but increases as the nematic-smectic- A transition temperature T(NA) is approached, in agreement with the longitudinal correlation length xi(parallel) proportional, variant(T-T(NA))(-0.7} for the smectic fluctuations in the bulk nematic. The results indicate that the homeotropic orientation of the 8CB molecules is preferred at the 8CB-PFMC interface and that the observed temperature dependence of the smectic layer growth is consistent with the critical adsorption mechanism. The observed DeltaT(micro) dependence of the PFMC film thickness, L proportional, variant(DeltaT(micro))(-1/3) , implies that PFMC completely wets the 8CB surface and is dominated by the nonretarded dispersion interactions between hydro- and fluorocarbons. The complete wetting behavior of PFMC is nearly independent of the degree of interfacial smectic order in the subphase.
Authors:
Masafumi Fukuto; Oleg Gang; Kyle J Alvine; Benjamin M Ocko; Peter S Pershan
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Publication Detail:
Type:  Journal Article     Date:  2008-03-14
Journal Detail:
Title:  Physical review. E, Statistical, nonlinear, and soft matter physics     Volume:  77     ISSN:  1539-3755     ISO Abbreviation:  Phys Rev E Stat Nonlin Soft Matter Phys     Publication Date:  2008 Mar 
Date Detail:
Created Date:  2008-06-03     Completed Date:  2008-08-25     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101136452     Medline TA:  Phys Rev E Stat Nonlin Soft Matter Phys     Country:  United States    
Other Details:
Languages:  eng     Pagination:  031607     Citation Subset:  -    
Affiliation:
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA. fukuto@bnl.gov
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