Document Detail

Direct Nanomechanical Measurement of an Anchoring Transition in a Nematic Liquid Crystal Subject to Hybrid Anchoring Conditions.
MedLine Citation:
PMID:  22621655     Owner:  NLM     Status:  Publisher    
We have used a surface forces apparatus to measure the normal force between two solid curved surfaces confining a film of nematic liquid crystal (5CB, 4'-n-pentyl-4-cyanobiphenyl) under hybrid planar-homeotropic anchoring conditions. Upon reduction of the surface separation D, we measured an increasingly repulsive force in the range D = 35-80 nm, reaching a plateau in the range D = 10-35 nm, followed by a short-range oscillatory force at D < 5 nm. The oscillation period was comparable to the cross-sectional diameter of the liquid crystal molecule and characteristic of a configuration with the molecules parallel to the surfaces. These results show that the director field underwent a confinement-induced transition from a splay-bend distorted configuration at large D, which produces elastic repulsive forces, to a uniform planar nondegenerate configuration with broken homeotropic anchoring, which does not produce additional elastic forces as D is decreased. These findings, supported by measurements of the birefringence of the confined film at different film thicknesses, provide the first direct observation of an anchoring transition on the nanometer scale.
Marina Ruths; Bruno Zappone
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-5-23
Journal Detail:
Title:  Langmuir : the ACS journal of surfaces and colloids     Volume:  -     ISSN:  1520-5827     ISO Abbreviation:  -     Publication Date:  2012 May 
Date Detail:
Created Date:  2012-5-24     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882736     Medline TA:  Langmuir     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Department of Chemistry, University of Massachusetts Lowell , Lowell, Massachusetts 01854, United States.
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