Orientational Transitions of Liquid Crystals Driven by Binding of

Langmuir 2003, 19, 275-284

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Orientational Transitions of Liquid Crystals Driven by Binding of Organoamines to Carboxylic Acids Presented at Surfaces with Nanometer-Scale Topography Rahul R. Shah† and Nicholas L. Abbott* Department of Chemical Engineering, University of Wisconsin, Madison 1415 Engineering Drive, Madison, Wisconsin 53706 Received May 26, 2002. In Final Form: October 1, 2002 We recently reported that the orientations of nematic phases of 4-cyano-4′-pentylbiphenyl (5CB), when supported on surfaces with nanometer-scale topography and oriented carboxylic acid groups, are strongly influenced by n-H2N(CH2)5CH3 bound to these surfaces. The changes in orientation of the liquid crystals were found to be triggered by amounts of bound n-H2N(CH2)5CH3 that were not measurable by optical methods such as ellipsometry (ellipsometric thicknesses 70 kJ/mol).17 We hypothesized that disruption of the shortranged interaction between the 5CB and COOH groups on the surface would likely lead to a change in the orientation of the liquid crystal. In a preliminary communication,20 we have confirmed that binding of n-H2N(CH2)5CH3 to surfaces presenting carboxylic acid groups does lead to a measurable change in the orientation of 5CB. The changes in orientation of the liquid crystal were found to be triggered by amounts of bound n-H2N(CH2)5CH3 that were not measurable by using optical methods such as ellipsometry (ellipsometric thicknesses