Electric-field-induced molecular reorientation dynamics by near-field scanning optical microscopy

Daniel A. Higgins; Erwen Mei; Xiangmin Liao

doi:10.1117/12.350633

17 June 1999 Electric-field-induced molecular reorientation dynamics by near-field scanning optical microscopy

Daniel A. Higgins, Erwen Mei, Xiangmin Liao

Proceedings Volume 3607, Scanning and Force Microscopies for Biomedical Applications; (1999) https://doi.org/10.1117/12.350633
Event: BiOS '99 International Biomedical Optics Symposium, 1999, San Jose, CA, United States

Abstract

A new technique developed in this laboratory and based on near-field scanning optical microscopy (NSOM) is used to study the field-induced reorientation of molecules in local regions of thin film materials. A highly concentrated electric field is applied across the sample, between the metal-coated near-field probe and the sample substrate. Molecular motion induced in the sample by modulation of the electric field is observed using NSOM methods. Lock-in detection of the optical response to a sinusoidally- modulated field, recorded under cross-polarized, transmitted-light conditions allows for the recording of dynamics images. The local rate of reorientation is measured for individual locations in a sample by recording the response in either the time or frequency domains. Dynamics information is obtained with microsecond(s) ec time resolution and nanometer-scale spatial resolution. This method is applied in studies of polymer-dispersed liquid crystal films. In these materials, small droplets of nematic liquid crystal are dispersed in an otherwise uniform poly(vinyl alcohol) film. The liquid crystal droplets are birefringent, forming electrically-switchable light-scattering centers. A simple forced-oscillator model for the reorientation dynamics in the liquid crystal is presented. Variations in the time scale and extent of molecular reorientation are observed as a function of field strength, droplet size, droplet shape, and position probed. The data are interpreted based on knowledge of the important intermolecular forces active in these materials.

Citation Download Citation

Daniel A. Higgins, Erwen Mei, and Xiangmin Liao "Electric-field-induced molecular reorientation dynamics by near-field scanning optical microscopy", Proc. SPIE 3607, Scanning and Force Microscopies for Biomedical Applications, (17 June 1999); https://doi.org/10.1117/12.350633

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