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17 June 1999 Electric-field-induced molecular reorientation dynamics by near-field scanning optical microscopy
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Proceedings Volume 3607, Scanning and Force Microscopies for Biomedical Applications; (1999)
Event: BiOS '99 International Biomedical Optics Symposium, 1999, San Jose, CA, United States
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.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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);

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