Electric-field-induced ion migration in polymer-dispersed liquid-crystal films observed by near-field scanning optical microscopy

Abstract

Near-field scanning optical microscopy (NSOM) is used to study electric-field-induced ion migration in polymer-dispersed liquid-crystal (PDLC) films. An electric field is applied between the aluminum-coated NSOM probe and an optically transparent, conductive glass substrate, upon which the film is supported. Electric-field-induced reorientation of the liquid crystal beneath the probe is observed optically. PDLC films doped with tetraalkylammonium tetrafluoroborate salts show dramatically different reorientation dynamics than those prepared without ionic dopants. The behavior observed is attributed to the charging of double layers at the polymer/liquid-crystal interface that cancel the field within the "bulk" of the liquid crystal in time. Observation of subsequent liquid-crystal relaxation yields a measure of the local ion migration rate. © 1999 American Institute of Physics.