Dielectric relaxation spectroscopy and alignment behavior of a polymer-dispersed liquid crystal and its component materials

The dielectric properties of a polymer-dispersed liquid crystal (PDLC), a l iquid-crystal (LC) mixture (BL036), and three polymer matrices of PN314 con taining different amounts of BL036 were determined over a range of frequenc ies and temperatures and, for the LC and PDLC, over a range of voltages lea ding to homeotropic alignment of the LC. The overall dielectric relaxation process was a weighted sum of contributions from (1) the primary (delta) pr ocess in the LC arising from the motions of the dipoles about the short mol ecular axis and (2) dipole motions in the polymer matrix. The dielectric sp ectra were determined as a function of frequency, temperature, and, when ap propriate, applied voltage. An equivalent electrical circuit was used as a working model to describe the dielectric behavior of the PDLC in the absenc e and presence of applied voltages. Agreement between the dielectric data a nd this model was achieved if a portion of the LC phase at the interface wa s assumed to be immobile. The director order parameter for the LC component in the PDLC was determined from dielectric measurements as the material wa s aligned homeotropically in an applied electric field. (C) 2001 John Wiley & Sons, Inc.