Measurement of the cross relaxation rate for a polymer dispersed liquid crystal system

Abstract

Proton cross relaxation between liquid crystal and polymer in a polymer dispersed liquid crystal (PDLC) system has been studied by the use of magic angle spinning and polarization transfer. The cross relaxation rates have been determined as functions of temperature, irradiation power, and off-resonance frequency setting. The data at each temperature are treated by a new set of relaxation equations which are not limited by the assumption of complete saturation of the polymer protons. The cross relaxation rates for the aromatic and aliphatic protons are similar over the temperature range studied, indicating that the liquid crystal molecules anchor parallel to the polymer surface. Before the glass transition, the cross relaxation rates increase with temperature due to a reduction in the contact time. After the glass transition, at about 37 °C, the cross relaxation rates decrease rapidly with temperature due to an increase in the motions of the polymer molecules which cause a reduction in the efficiency of spin energy exchange.