PYROELECTRIC AND ELECTROOPTICAL EFFECTS IN THE SMC-ASTERISK PHASE OF A POLYSILOXANE LIQUID-CRYSTAL

The pyroelectric coefficient, the spontaneous polarization P-s, the optical tilt angle theta, and the switching time of a polysiloxane liquid crystalline polymer have been measured. The pyroelectric coefficient is found to be one order of magnitude greater and the response broader than for a low molar liquid crystal reported in the literature and is comparable to that of the solid ferroelectrics. P-s vs theta is found to be nonlinear, and the ratio of P-s/theta shows anomalies close to the SmC*-SmA transition temperature. The measurements of theta and the optical response time are used to calculate the switching time which spans from 1 to 100 ms, depending on the temperature. The optical response time in the SmA phase close to the SmC*-SmA transition temperature, together with a finite value of the pyroelectric coefficient, provide evidence of a SmC* phase induced by an external field. The rotational viscosity as a function of temperature shows critical behavior at the SmC*-SmA phase transition temperature.