PROBING THE ELECTRIC-FIELD ALIGNMENT OF A THERMOTROPIC LIQUID-CRYSTALLINE POLYMER BY SYNCHROTRON-RADIATION

The orientation of a cyclic side-chain thermotropic liquid crystalline material in an AC field was monitored in real-time using synchrotron radiation. Monitoring the realignment processes in the millisecond-to- minute time-scale was made possible by the high X-ray flux. Orientatio n parameters and response times were calculated asa function of temper ature and frequency. Response times decreased exponentially with tempe rature due to a decrease in the viscosity. Very little dependence of t he response time on frequency was observed, except at low temperatures , where a switch from homeotropic to planar alignment of the molecules was detected. This reorientation of the director was studied in real- time and the resulting complex diffraction patterns were due to equal but opposite director rotations from an alignment parallel to the appl ied electric field to an alignment perpendicular to the applied electr ic field. The orientation parameters were highest in the central porti on of the mesophase temperature range. At temperatures near clearing, the net degree of orientation diminished. Cooling through the mesophas e with an applied electric field resulted in much larger orientation p arameters than could be obtained by aligning at a fixed temperature in the mesophase.