STATIC AND KINETIC-STUDY OF A PRESSURE-INDUCED ORDER-DISORDER TRANSITION - BIREFRINGENCE AND NEUTRON-SCATTERING

We utilize birefringence and neutron scattering to study the statics a nd kinetics of a pressure-induced order-disorder transition (ODT) in a solvated diblock copolymer. We find that birefringence is an excellen t technique to measure the order-disorder transition at high pressure, yielding sharp changes in its intensity at the transition. Small-angl e neutron scattering exhibits a corresponding change in the width of t he scattering peak at the ODT. Both techniques indicate a nearly Linea r increase of the ODT temperature as a function of pressure. The combi nation of pressure as a controlling thermodynamic variable and birefri ngence as the measurement tool permits short time scale kinetics exper iments. We find the time scale of the disordering process to be signif icantly shorter than the ordering time, as revealed by profound asymme tries in the response of the system upon pressurization compared with depressurization. Disordering times as small as 0.5 s are observed in rapid pressure drop experiments.