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 and kinetics of a pressure-induced order−disorder transition (ODT) in a solvated diblock copolymer. We find that birefringence is an excellent technique to measure the order−disorder transition at high pressure, yielding sharp changes in its intensity at the transition. Small-angle neutron scattering exhibits a corresponding change in the width of the scattering peak at the ODT. Both techniques indicate a nearly linear increase of the ODT temperature as a function of pressure. The combination of pressure as a controlling thermodynamic variable and birefringence as the measurement tool permits short time scale kinetics experiments. We find the time scale of the disordering process to be significantly shorter than the ordering time, as revealed by profound asymmetries 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.