Dynamic light scattering in solid polymers

Abstract The viscosity of an amorphous polymeric solid above its glass transition [T g (T,P)] increases as the temperature of the solid is decreased or the pressure is increased. Under changes in temperature or pressure, molecular subunits in the polymeric solid undergo configurational changes. Such changes or relaxations have a distribution of relaxation strengths and times. As the solid is cooled or as the hydrostatic pressure on the solid is increased, the relaxation strengths increase and the relaxation times increase. These changes in relaxation or dynamic properties are very dramatic as the empirical T g is approached. Near T g the polymeric solid is no longer in volume equilibrium; continued cooling or pressuring at a time rate faster than the average relaxation time will produce a polymeric glass. This glass is a nonequilibrium, amorphous solid. If the glass is held at a fixed temperature and pressure very close to, but below, T g , the volume of the glass will be observed to relax to its equilibrium value. For temperatures and pressures well below T g , equilibrium is a much more conjectural concept since the relaxation times become extremely long. It has been proposed1,2 that there is a characteristic temperature T g at which an amorphous polymer undergoes a second-order transition to an equilibrium glass with zero configurational entropy (i.e., a noncrystallizable solid).