Case II Diffusion in Polystyrene Fiber: In-situ Measurement of a Moving Sharp Front

Abstract

In-situ measurement of a moving sharp front formed in a polystyrene fiber- organic vapor system was presented by using optical microscopy and light scattering technique. The diffusion of acetone vapor with the relative vapor pressure of 0.92 into the physically aged polystyrene fiber of 25 μm diameter was measured at 25°C. The system showed following characteristics; (1) an induction time, (2) formation of a sharp front after the induction time, (3) nearly constant rate of the sharp advancing front, (4) step-like distribution of the penetrant concentration at the sharp front, (5) uniform state of swelling behind the sharp front. These findings strongly suggested Case II diffusion. The effect of the physical aging on the polymer glass to get front formation was also discussed based on Thomas and Windle model.