A theoretical model on the basis of the free‐volume concept is presented explaining the temperature dependence of photoinduced birefringence in polystyrene films that contain Disperse Red‐1. Birefringence increases with temperature up to 180 K as the free volume for isomerization increases, and then decreases as thermally activated processes dominate. The fast process of birefringence decay has a time constant that increases with temperature at low temperatures, due to the change in photoisomerization.
Temperature dependence of the birefringence amplitude measured at 300 s. The amplitude increases with temperature up to 180 K and then decreases. The solid line is for guiding the eye.
