SIZE-DEPENDENT DEPRESSION OF THE GLASS-TRANSITION TEMPERATURE IN POLYMER-FILMS

The glass transition temperature of thin polystyrene films has been me asured as a function of film thickness. It is found that the glass tra nsition decreases in temperature as the thickness of the film is reduc ed. The effect is not strongly molecular-weight dependent, ruling out chain confinement as the major cause; instead we suggest that at the s urface of the glassy film a liquidlike layer exists whose size diverge s as the glass transition temperature is approached from below.