INTERFACE AND SURFACE EFFECTS ON THE GLASS-TRANSITION IN THIN POLYSTYRENE FILMS

Lifetime analysis of positronium annihilating in nanometer voids is us ed to study the thermal expansion behavior of thin, Si-supported polys tyrene films near the glass transition temperature T-g. A reduction in void volume expansion is correlated with a reduction in the apparent T-g as film thickness decreases. Our results can be fitted using a thr ee-layer model incorporating a 50 Angstrom constrained layer at the Si interface and a 20 Angstrom surface region with reduced T-g.