Molecular Weight Dependence Manuscript

MOLECULAR WEIGHT DEPENDENCE OF REDUCTIONS IN THE GLASS TRANSITION TEMPERATURE OF THIN, FREELY STANDING POLYMER FILMS

K. Dalnoki-Veress, J.A. Forrest, C. Murray, C. Gigault and John Dutcher
Phys. Rev. E 63, 031801-1 - 031801-10 (2001).

ABSTRACT

We have used transmission ellipsometry to perform a comprehensive study of the glass transition temperature T_g of freely-standing polystyrene films. Six molecular weights M_w, ranging from 575 X 10³ to 9100 X 10³, were used in the study. For each M_w value, large reductions in T_g (as much as 80 ^oC below the bulk value) were observed as the film thickness h was decreased. We have studied in detail the dependence of the T_g reductions on M_w in a regime dominated by chain confinement effects. The empirical analysis presented is highly suggestive of the existence of a mechanism of mobility in thin freely-standing films that is inhibited in the bulk and distinct from the usual cooperative motion associated with the glass transition.