94.
Glass transition temperatures (
Tg) of thin poly(styrene-co-methyl methacrylate) and poly(2-vinyl pyridine-co-styrene) films coated on a native oxide surface of Si wafer (100) were measured by ellipsometry. The thickness dependence of
Tg can be properly fitted by previously suggested equation developed for homopolymers, based upon a continuous multi-layer model, although one component in thin random copolymer films demonstrates a slightly favorable interaction between a substrate and thin film, and another demonstrates a strongly favorable interaction. Surface and interface have a strong influence on
Tg of thin film coated on substrate: the surface has the effect of reducing
Tg, whereas the interface increases the
Tg according to the degree of interaction between a substrate and thin film. This degree of interaction can be quantified as an interaction parameter (
k), and is dependent on the composition of random copolymers. For the estimation of
k values of thin random copolymer films, we proposed a parallel type additive function (1/
kran=
w1/
k1+
w2/
k2) where
w is a weight fraction of component.
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