Thickness and Composition Dependence of the Glass Transition Temperature in Thin Homogeneous Polymer Blend Films

Abstract

Nowadays there is much interest in thin polymer
\nfilms due to their importance in science and technology.
\nStudies on Tg in thin polymer films have revealed that
\nit is dependent on film thickness and that such dependence
\nincreases with decreasing film thickness. As
\nfor the case where the interaction between the polymer
\nand the substrate is not large enough to affect the glass
\ntransition, Tg usually decreases with decreasing thickness.
\nOn the other hand, Tg of films coated on a
\nstrongly favorable substrate increased with decreasing
\nfilm thickness due to a strong interaction between
\npolymer and substrate. Although many experimental
\nworks have been performed on Tg in typical homopolymer
\nthin films, there has been no work dealing with
\npolymer blend systems. The concept of physically blending
\ntwo or more existing polymers to obtain new
\nproducts has been attracting widespread interest and
\ncommercial utilization.14 This blending method can be
\nused as a good way to control the basic properties of
\npolymers without sacrificing many attractive properties
\nof each polymer. One of the most attractive compatible
\nblends is that of poly(2,6-dimethyl-1,4-phenylene oxide)
\n(PPO) and polystyrene (PS). Perhaps the most unambiguous
\ncriterion of polymer compatibility is the detection
\nof a single glass transition temperature whose
\ntemperature is intermediate between those corresponding
\nto the two-component polymers. For the bulk blend
\nsystems, PPO and PS are known to be compatible in
\nall compositions.
\nIn this study, to find out the thickness dependence of
\nTg depression in the compatible PPO and PS blend thin
\nfilms, the Tgs of the films are measured as functions of
\nthickness (200-1200 Å) and composition and compared