Estimation of the thickness dependence of the glass transition temperaturein various thin polymer films

The glass transition temperature (T-g) in the thin poly(alpha-methyl styren e) and polysufone films that are coated on the surface of a Si wafer is inv estigated in this paper. A novel. equation was suggested to estimate the th ickness dependence of T-g in thin films. Ellipsometry has been used to meas ure T-g of various thin films as functions of sample thickness, molecular w eight, and kind of polymer. One adjustable parameter in the equation, i.e., xi, was obtained from fitting this function with the experimentally measur ed T-g. The magnitude of the fitted parameter xi showed discrepancies betwe en the polymer types but similarity between the molecular weights. This par ameter xi corresponded to the statistical segment length of the polymer. Al l the measured T-g data of the investigated polymers were superimposed in o ne curve by normalizing the thickness and the measured T-g with the paramet er xi and bulk T-g, respectively. The origin of T-g depression phenomena in thin films was closely correlated with its segmental length and not with w hole chain size.