Effect of sample preparation on the glass-transition of thin polystyrene films

We have investigated the effect of sample preparation on the glass-transition temperature (T-g) of thin films of polystyrene (PS). By preparing and measuring the glass-transition temperature T-g of multilayered polymer films, we are able to assess the contribution of the spincoating process to the reduced T-g values often reported for thin PS films. We find that it is possible to determine a T-g even on the first heating cycle, and that by the third heating cycle (a total annealing time of 15 min at T = 393 K) the T-g value has reached a steady state. By comparing multilayered versus single layered films we find that the whole T-g depends only on the total film thickness, and not on the thickness of the individual layers. These results strongly suggest that the spincasting process does not contribute significantly to T-g reductions in thin polymer films. (C) 2004 Wiley Periodicals, Inc.