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We report the first measurements of the glass transition temperature T₆ for thin freely standing polystyrene (PS) films. We have used Brillouin light scattering to measure T₆ for freely standing films of different thicknesses. We find that T₆ decreases linearly with film thickness h for h700, with a reduction of 70 K for a film with h0ex{0ex}=0ex{0ex}290. These measurements characterize unambiguously the effects of the free surface on T₆ of thin polymer films. Results are compared to similar results for supported PS films Keddie et al. , Europhys. Lett. 27, 59 (1994), and we find that their measured values are influenced strongly by the substrate.
Forrest et al. (Mon,) studied this question.
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