Abstract
We have examined the direct effect of manipulating the number of free surfaces on the measured glass transition temperature of thin polystyrene films. Thin films in the range with molecular weights of and were studied. Ellipsometry was used to determine the temperature dependence of the thickness and refractive index of freestanding films. By noting the change in slope in each of these quantities, a value can be assigned in quantitative agreement with previously reported results. For thin freestanding films this value is reduced from that of the bulk. The exact same films are then transferred to a Si substrate and the of the resulting supported film was determined. The values of the now supported films are the same as the bulk value and the same as previous reports of similar supported films. These experiments unambiguously show that free interfaces are the dominant cause of the reductions for the film thicknesses studied.
- Received 8 May 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.055701
© 2012 American Physical Society