Temperature Step Dewetting Method for Determination of T$_{\mathrm{g}}$ Dependence on Thickness for Linear and Star Branched Polystyrene*

The current liquid dewetting study is an extension of work previously presented by Bodiguel and Fretigny [Phys. Rev. Lett., \textbf{97}, (2006)] and Wang and McKenna [J. Polym. Sci., Part B: Polym. Phys., \textbf{51}, (2013)]. The liquid dewetting method consists of floating a thin polymer film on a liquid (glycerol) substrate. The film shrinks in a homothetic way while the thickness increases. The current goal is to obtain the glass transition temperature T$_{\mathrm{g}}$ as a function of thickness h for low and high molecular weight linear polystyrene (PS), long branched 3 arm star PS, and short and long branched 8 arm star PS. In the normal dewetting method and in pseudo-thermodynamic methods a new sample is required to obtain the T$_{\mathrm{g}}$ vs. h for each individual thickness. The temperature step dewetting technique can be used to obtain the T$_{\mathrm{g}}$ vs h dependence using one single thin polymer film with initial known thickness h$_{\mathrm{o}}$. Thereby, obtaining rapidly the same information that would have required multiple individual tests. The T$_{\mathrm{g}}$ reductions are compared to previously presented liquid dewetting results, as well as those for supported and freely standing polystyrene thin films.