Experimental evidence for a new parameter to control the glass transition of confined polymers

Polymer nanocomposites can be used to study confinement effects on the polymer glass transition temperature (T-g) in a controlled manner by varying interparticle spacing. Using gold nanoparticles in polymethylmethacrylate, we show how the polymer T-g can be tuned by variation of the nanoparticle-polymer interface width (sigma), keeping interparticle spacing fixed. We report the first experimental observation of a crossover in the sign of T-g deviation for confined polymers by variation of sigma and propose a model to explain the dependence of crossover width on the spatial extent of cooperatively rearranging regions.