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 nanoparticlepolymer 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