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.

• Received 22 December 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.165701