Direct experimental evidences of the density variation of ultrathin polymer films with thickness

Beyond the peculiar glass transition temperature (Tg) studied extensively for over two decades, we have investigated in this work variation of mass density polymer thin films, a key property barely put forward literature. We were able to directly measure polystyrene (PS) and poly (methyl methacrylate) (PMMA) films as function their thickness from accurate Quartz Crystal Microbalance (QCM) dissolution experiments. Depending on chemical nature polymers, results showed an unambiguous when film was reduced: increase PS decrease PMMA films. In last part, measured coefficient thermal expansion (CTE) both polymers rationalize apparent inconsistency increase/decrease with commonly observed depression/rise Tg PS/PMMA Surprisingly, similar thickness, pointing out clear correlation between temperature, free volume polymer.