Abstract

We use a custom-built uniaxial tensile tester together with dark-field optical microscopy to study how nanoscale confinement affects the mechanical failure of glassy polymer films. By independently varying film thickness (10–150 nm) and molecular weight (61–2135 kDa) for polystyrene, we separate the individual contributions of chain entanglement density and enhanced surface chain mobility to the failure behavior of ultrathin films, providing a clearer picture of why very thin polymer films become more brittle as they are confined.