A direct quantitative measure of surface mobility in a glassy polymer

Abstract

Thin polymer films have striking dynamical properties that differ from their bulk counterparts. With the simple geometry of a stepped polymer film on a substrate, we probe mobility above and below the glass transition temperature $T_{\text{g}}$. Above $T_{\text{g}}$ the entire film flows, while below $T_{\text{g}}$ only the near surface region responds to the excess interfacial energy. An analytical thin film model for flow limited to the free surface region shows excellent agreement with sub-$T_{\text{g}}$ data. The system transitions from whole film flow to surface localized flow over a narrow temperature region near the bulk $T_{\text{g}}$. The experiments and model provide a measure of surface mobility in a sample geometry where confinement and substrate effects are negligible. This fine control of the glassy rheology is of key interest to nanolithography among numerous other applications.

References in corpus (1)

• Free surface flows with large slopes: beyond lubrication theory

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