Effective Viscosity of Polymer Films on a Strongly Slipping Surface

We have studied the thickness (h₀) dependence of effective viscosity (η_eff) of entangled polystyrene (PS) supported by a polydimethylsiloxane (PDMS) layer grafted on silica -- a representative of polymer film systems exhibiting strong slippage. Our result shows that η_eff was independence of the polymer molecular weight, consistent with plug flow. However, a ~h₀² scaling was found instead of the ~h₀ dependence expected. A theoretical model based on flow dynamics dominated by low-density elastic pinning sites and strong slippage is described that explains the observation.