Viscosity and Surface-Promoted Slippage of Thin Polymer Films Supported by a Solid Substrate

• DOI: 10.1021/acs.macromol.5b01002
• Publication Date: 2015-07-09T17:14:00Z
• Authors: Fei Chen; Dongdong Peng; Chi-Hang Lam; Ophelia K. C. Tsui
• Keywords: 01 natural sciences; 0104 chemical sciences

Thermally activated flow dynamics of polystyrene films supported by silicon is studied for a wide range of film thickness (h0) and molecular weights (Mw). At low Mw, the effective viscosity of the nanometer thin films is smaller than the bulk and decreases with decreasing h0. This is due to enhancement of the total shear flow by the augmented mobility at the free surface. As Mw increases, with h0 becoming smaller than the polymer radius of gyration (Rg), the effective viscosity switches from being substrate-independent to substrate-dependent. We propose that interfacial slippage then dominates and leads to plug flow. The friction coefficient is found to increase with h0 providing h0/Rg < ∼1, demonstrating a surface-promoted confinement effect.