We determined the low-shear effective viscosity of entangled polystyrene thin film melts, in the thickness range of $27<h<\mathrm{}100\mathrm{}\mathrm{nm},$ on ${\mathrm{SiO}}_x/\mathrm{Si}$ substrates. This was accomplished using a method based on the notion that thin liquid films can become unstable and rupture due to defects or to destabilizing, long-range van der Waals interactions (dewetting). The holes that are created in the film subsequently grow at a rate determined by a balance between the capillary driving forces and the viscous resistive forces. Based on the velocity of growth of holes on the substrate, we show that the viscosity decreases appreciably with decreasing thickness for $25<h<\mathrm{}50\mathrm{}\mathrm{nm}.$ These results are consistent with studies which suggest that the glass transition of entangled polystyrene thin film melts on ${\mathrm{SiO}}_x/\mathrm{Si}$ substrates exhibit an apparent decrease with decreasing film thickness over the same range of h.

• Received 15 August 2001

DOI:https://doi.org/10.1103/PhysRevE.65.031806