Nonequilibrium polymer rheology in spin-cast films.

A new experimental approach is introduced to probe the rheology of >or=100 nm-thick liquid polymer films. As-cast films were found to have a substantially reduced effective viscosity compared to annealed films. The reduced viscosity is explained in terms of nonequilibrium chain conformations giving rise to a reduced entanglement density caused by the rapid quenching of the film during spin coating. Unexpectedly long annealing times at high temperatures are required for the films to recover their bulk rheology.