Hole formation and growth in freely standing polystyrene films

Using optical microscopy, we have measured the formation and growth of hole s in freely standing poly styrene films in the melt state. For all films, w e observed exponential growth of the hole radius and uniform thickening. Ou r measurements are interpreted in terms of the dependence of the viscosity on the shear strain rate associated with the hole growth process. The measu rement of hole growth in thin freely standing polymer films provides a uniq ue probe of nonlinear viscoelastic effects in confined polymers. [S1063-651 X(99)11002-X].