Instabilities in thin polymer films: From pattern formation to rupture

Thermal fluctuations of the surfaces of thin polymer films can be amplified by the long-range van der Waals or dispersion force which acts across the film. When freely-standing polymer films are heated, this instability leads to the formation of holes. We have measured the formation and growth of ho les in very thin, freely-standing polystyrene (PS) films to learn about the mobility of the confined polymer molecules. We have also symmetrically cap ped freely-standing PS films with thin, solid layers to probe the effects o f mechanical confinement. Aggressive annealing of the trilayer films produc es a novel in-plane morphology which can be understood in terms of the bala nce between the decrease in free energy associated with the dispersion inte raction and the increase in free energy associated with the bending of the capping layers. The general nature of the morphology, and its reversibility , is demonstrated.