Influence of residual stress on dewetted morphology of spin coated polymer thin films

Spontaneous instability in polymer thin film leading to its rupture and subsequent formation of polymer droplets is called Dewetting. In this regard, it is essential to investigate the fundamental properties of polymer leading to dewetting and its effect on the dewetted morphology. We report the dependence of dewetted morphology of polymer thin film on residual stress generated during spin coating. Unlike applied stress, residual stress arises due to polymer chain entanglement while the polymer is in solution state and endures high centripetal force. The spin-coated polymer film is at a metastable equilibrium state generating a residual stress among the polymer chains. We produce different residual stress in polymer thin film of same thickness by spin coating at different rotation speeds. Based on the degree of stress present, the dynamics of dewetting as well as morphology varies. From this we exhibit the contrast by dewetting the thin film by different techniques: Thermal annealing, solvent vapor and good solvent mediated dissolution. The contrast in the morphology is shown as a measure of droplet periodicity (λ_D) and diameter (D_D). Consequently, we can qualitatively predict the degree of residual stress in thin film by its dewetted morphology without further characterization.