Self-destruction and dewetting of thin polymer films: the role of interfacial tensions

Abstract

We present real-time optical microscopy observations of the pattern evolution in self-destruction and subsequent dewetting of thin polymer films based on experiments with polydimethylsiloxane films sandwiched between silicon wafers and aqueous surfactant solutions. A clear scenario consisting of four distinct stages has been identified: amplification of surface fluctuations, break-up of the film and formation of holes, growth and coalescence of holes, and droplet formation and ripening. Besides a linear dependence on film viscosity and surface tension, the time τ for film rupture varied significantly with film thickness h(t ˜ h⁵), as expected from theory. While the role of long-range forces is dominant only in the first stage, the later stages are controlled by the combination of interfacial tensions resulting in the contact angle characterizing the three-phase contact line. During the first stage, the characteristic distance of the pattern remains constant, represented by a time-independent wavevector. In all subsequent stages, this wavevector decreases with time as a consequence of hole opening, coalescence, and ripening on droplets. The later stages of evolution are a function of the contact angle at the three-phase contact line. Only a clear distinction between stages before and after film break-up allows a correct interpretation of the observed pattern evolution in unstable thin films.