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

Abstract

We present real-time optical microscopy observations of the pattern evolution inself-destruction and subsequent dewetting of thin polymer films based on experimentswith polydimethylsiloxane films sandwiched between silicon wafers and aqueoussurfactant solutions. A clear scenario consisting of four distinct stages has beenidentified: amplification of surface fluctuations, break-up of the film and formationof holes, growth and coalescence of holes, and droplet formation and ripening.Besides a linear dependence on film viscosity and surface tension, the time τfor film rupture varied significantly with film thicknessh (τ ∼ h5),as expected from theory. While the role of long-range forces is dominant only inthe first stage, the later stages are controlled by the combination of interfacialtensions 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 afunction of the contact angle at the three-phase contact line. Only a cleardistinction between stages before and after film break-up allows a correctinterpretation of the observed pattern evolution in unstable thin films.