Stability and breakup of thin polar films on coated substrates: relationship to macroscopic parameters of wetting

Abstract

We study the linear and nonlinear stability, dynamics, and lifetimes of ultrathin (<100 nm) apolar and polar fluid films on uncoated and coated nonwettable substrates. The dynamics of nonequilibrium microscopic films is correlated to the equilibrium macroscopic parameters of wetting for coating and substrate. The equilibrium wettability (contact angle) of a coated substrate is determined almost entirely by coating properties. However, for films much thicker than the coating, the length scale of the instability is governed largely by the apolar surface properties of the substrate regardless of the apolar and polar properties of the coating. The film breakup time is more sensitive to the coating properties even for relatively thick films. The apolar and polar interactions with the coating control the instability of relatively thin films. For polar films, the actual (nonlinear) time of rupture may be several orders of magnitude smaller than the predictions of the linear theory.