Internal Phase Separation Induces Dewetting in Multicomponent Polymer Films

Thin liquid films that dewet from their substrate are ubiquitous as demonstrated by the beading of paint on oily surface. Although most coatings contain more than one component, the dewetting mechanisms in multicomponent films are not understood. Using dPMMA:SAN (50:50) films (550 nm) with or without nanoparticles (NP), we demonstrate, for the first time, that the Laplace pressure induced by internal phase-separated structure is the driving force for roughening and rupture in polymer blend films. Three NP were investigated, namely NP$_{A}$, NP$_{B}$, and NP$_{C}$ which either partition into dPMMA or weakly and strongly segregate to the dPMMA/SAN interface, respectively. NP$_{B}$ are more effective than NP$_{A}$ at stabilizing the film, whereas NP$_{C}$ are able to prevent film rupture. Upon annealing, roughened films display a periodic, lacey structure, resembling patterns from spinodal dewetting. The fluctuation periodicity scales with roughness evolution as \textit{$\lambda $}$_{s} \quad \propto \quad R_{q}^{1/4}$ for neat blends and blends with NP$_{A}$, whereas the scaling breaks down for blends containing NP$_{B}$ and NP$_{C}$. These studies show that phase separation is responsible for film roughening.