Dewetting Pathways and Morphology of Unstable Thin Liquid Bilayers

Abstract

Three-dimensional long-wave nonlinear analysis of the instabilities engendered by van der Waals forces in a thin (<100 nm) viscous bilayer resting on a rigid substrate is presented. The bilayers are classified based on the macroscopic dewetting behavior of the films, and the three-dimensional morphological evolutions of the films are studied in each case. The dewetting of the bilayers is initiated by one of the two basic modes at the interfaces: in-phase "bending" and out-of-phase "squeezing". We show that the thicknesses, surface energies, and viscosities of the films have significant influence on the mode selection, pathway, of dewetting, and the final morphology of dewetting. Different equilibrium morphologies are obtained by tuning the nature and the strength of the intermolecular forces present at the films, which include: (i) an array of channels and ridges in the lower layer with the upper liquid embedded inside the channels, (ii) islands in the lower layer with the upper layer embedded in the interstitial spaces, and (iii) the lower layer droplets encapsulated by the upper layer.