Impact of interfacial slip on the stability of liquid two-layer polymer films

Abstract

In this work we derive systems of coupled thin-film equations for immiscible liquid polymer layers on a solid substrate. We take into account slip between liquids and solids and also slip between both liquids. On the scale of tens of nanometres, such two-layer systems are susceptible to instability and may rupture and dewet due to intermolecular forces. The stability of the two-layer system and its significant dependence on the order of magnitude of slip is investigated via these thin-film models. With weak slip at both the liquid–liquid and liquid–solid interfaces and polymer layers of comparable thickness, the dispersion relation typically shows two local maxima, one in the long-wave regime and the other at moderate wavenumbers. The former is associated with perturbations that mainly affect the gas–liquid interface and the latter with larger relative perturbation amplitudes at the liquid–liquid interface. Increasing the slip at the liquid–liquid interface generally favours the long-wave regime and can in fact revert the mode of the instability and thus significantly change the spinodal patterns. Moreover, the maxima shift to small wavenumbers for increasing slip.