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

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.