Taming Anomalous Dewetting Dynamics in Enthalpically Inverted Polymer Bilayers

The dewetting dynamics of an enthalpically inverted immiscible poly-2-vinylpyridine (P2VP) and polystyrene (PS) bilayer thin film on a solid substrate were investigated. Our findings reveal that the metastable layer undergoes dewetting through nucleation and growth, with the time evolution of dewetting holes being strongly influenced by the viscosity contrast between the layers, which depends on the molecular weight of each polymer. Notably, our observations deviate from theoretical predictions of liquid–liquid dewetting in two key ways: (i) Accelerated dewetting dynamics were observed in high/ultrahigh molecular weight polymer pairs with similar viscosities. (ii) Significant interfacial deformation occurred in bilayers with low viscosity (comparable to the entanglement molecular weight) and viscous dissipation in the bottom layer. Focusing on these two findings, we quantified a spring constant associated with the restoring force that governs the film’s ability to accelerate hole-opening events and deform the less viscous bottom PS layer by the highly viscous top P2VP layer, which indents into it. This behavior reflects the competition between dewetting, driven by unfavorable intermolecular interactions at the P2VP-PS interface, and partial layer inversion due to the lower surface energy of PS and the favorable interaction of P2VP with the Si substrate. We further explained how the dynamics of the instability and the topography of prominent patterns─such as the internal flat rim formed in the low-viscosity bottom PS layer─are influenced by the differing molecular mobilities of the two layers, depending on their relative viscosity contrast and competitive interactions with the solid Si substrate.