The wettability of ultrathin polymer films (< 100 nm thick) is a critical processing parameter in nanolithography, flexible electronics, and coatings; however, the reduced thickness effects (i.e., nanoconfinement) remain underexplored even though wettability is a macroscopic manifestation of molecular-level intermolecular forces, such as van der Waals (vdW) interactions. The previous works primarily have focused on utilizing vdW interaction to describe the ultrathin film stability without considering the potential impacts of nanoconfinement. To this end, we investigate the role of nanoconfinement effects on vdW interactions in governing the stability of multilayer ultrathin polymer films via a comprehensive analysis of dewetting behaviors of trilayer polymer thin films. The trilayer polymer stack comprises a 450 nm bulk polystyrene (PS) bottom layer, a poly(methyl methacrylate) (PMMA) middle layer of variable thickness (15–95 nm), and a 10 nm PS top layer that undergoes dewetting to serve as a probe for evaluating the intermolecular forces across the system. While we confirm previous findings that the stability of the top PS film depends strongly on the thickness of the PMMA layer, vdW predictions from conventional theoretical models, based on Lifshitz theory and Hamaker constants derived from bulk material properties, fail in the thin PMMA regime. We addressed this discrepancy by accounting for refractive index changes with decreasing film thickness due to nanoconfinement. With this refinement, our model accurately predicts the observed dewetting behavior across the full range of PMMA thicknesses. These findings highlight that nanoconfinement can significantly influence vdW interactions and, consequently, thin film stability. Our work underscores the importance of moving beyond bulk assumptions in modeling ultrathin polymer systems and provides a framework for tuning the stability of multilayer polymer interfaces in advanced material applications.
