Relating Dewetting and Molecular Forces of Sandwiched Ultrathin Polymer Films

Previous research has demonstrated that wettability and surface tension of polymer films often possess thickness dependence originating from underlayer effects and material property changes due to nanoconfinement. However, critical thicknesses at which the wetting behavior deviates from the bulk values are reported to be ~ 100 nm, which is an order of magnitude larger than van der Waals potential’s prediction. To investigate this discrepancy, we develop a tri-layered system consisting of a bottom layer of bulk polystyrene (PS, 450 nm thick), a middle of polymethyl methacrylate (PMMA, 15~150 nm thick), and a dewetting PS (20 nm thick) top layer. This system allowed us to investigate the evolution of the spinodal dewetting PS layer pattern over time as a function of PMMA middle layer thickness. Our results reveal that the spinodal pattern is influenced not only by the annealing time but also by the thickness of the middle PMMA layer, suggesting that molecular interactions can propagate the distance comparable to the middle layer’s thickness. We will further discuss the physical parameters, such as Hamaker constant, derived from Fourier transform of obtained images. This study presents an opportunity to modulate the surface wettability of polymer thin films without altering the surface chemistry, simply by the underlayer.