Dewetting of a pre-patterned thin polymer bilayer: influence of the instability mode

Abstract

In this paper, the influence of film thickness on the layer instability mode of a thin polymer bilayer (poly(methylmethacrylate) (PMMA)/polystyrene (PS)/Si substrate) has been investigated. The experimental results show that kinetic forces can greatly influence the instability process of the thin polymer bilayer. In the case of PS-2.4K (M_w-PS = 2.4 kg mol⁻¹), only the PS layer ruptures between the PMMA layer and the solid substrate and the dewetting is kinetically controlled. In the case of PS-31K (M_w-PS = 31 kg mol⁻¹), the instability of the polymer bilayer changes from a kinetically controlled one to a thermodynamically controlled one with the increase of PS film thickness. In the case of PS-97K (M_w-PS = 97 kg mol⁻¹), only the PMMA layer ruptures on the PS layer and the dewetting process is a thermodynamically controlled one. Besides, the influence of the instability mode on the template-assisted dewetting process of the thin polymer bilayer also was studied. After annealing the pre-patterned bilayer, in the case of the kinetically controlled dewetting, the PMMA film bends to conform to the buried PS–PMMA interface and concave half cylinder grooves form during the dewetting process; however, in the case of the thermodynamically controlled dewetting, PMMA chains move to the top of cylinder stripes and obvious trenches are found after PMMA chains are etched. This proposes a simple method to obtain different surface structures by changing the instability mode of the thin polymer bilayer.