ARTICLE pubs.acs.org/Macromolecules
Growth of Noncircular and Faceted Holes in LiquidLiquid Dewetting of Thin Polymer Bilayers Lin Xu,† Ashutosh Sharma,*,†,‡ and Sang W. Joo*,† † ‡
School of Mechanical Engineering, Yeungnam University, Gyongsan 712-749, South Korea Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, India ABSTRACT: Although the formation of circular holes is the norm in the spontaneous dewetting of thin polymer films, we show highly anisotropic hole growth leading to irregular and faceted shapes in dewetting of the upper polystyrene layer in a thin polymer bilayer (silicaPMMAPSair). The irregular shapes are formed when viscous dissipation is dominated by the upper PS dewetting layer under the conditions of its much higher viscosity and lower thickness or the lower viscosity and higher thickness of the substrate PMMA layer. These conditions engender strong slippage of the dewetting layer, resulting in very broad rims and the long-range viscous interactions among randomly distributed, initially circular holes. The growth occurs selectively in the directions of less viscous resistance. Thus, the irregular growth of holes can be inhibited by increasing the PS film thickness or by decreasing the PMMA film thickness.
’ INTRODUCTION Thin polymer films are found in a host of modern technologies from coating, painting, lithographies, self-organized patterning, diffusion, to multilayer adsorption, etc. Instability of thin polymer films on a solid substrate is thus an important phenomenon. The usual scenario for the initial stages of dewetting of a thin (
