Effects of Low-Energy End Groups on the Dewetting Dynamics of Poly(styrene) Films on Poly(methyl methacrylate) Substrates

The influence of surface-active fluorocarbon-terminated poly(styrene) (PS−F) additives on the dewetting dynamics of thin melt films of poly(styrene) (PS) deposited onto poly(methyl methacrylate) (PMMA) substrates is investigated by reflection optical microscopy. The dewetting velocity is found to be time invariant and decreases with increase in PS−F content. Dewetting is completely eliminated for the neat PS−F films. The surface tension reduction due to PS−F addition is characterized by analysis of water contact angles on the PS blends and by measurement of equilibrium contact angles for droplets of the dewetted blends on PMMA by atomic force microscopy. Increasing the PS−F content decreases the PS blend surface tension and reduces its equilibrium contact angle on PMMA. Lower molecular weight PS−F is more effective in reducing the dewetting velocity owing to its higher fluorocarbon content and subsequently larger reduction in surface tension. The dependence of dewetting velocity ( V ) on the PS blend viscosity (η), surface tension (γ), and contact angle on PMMA (θ E ) is in excellent agreement with the relationship V = γ(θ E ) 3 /(12 L η√2) proposed by Brochard-Wyart, Martin, and Redon (BMR). The value of the prefactor L is found to be 16.4 for both series of blends, similar in magnitude to previously reported values for poly(dimethylsiloxane).