Shear-induced droplet coalescence in immiscible polymer blends and the effect of interfacial modification

The size and spatial distributions of droplets in immiscible fluid mixtures following well-specified shear histories were investigated by in situ microscopy. Mixtures of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) with and without additional triblock copolymer have been explored. At steady state, the experimental and theoretical concentration profiles represent a balance of shear-induced diffusion and wall migration towards the center of the cell. After a sudden reduction in shear rate, shear-induced coalescence occurs and its efficiency was measured directly and compared with recent numerical predictions by Rother and Davis. The ability of small amounts of copolymer to inhibit coalescence was found to correlate with copolymer interfacial pressure, obtained from interfacial tension measurements. The authors gratefully acknowledge the financial support of NSF grant CTS-9731502.