Influence of block copolymer on droplet breakup and coalescence in model immiscible polymer blends

Shear-induced droplet breakup and coalescence were investigated by optical microscopy. Model polymer blends comprising 5% poly(propylene oxide) (PPO) dispersed in a poly(ethylene oxide) (PEO) matrix were studied in situ. Addi tion of 0.1% or 1.0% of PEO-b-PPO-B-PEO triblock copolymers facilitated bre akup and inhibited coalescence. The steady-state,droplet size produced by b reakup was reduced only slightly by addition of 0.1% copolymer and more sub stantially by addition of 1%. However, the kinetics of coalescence were sup pressed effectively even when 0.1% of copolymer was added, and only margina l additional gains in suppressing coalescence were achieved by addition of more copolymer. Analysis of coalescence kinetics shows that in these system s the copolymer acts to reduce the efficiency of both droplet collision and film drainage and/or rupture.