Stabilization of dispersed domains in polymer blends by addition of low molecular weight diblock copolymer

About 5 wt% of low molecular weight poly(isoprene-block-dimethylsiloxane) was added into a poly-isoprene/polydimethylsiloxane 3:7 blend and a polydimethylsiloxane/polyisobutylene 3:7 blend and tested as a surfactant. Samples were sheared at a constant shear rate (16 sec^-1) by a rheometer using cone-plate geometry. Viscoelastic properties of blends with and without diblock copolymers (bcp) after the pre-shear measured by dynamic measurements were almost the same. After the pre-shear, small amounts of samples were carefully removed from the cone-plate and the variation of domain size was observed by a microscope. After several hours, the domain size of blends without bcp became 4 to 6 times as large as that observed after the cessation of pre-shear, while that of blends with bcp was stable for a long time. Under the successive shear flow with lower shear rate than the pre-shear, it was observed that the dispersed domains of polyisoprene/polydimethylsiloxane/bcp system first coalesced till the size became twice as large as the original size. Then the domains became stable for a long time.