Diblock copolymers and steric stabilization during flow

A hypothesis (theory) has been formulated for steric stabilization during simple shear flow of discrete domains of one polymer A in a continuous phase B by block copolymer addition. A limiting solution found when the molecular weights of the components are high predicts preformed small drops stabilized by block copolymers at the interfaces are stable below a critical shear stress τ cr but unstable above τ cr Interfacial placement in well dispersed blends of PS/PMMA/PS-b-PMMA was deduced by interfacial tension measurement, structure development studies, and viscosityshear rate studies with and without block copolymers. The experimentally determined critical shear stresses show relatively poor reproducibility (SD ± 10%). For measurements at shear stresses larger than the critical values, interesting time effects are observed, whereas scattering signals are constant at shear rates lower than τ cr The hypothesis is not rejected when compared with experimental data from light-scattering measurements during flow.