DIBLOCK COPOLYMERS AND STERIC STABILIZATION DURING FLOW

A hypothesis (theory) has been formulated for steric stabilization dur ing simple shear flow of discrete domains of one polymer A in a contin uous phase B by block copolymer addition. A limiting solution found wh en the molecular weights of the components are high predicts preformed small drops stabilized by block copolymers at the interfaces are stab le below a critical shear stress tau(cr) but unstable above tau(cr). I nterfacial placement in well-dispersed blends of PS/PMMA/PS-b-PMMA was deduced by interfacial tension measurement, structure development stu dies, and viscosity-shear rate studies with and without block copolyme rs. The experimentally determined critical shear stresses show relativ ely poor reproducibility (SD +/- 10%). For measurements at shear stres ses larger than the critical values, interesting time effects are obse rved, whereas scattering signals are constant at shear rates lower tha n tau(cr). The hypothesis is not rejected when compared with experimen tal data from light-scattering measurements during flow.