FLOW INSTABILITIES IN POLYMER BLENDS UNDER SHEAR

The effect of shear flow on the miscibility behaviour of the model pol ymer blend polystyrene/poly(vinyl methyl ether) has been investigated in real time by two-dimensional light scattering and optical microscop y. Under certain shear and dynamic temperature conditions large 'waves ' have been observed which are aligned either in the direction paralle l to the applied shear flow or just off it. Two-dimensional light scat tering patterns from samples under the same conditions show sharp stre aks aligned in the direction perpendicular to the flow. The evidence p resented in this work indicates that these 'waves' are unlikely to be elongated phase-separated domains; instead, they could be caused by fl uid instabilities.