RHEOOPTICAL INVESTIGATION OF IMMISCIBLE POLYMER BLENDS

Linear conservative dichroism has been investigated as a potential too l for tracking tin situ and in real time) the flow-induced microstruct ure of immiscible polymer blends. Dilute mixtures of poly(dimethylsilo xane) in poly(isobutene) and vice versa have been used as model system s. It is demonstrated that different mechanisms for structural changes can be identified with this technique: droplet deformation, droplet r etraction, fibril break-up and coalescence. Time-resolved in-situ SALS measurements support the structural interpretation of the dichroism d ata. Breaking up of stretched filaments by Rayleigh instabilities can be deduced from dichroism measurements. The resulting strings of dropl ets can be detected with SALS. The time scales for the structural chan ges can be determined by dichroism, which makes it possible to study i n situ the effect of the various process and material parameters. As a n illustration, the effect of shear rate on fibril break-up and on dro plet coalescence after sudden changes in shear rate has been considere d. Break-up times decreased only slightly with increasing shear rate; coalescence times scaled with the square of shear rate rather than wit h strain under the conditions of the present experiments. (C) 1998 Els evier Science Ltd. All rights reserved.