Small-angle light scattering study of droplet break-up in emulsions and polymer blends

The potential of using small-angle light scattering (SALS) to probe morphological changes induced by flow in immiscible polymer blends is investigated. Well-defined flow histories are shown to result in SALS patterns that are characteristics for the morphology involved. The pertinent structural change caused by either suddenly applying flow or drastically increasing the shear rate is the stretching of inclusions into long filaments, which subsequently break up by Rayleigh instabilities. Scattering models are developed to calculate the SALS patterns resulting from a filament with a sinusoidally disturbed surface and from a series of aligned spheres. These models capture the main features of the measured SALS patterns and are used to extract quantitative morphological information of the system. This is demonstrated by comparing calculated and measured results for droplet and filament size. In this manner an in situ, time-resolved technique becomes available to follow flow-induced structural changes such as those occurring during processing of blends.