Shear-induced coalescence in aqueous biopolymer mixtures

This work is focused on the investigation of coalescence under shear flow in aqueous mixtures of Na-alginate and Na-caseinate. Shear flow was generated in a parallel plate apparatus coupled with an optical microscope. Drop size distribution was measured as a function of time by computer controlled 3D optical sectioning of the sample and offline image analysis. Automated procedures of image analysis, based on out-of-focus components subtraction and drop contour detection, were implemented to measure a large number of drops, as required to minimize sampling errors. The effects of dispersed phase volume fraction and shear rate on the flow-induced evolution of the drop size distribution were explored. Finally, 3D reconstruction of the locations of the drops within the sample was performed to evaluate possible wall and sedimentation effects.