Shear stability of polymeric colloidal dispersions : interplay between aggregation and coalescence

The aim of the present work is to study the role that coalescence plays in the aggregation under shear of polymeric colloidal dispersions. Understanding the role of coalescence is very important not only from the scientific point of view, since at the moment in the literature a unified depiction of this phenomenon is missing, but also from the industrial one: indeed, coalescence is involved in many applications concerning the manufacture of polymer colloidal products and the design of polymer processes. In the present study four samples of poly(methyl methacrylate –co- butyl acrylate) latexes have been synthesized by starved emulsion polymerization in a semi-batch reactor. Changing the monomer ratios leads to polymer particles exhibiting a glass transition temperature gradient which allows studying the coalescence process. The coalescence behavior of our systems has been first clarified in stagnant conditions; while in a second stage shear conditions have been investigated.