(383b) Compatibilizer Distributions On Drops Resulting From Flow Induced Deformation and Breakup

The blending of two inmiscible polymers is usually carried out in the presence of a compatibilizer, namely a copolymer made from oligomers of the two bulk phase polymers. This copolymer is surface active, and acts in a flow as a large surfactant that reduces interfacial tensión, and induces Marangoni effects during both breakup and coalescence of drops. One result of the added compatibilizer is that the average size of the disperse phase component in a blend is much smaller than it would be in the same process without compatibilizer. Another consequence of the compatibilizer is that it strengthens the interface between the disperse and continuous phases in the ultímate blended material. Especially for this latter role, it is desirable if the  concentration of copolymer on the drop interface is the same on every drop. In the present study, we show experimentally that the copolymer concentration after stretching and interfacial tensión driven breakup in an extensional flow is non-uniform. The surprising result from numerical simulation of the stretching and breakup process is that this nonuniformity comes primarily from the redistribution of the copolymer during the interfacial tensión driven relaxation and breakup process. Although the flow in the stretching process initially induces strong concentration gradients as the copolymer is swept toward the ends of the drop, once the drop is elongated sufficiently it begins to stretch approximately affinely and then the concentration distribution returns to an approximately uniform state. Hence, if the drop is stretched sufficiently to lead to breakup when the flow is turned off, the copolymer concentration distribution produced by the stretching process is nearly uniform.