(495a) Preparation And Rheology Of Double Emulsion Morphologies In Compatibilized Immiscible Polymer Blends

Block copolymers, termed compatibilizers, are often added to immiscible polymer blends to improve blending. It is well known that a compatibilizer improves blending through a combination of a decreased interfacial tension and the ability to suppress droplet coalescence. The aim of this research is to exploit the ability of the compatibilizer to suppress coalescence to create unusual morphologies in immiscible polymer blends. Drop-in-drop morphologies (double emulsions) were created using specific mixing protocols on blends of poly(dimethyl siloxane) (PDMS) and polyisobutylene (PIB) compatibilized by a small amount of a PIB-PDMS diblock copolymer. Previous work has shown that for this system coalescence is suppressed by the compatibilizer only if PIB is the continuous phase.

We used a stress-controlled rheometer to study the steady shear viscosity, creep recovery after cessation of shear, and dynamic oscillatory behavior of the double emulsion blends, along with their simple emulsion counterparts containing the same component volume fractions. Previous results on simple emulsions show that the blend viscosity and recovery increase slightly with small amounts (less than 1%) of compatibilizer. Both of these results are seen here, but additional increases in viscosity and recovery are seen in the double emulsion blends, and are attributed to the higher effective volume fraction of the double emulsion drops. Through the use of an emulsion model, we show that the double emulsion blends may behave rheologically like simple blends with an increased effective volume fraction and a drop phase that has the properties of a blend itself.

Furthermore, we found that under high-stress, rapid mixing, the double emulsion sub-drops were able to ?leak? from the outer drops and coalesce with the matrix. We were able to use rheology, along with fluorescence microscopy, to probe the effectiveness of double emulsion formation, i.e. if a double emulsion is formed and if major sub-drop leakage occurred.