The effects of viscosity on coalescence-induced coalescence

The effects of variable matrix-phase viscosity on the rate of coarsening of relatively inviscid diluent droplets in a viscous polymer matrix are examined. Emulsions of low viscosity diphenyl ether (DPE) droplets in a viscous matrix mixture of isotactic polypropylene (iPP) and DPE are formed by thermal quenching of a homogeneous phase below the binodal. The droplets coarsen via the mechanism of coalescence-induced coalescence (CIC), where two coalescing droplets create a flow that drives other droplets to coalesce, thus creating a cascade process. Previous work on CIC indicate that the growth exponent of the average droplet size depends on the volume fraction of the diluent phase, but does not depend on the viscosity of the matrix phase or the DPE–iPP interfacial tension. Different iPP molecular weights in the experiments cause a variation in the viscosity, but practically no change in the interfacial tension nor in the phase behavior of the system. The growth exponent is found to not vary with the viscosity of the matrix phase, supporting the CIC theory.