Coacervation of ethyl cellulose: The role of polyisobutylene and the effect of its concentration

The influence of polyisobutylene (PIB) on the phase separation of ethyl cellulose (EC) from cyclohexane by temperature reduction was studied by measurement of the phase coacervation volume (PCV) and particle size and by SEM examination of the coacervate obtained. PIB concentration effects on phase properties were delineated by means of a phase diagram. In the absence of PIB or at low concentrations, EC aggregates were formed whereas higher concentrations yielded stabilized droplets. Microanalysis indicated that PIB was not coprecipitated and hence functions as a stabilizer by adsorption. Increased PIB concentration raised the PCV and decreased the particle size in nonlinear dependence. The PCV change resulted from Stokes law sedimentation kinetic effects. MW increase of PIB at constant solution viscosity increased the PCV and decreased the particle size, indicative of increased stabilization. There was a negative linear dependence of diameter on medium viscosity. It was concluded that increase of viscosity and protective colloid concentration modulated the rates of the EC separation, growth, and aggregation processes and led to stabilization of droplets at an earlier stage of growth and suppression of regular surface nucleation and crystallization of the polymer.