Morphology development during phase inversion in isothermal, model experiments: steady simple-shear and quiescent flow fields

Abstract

The effect of component viscosities on phase inversion was examined under two idealized flow fields: steady simple-shear and quiescent. In both cases, disk samples with a specific initial morphology — major-component pellets in a minor-component matrix — were prepared. For the steady simple-shear flow experiments, the evolution of morphology with strain was determined. The same stages of morphology development were observed in all blends; however, the rate of morphology development decreased with increasing effective viscosity ratio. The quiescent experiments tested whether phase inversion occurred in samples that were annealed for a set time. Blends with lower absolute viscosities phase inverted faster. Lattice-Boltzmann simulations demonstrated a functional dependence of t c ∗∝Z −0.36λ 0 −0.73 based on the dimensionless time to phase inversion t c ∗, Ohnesorge number Z, and viscosity ratio λ 0. This dependence, when extrapolated to the experimental processing window, agrees with the experimental results and indicates that the dimensional time to phase inversion under quiescent conditions depends on η minor 0.37 η major 0.27. Data from both flow fields indicate that phase inversion occurs when the minor component reaches a critical film thickness. This thickness under steady, simple-shear flow was 0.2–0.3 μm at low strain rates. The results from the two flow fields differ in the driving force behind film thinning: shear deformation of the major component drives film thinning under steady, simple-shear flow; interfacial-tension drives it under quiescent conditions.