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

The effect of component viscosities on phase inversion was examined under t wo idealized Row fields: steady simple-shear and quiescent. In both cases, disk samples with a specific initial morphology - major-component pellets i n a minor-component matrix - were prepared. For the steady simple-shear Row experiments, the evolution of morphology with strain was determined. The s ame stages of morphology development were observed in all blends; however, the rate of morphology development decreased with increasing effective visc osity ratio. The quiescent experiments tested whether phase inversion occur red in samples that were annealed for a set time. Blends with lower absolut e viscosities phase inverted faster. Lattice-Boltzmann simulations demonstr ated a functional dependence of t*(c) proportional to Z(-0.36)lambda (-0.73 )(0) based on the dimensionless time to phase inversion ta, Ohnesorge numbe r Z, and viscosity ratio lambda (0). This dependence, when extrapolated to the experimental processing window, agrees with the experimental results an d indicates that the dimensional time to phase inversion under quiescent co nditions depends on eta (0.37)(minor) eta (0.27)(major). Data from both flo w fields indicate that phase inversion occurs when the minor component reac hes a critical film thickness. This thickness under steady, simple-shear ho w was 0.2-0.3 mum 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 Row; inter facial-tension drives it under quiescent conditions. 2001 Published by Else vier Science Ltd.