Influence of selective filling on rheological properties and phase inversion of two-phase polymer blends

We investigate the phase inversion of selectively filled polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends prepared by melt mixing. As we have shown by transmission electron microscopy analysis and by the calculation of different selectivity criteria, the filler used (glass spheres of submicron dimensions) resides exclusively in the PMMA-phase and modifies its rheological properties correspondingly. Four blend series made of PS and PMMA with different filler content are analyzed for the location of phase inversion concentration, phi(PI), and the width of the cocontinuity interval, CCI, in the concentration range where cocontinuity is predominant. Upon addition of filler a shift of 4, to higher concentrations of the filled PMMA-phase has been observed. This shift is in agreement with the predictions of a recently proposed equation defining the phase inversion concentration as that concentration where the maximum of the blends' extra elasticity occurs. The qualitative morphological analysis of these blends confirms this result. Moreover, it was found that the cocontinuity interval is widened significantly at increased filler content. We explain the appearance of a wider CCI for filled blends on the basis of a slowdown of processes leading to morphology destruction. Corresponding Tomotika experiments (stability of fibrils) substantiate these findings. (C) 2002 Elsevier Science Ltd. All rights reserved.