Migration of nanosilica particles in polymer blends

Hydrophilic pyrogenic silica melt mixed in immiscible polypropylene/poly (ethylene-co-vinyl acetate) (PP/EVA) blend was found to migrate from the PP matrix to the EVA dispersed domains and remained confined inside them. Surprisingly, it was shown than silica was also able to migrate from a dispersed PP phase to an EVA matrix but this transfer was slower and not complete. The same silica with a hydrophobic surface treatment moved and accumulated to the blend interface and in PP. The mechanisms from which this migration proceeds are discussed. Whereas self diffusion of the particles was shown to have almost no effect, shear induced movements and collisions with dispersed drops is believed to be the most efficient mechanism. The possible trapping of silica aggregates during droplet-droplet coalescence was impossible to observe but is thought to be a possible additional mechanism. No quantification on the relative importance of the latter phenomenon can be drawn at the moment.