Electrophoretic Behavior of PolyA-graft-PolyB-Type Microcapsules

Poly(1,4-piperazine-alt-terephthalic acid)(polyPT) microcapsules on which poly(methacrylic acid)(polyMA) or poly(4-vinylpyridine)(polyVP) is grafted were prepared by combination of an interfacial polymerization technique and radical polymerization, and the electrophoretic mobility of the microcapsules prepared was measured as a function of the ionic strength of the medium at different pH values. PolyPT microcapsules showed negative mobility values even in the media of low pH values and low ionic strengths, indicating that the microcapsules have practically no positive charge. The mobility decreased in its absolute value as the ionic strength of the medium increased. The absolute value of the mobility of polyPT-graft-polyMA microcapsules was larger than that of polyPT microcapsules due to negative charges of the carboxylic acid groups on the grafted polyMA chains. An increase in the amount of polyMA grafted on polyPT microcapsules brought about an increase in the absolute value of electrophoretic mobility. PolyPT-graft-polyVP microcapsules were found to migrate toward the cathode in aqueous media of low pit values independent of medium ionic strength, while they exhibited slightly negative mobility values in the media of pH values higher than 5. The mobility decreased at low pH with increasing ionic strength of the medium, whereas it remained almost unchanged at any ionic strength when the pH of the medium was higher than 5. The mobility data thus obtained were analyzed with a membrane model in which the fixed charged groups are uniformly distributed in an ion-penetrable surface layer of finite thickness.