Studies on microcapsules

Abstract

Potentiometric titrations and electrophoretic mobility measurements were made on carboxylated polyphthalamide microcapsules prepared by the interfacial polycondensation method. The values of surface potential and zeta potential of the microcapsules were calculated by using a theoretical potentiometric equation and the simple Smoluchowski equation, respectively. The ionic strength of the medium was found to have no effect on the conformation of the polymer chains of the microcapsules. The negative surface potential obtained from potentiometric titration data rose first with increasing pH of the medium and then tended to level off as the pH approached 7 while the zeta potential as evaluated from electrophoresis data was found to change until the pH attained a value of 10. The cause for this difference in pH change between the surface potential and the zeta potential of the microcapsules was ascribed to the reason that potentiometric titration does not permit the detection of terminal amino groups of the polymer chains constituting the microcapsules, which are far smaller in number than the carboxyl groups, while electrophoresis can detect the presence of the terminal amino groups.