Surface properties of monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres prepared by a membrane emulsification technique

Abstract

Monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres of different average sizes were prepared using a membrane emulsification technique. The average diameters of the microspheres were dependent on the pore sizes (0.33, 0.73, 1.15, and 1.70 μm) of SPG membranes used in the preparation procedure. The surface properties of microspheres have been studied from their electrophoretic mobility values. The mobility values of poly(acrylamide- co-acrylic acid) microspheres were negative at pH 7.4 with ionic strengths between 0.005 and 0.154 at 25°C. More negative mobility values were obtained with smaller poly (acrylamide- co-acrylic acid) microspheres than with the larger ones. By analyzing the data with an electrokinetic theory for `soft' surfaces, it was found that copolymerization of acrylamide monomers and acrylic acid monomers does not proceed homogeneously within a microsphere. The density of polymer networks composed of both monomers is higher in the core region than in the surface layer of the microspheres. This is not the case for smaller microspheres, hence their electrophoretic mobility becomes more negative.