NONUNIFORM SWELLING OF ALKALI SWELLABLE MICROGELS

Static and dynamic light scattering were used to study changes in the internal polymer segment density and particle swelling during the alkalization of aqueous dispersions of internally cross-linked, acid-containing latices (microgels). Upon neutralization, the microgels swell in excess of 200 times by volume, as evidenced by the measured hydrodynamic radius, R(h). Pronounced negative deviations of the ratio of the radius of gyration, R(g), to R(h) from the known value for homogeneous spheres along with curvature in Guinier plots of the angular dependent light scattering intensity indicate a nonuniform polymer segment density distribution within the microgels. Utilizing a simplistic core-shell model, we have determined the influence of the degree of neutralization, microgel cross-link density, and ionic strength on the nonuniform microgel swelling.