A Study of the Effect of Electrolyte on the Swelling and Stability of Poly(N-isopropylacrylamide) Microgel Dispersions

Abstract

Poly(N-isopropylacrylamide) (poly(NIPAM)) microgel dispersion stability has been investigated in the presence of a range of electrolytes. The stability of the dispersions to flocculation is strongly related to the free energy change of formation in aqueous solution for the anions (ΔGfo) and their position in the lyotropic series. The ability of the anions to induce particle deswelling and flocculation has been investigated using photon correlation spectroscopy and turbidity-wavelength measurements, respectively. Anions with a high charge density (and high negative values for ΔGfo) have the ability to dehydrate the poly(NIPAM) chain and induce flocculation. The ability of cations to induce particle deswelling and flocculation was also investigated. The ability of the cations to induce particle deswelling did not coincide with their values for ΔGfo and their position in the lyotropic series. Time-dependent turbidity measurements of collapsed particles in the presence of NaCl were used to calculate the Hamak...