Determination of the inhomogeneous deswelling of thermoresponsive poly(N-isopropyl methacrylamide) microgels by combining dynamic light scattering, high-speed atomic force microscopy, and electrophoresis

Abstract

Poly(N-isopropyl methacrylamide) microgels with a uniform size of approximately 250 nm in their swollen state were synthesized via aqueous free-radical precipitation polymerization. The electrodynamic phenomena of the microgels were analyzed quantitatively using Ohshima’s equation, which explains the electrodynamic phenomena of natural and artificial soft colloids. The thermoresponsive deswelling of the microgels with increasing temperature was investigated by combining electrophoresis with dynamic light scattering and high-speed atomic force microscopy. Based on the obtained results, a plausible mechanism for the structural change during microgel deswelling is proposed, in which the core dwells first and the outermost surface dwells last. The thermoresponsive behavior of the microgels, the surface properties, and the core region of the microgels were evaluated independently using light scattering, electrokinetic measurements, and high-speed atomic force microscopy. The heterogeneous deswelling behavior of the microgels was revealed by combining these techniques.