Preparation and Characterization of Temperature Sensitive Poly (N-Isopropylacrylamide) Microgel Latexes

Abstract

<p> Temperature sensitive microgel latexes of poly (N-isopropylacrylamide) cross-linked with N-N'methylene bisacrylamide (BA) were prepared and characterized by Dynamic Light Scattering, Titration and Electrophoresis. The study of gels, including temperature sensitive gels, is limited by the large size of traditional bulk gels which are slow to respond to changes and are difficult to measure. An alternative system, which may be easier to study, is a microgel latex which would constitute small particles of gel which would respond quickly to changes in their environment and could also be measured using colloidal measuring techniques like dynamic light scattering and particle electrophoresis.</p> <p> Monodisperse and stable microgel latex particles were prepared by reacting Nisopropylacrylamide (NIPAM) monomer with a cross-linking agent BA in water at 70°C with a surfactant (sodium dodecylsulfate) present. Latexes prepared without surfactant were polydisperse.</p> <p> Characterization of the poly (NIPAM) particles by dynamic light scattering at several different temperatures showed that the particles go through a transition from a water swollen gel at low temperature to a shrunken gel with a low water content at high temperature. The transition occurs about 32°C. The degree of swelling of the poly (NIPAM) particles can be expressed by the Flory-Huggins Interaction parameter c and is dependent upon the level of cross-linking agent included.</p> <p> Titration and electrophoresis results indicate that the particles contain about 0.39 Coulombs per gram of polymer of carboxylic and sulfuric charged end groups which are distributed throughout the particle.</p>