Studying the Volume Phase Transition of Polymeric Microgels

This project investigated volume phase transition of polysaccharide microgels synthesized in a surfactant solution. The addition of surfactant raises the Lower Critical Solution Temperature (LCST) of the polymer. Maintaining LCST for 3 hours is crucial for microgel synthesis. Three baths were used to achieve these stable synthesis conditions. While most microgels were synthesized in +/-0.1C bath, microgels synthesized in a less stable baths were found to have larger hydrodynamic radii (R_h). The synthesis conditions were varied systematically by changing amount of used cross-linker and surfactant. The resulting microgels were characterized using Dynamic Light Scattering (DLS) at multiple angles and temperatures varying from 20 to 60C. Flory-Huggins Mean Field theory was used to describe microgel’s deswelling with increase of temperature. The theoretical model was fit to the experimental DLS data. Fit results, including enthalpy, entropy, number of polymer chains per microgel, and a material constant, suggest a dependence of polymer chain interactions during synthesis on the amount of cross-linker. Further development of the Flory-Huggins model is needed to fully account for effect of cross-linker and surfactant on synthesized microgels.