Using Static Light Scattering (SLS) to Determine the Structure of Polymeric Microgels

We synthesized polysaccharide microgels with varying crosslinker concentrations, resulting in particles with different temperature dependent structure and dynamics depending on the crosslinker concentration. At least three behavioral regimes were observed in the microgel volume phase transition. It was found that with the increase of solution temperature microgels deswelled at low crosslinker, grew in size at high crosslinker, and showed a transitional behavior at intermediate crosslinker concentration. We studied structure of the microgels in each behavioral regime through SLS. The SLS data was analyzed using Zimm and Berry plots both above and below the volume phase transition yielding molecular weight, radius of gyration, and second virial coefficient. The SLS form factors were obtained and analyzed (e.g. using Kratky plots) both below and above the transition. Apparent and contrasting changes in the form factors were observed in different regimes during the transition. The applicability of common form factor models to the microgels in different regimes was considered. The measured form factors were also fit with various models (including hard and fuzzy sphere) by varying size parameters to determine analytically best structure describing the microgel SLS data.