Static Light Scattering measurements on Microgels Below and Above Volume Phase Transition.

Polymeric microgels were synthesized from a polysaccharide at various crosslinker concentrations. Dynamic Light Scattering on these microgels revealed crosslinker-concentration-dependent dynamics below and above their volume phase transition. A proper multi-concentration Static Light Scattering (SLS) with direct dn/dc measurements, Zimm/Berry analysis, and form factor analysis was used to study particle’s structure, molecular weight, and interactions under various conditions.  While at low crosslinker concentrations microgel dn/dc was largely in agreement with the dn/dc value for the parent polymer, at high crosslinker dn/dc showed a significant increase with increase of crosslinker concentration and temperature. Microgel scattering form factors were also found to depend on crosslinker concentration changing from shapes consistent with more spherical to less spherical shapes with the increase of the crosslinker. The overall light scattering analysis shows that the crosslinker concentration affects the apparent density and structure of microgels and could be related to non-uniform crosslinker distribution in microgels at higher crosslinker concentrations. The argument for a future higher resolution probing of microgel internal structure with small angle scattering methods will also be made.