(606d) Locally Glassy Dynamics in Colloidal Systems with Competing Interactions
Colloidal systems with a combination of short-range attraction (SA) and long-range repulsion (LR) have received significant interest due to their wide variety of solution states. Of these, cluster fluids and kinetically trapped states reminiscent of purely SA systems have received particular attention. In particular, these states have been observed in concentrated formulations of monoclonal antibodies, a powerful and prevalent oncology therapeutic. While dynamic arrest at intermediate volume fractions (i.e., gelation) driven purely by attraction has been heavily studied (and remains under debate), the influence of an additional repulsive force is poorly understood. To study these systems, we use highly purified lysozyme, which is well-known to interact via an SALR potential at low ionic strengths. Over a broad range of protein concentrations, the solution structure is quantified using small angle neutron scattering while the dynamics over short times is directly measured using neutron spin echo and over long times is inferred from viscosity measurements. While the viscosity displays Newtonian behavior under all conditions, the short time dynamics become sub-diffusive at elevated protein concentrations and low temperature. This disparity in short and long time dynamics is correlated with the formation of intermediate range order, but only occurs at concentrations well beyond the structural percolation transition. These heterogeneous percolated networks contain localized regions of high density that reduce protein motion, resulting in glassy-like behavior over short times, yet maintain macroscopic liquid-like behavior. The structural and dynamic characteristics of SALR systems found here are distinct from macroscopically heterogeneous attractive driven gels, but may provide insight into the mechanism of kinetic arrest in those systems.