(207c) Diffusion and Nanoscale Structure in Polyelectrolyte-Colloid Coacervates by Pulsed Field Gradient NMR

Colloidal systems consisting of oppositely charged polyelectrolytes and small colloids often exhibit liquid-liquid phase separation. The phase with a higher density and higher colloid concentration is known as the coacervate. Protein-polyelectrolyte coacervates show some interesting transport and rheological properties, which make them good candidates for applications such as drug encapsulation and enzyme immobilzation. The properties of coacervates are determined by their structure, which is believed to be inhomogeneous over a broad range of length scales; however, previous studies focused on the dynamics and structural arrangement of only the protein component. In this work, the diffusion of the polyelectrolyte was studied using a new approach, i.e. pulsed field gradient (PFG) NMR with high (up to 30 T/m) magnetic filed gradients. Diffusion measurements were carried out for a broad range of diffusion times corresponding to displacements of polyelectrolyte around 100 nm and larger. The experimental data provide evidence for the existence of domains with sizes smaller than around 1 micron. These domains are characterized by high polyelectrolyte diffusivity. These results are in a qualitative agreement with the data obtained previously using Cryo-TEM, rheology, FRAP, FCS, DLS and neutron scattering.