(338q) Departures from Expected Diffusive Behavior in Concentrated Associating Polymer Solutions Uncovered Using Single Particle Tracking

Associating polymer system dynamics are governed by non-covalent interactions such as hydrophobicity and dipole interactions that cause them to self-assemble and exhibit long-range ordering and aid in applications such as contaminant removal and drug delivery. The diffusion of the associating polymer species is central to the effectiveness of these applications. This diffusion is environmentally dependent, deviates from the behavior of neutral polymers, and can be fine tuned through synthetic or environmental means to achieve the desired application. We use single particle tracking (SPT) to determine the diffusive behavior of a hydrophobically associating polymer, poly(poly(ethylene glycol) methacrylate) (pPEGMA), and a polyelectrolyte, polylysine (PL). Because of hydrophobic interactions, pPEGMA chains may exist in solution as unimers or form clusters. Aided by the single-molecule resolution of SPT, we observe the mean square displacements of polymer chains in solution show a clear two-population division, with each population individually analyzable. This trend is easily recognizable in the distributions of final polymer displacements and the Van Hove distributions determined from the SPT data as well. This clustering behavior is readily tunable with polymer concentration, degree of polymerization, and solvent polarity. Notably, when combined with ¹H NMR diffusion-ordered spectroscopy, scaling relationships for the diffusive regimes up to semidilute entangled regime are recovered from the average diffusion coefficients at each polymer concentration. We also use SPT to study polymer diffusion in concentrated solutions of PL, which relies on the electrostatic interactions between adjacent chains as well as the physical interactions between chains. These experiments illustrate the effect of these electrostatic interactions, as an exceptionally strong polymer concentration dependence is seen for diffusivity. A stronger than expected trend is in concentrated systems with various counterion concentrations ranging from ion-exchanged, low concentration samples to samples approaching the solubility limit for salt. The leading explanations for this strong dependence are rooted in an increase in frictional resistance due to overlapping electrostatic blobs in the system and an increased prevalence in polymer-polymer interactions in the system compared to theoretical predictions describing less concentrated systems.