(619g) Ion and Cooperativity Effects in Complex Coacervate Structure

Authors: 
Sing, C., University of Illinois Urbana-Champaign
Perry, S. L., UMass Amherst
Tirrell, M., University of Chicago
Olvera de la Cruz, M., Northwestern University

Complex coacervates are solutions of oppositely-charged polyelectrolytes that can undergo liquid-liquid phase separation to form polymer-rich and polymer-deficient phases. The physics governing this system is relevant to a whole host of biopolymeric and synthetic systems with applications ranging from drug encapsulation to layer-by-layer assembly. Widely-used Voorn-Overbeek theory is often used to explain the coacervation process, and is typically reasonable in many of its predictions. Nevertheless, it is based upon classical Debye-Huckel theory that is known to be insufficient in the conditions realized in typical coacervation experiments. We instead use the Polymer Reference Interaction Site Model (PRISM), which is an extension of Liquid State theory ideas, to gain insight into the local organization of chains and ions such that we can elucidate the physical driving forces in complex coacervation. We demonstrate a rich array of behaviors such as cooperative interactions between the polyelectrolytes, finite salt size effects, the effects of valency, and discuss how Voorn-Overbeek based models tend to provide reasonable experimental estimates despite being based on incorrect assumptions. We show how these results relate to experimental data suggesting the presence of ion-specific effects, and correspondingly demonstrate an expanded set of parameters in which complex coacervates may be tuned by the design of both the polymer and salt components.

C.E.S. acknowledge support from the International Institute for Nanotechnology, S.L.P. and M.T. acknowledge support from the U.S. Department of Energy Office of Science program in Basic Energy Sciences and the Material Sciences and Engineering Division.