Phase behavior of complex coacervates

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Arun Yethiraj of the University of Wisconsin-Madison is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry and the Condensed Matter and Materials Theory program in the Division of Materials Research to study the phase behavior of complex coacervates. Polymers are long chain like molecules that are ubiquitous in applications, e.g., plastics, and in biology, e.g., DNA and proteins. Mixtures of positively and negatively charged polymers, called coacervates, can form "droplets" of a separate dense liquid phase. An example is micron-sized assemblies composed of RNA and proteins in living cells that are implicated in many biological processes. They might also play a role in the origin of life, because these droplets can form in the absence of lipids, and the nucleic acids could have promoted catalysis in the early universe. These mixtures are also of interest in materials science where they find applications in drug delivery agents, coatings, and adhesives. They are of fundamental interest because of their fascinating properties, and obtaining relationships between the chemistry, structure, and property is a challenging task. Professor Yethiraj and his group are studying the mechanism of this phase behavior using an array of theoretical and computational methods, with the aim of understanding the principles of this phase separation and how it might be controlled. His group is involved in coaching middle and high school science Olympiad teams, and involving them in modern computational methods.Professor Yethiraj and his group are working on two parallel approaches for the study of complex coacervates. In the first they are developing atomistic, fully polarizable force-fields from first-principles, and using these to bench-mark coarse-grained models. They are using these to study the conformational and structural properties using computer simulations. In the second they are developing and implementing molecular classical density functional theory which can be tested against simulations and then used to obtain the phase behavior. The outcome will be a set of efficient tools that can used to study any complex polymer solution and an understanding of the mechanism of coacervation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.