(4eg) Statistical Physics of Ionic Polymer Systems for Rational Materials Design

The efficient design of polymer-based materials is strongly facilitated by predictive capabilities provided by theoretical and computational methods of polymer physics. Using my background in analytical theory and computer simulations of ion-containing polymers, I explore the relationship between the polymer structure and the resulting physical properties of the materials. In addition to the application-oriented activity, my research also deals with fundamental problems of polymer physics, including their biological context. The area of my scientific interests includes polymer (micro)gels, solutions, and micelles, complexes between oppositely charged polyelectrolytes, and polyampholytes.

My research group will apply approaches of polymer physics to study fundamental and applied problems that lie at the intersection of engineering, physics, chemistry, and biology. Combining analytical theory and computer simulations, I am going to explore the following directions:

(i) Liquid-to-Solid Transitions in Polyelectrolyte Complexes

Solutions of oppositely charged polyelectrolytes undergo macroscopic phase separation into dilute supernatant and polymer-rich phase. Depending on the polymer chemistry and external conditions such as temperature and salt concentration, this polymer-rich phase can be either liquid (usually called polyelectrolyte complex coacervate) or solid. The rheological properties of these two states are drastically distinct, their storage and loss moduli differ by many orders of magnitude. However, microscopic understanding of these (presumably glass-like) transitions is very limited. I plan to use theory and coarse-grained simulations to provide deep physical insight into this problem. Since macroscopic polyelectrolyte complexation and the formation of polyelectrolyte multilayers are physically similar processes, my further activity in this direction will be aimed at the rationalization of regularities controlling the growth of thin multilayer films that are widely used as biocompatible and antimicrobial coatings.

(ii) Conformations and Electronic Properties of (Ionic) Conjugated Polymers

Electronic properties of conjugated polymers are defined by the interplay between the interchain and intrachain diffusion of mobile charge carriers. The extent to which interchain diffusion translates into the sample conductivity dramatically depends on the polymer conformations, i.e., on the chain stiffness, contour length, degree of liquid crystalline (nematic) order, and internal film structure. When chemically doped, conjugated polymers can be considered as polyelectrolytes, with the degree of doping not only controlling the density of the charge carries but also affecting chain conformations and local morphology of the film. Analysis of the film structure and polymer conformations in it is the problem of statistical physics of polymers. I will use analytical theory and computer simulations to predict the underlying structural and resulting electronic properties of neutral and doped conjugated polymers, thereby promoting the rational design of semiconducting polymer materials.

(iii) Order-Disorder Transitions in Intrinsically Disordered Proteins (IDPs)

It has been recently realized that IDPs are ubiquitous components of intracellular membraneless organelles, and the latter can be considered as the result of the liquid-liquid phase separation with the living cell. The formation of solid-like inclusions as the result of pathological protein aggregation within these organelles leads to neurodegenerative diseases but remains poorly understood. The disorder-to-order transition in IDPs, which is accompanied by the formation of alpha helices and beta sheets, is believed to be the main trigger for pathological aggregation. I will apply theoretical and simulation approaches revealing the role of IDP sequences (that may change as the result of mutations) and net charge (that depends on the external conditions, e.g., the degree of phosphorylation) in single-chain order-disorder transitions and the resulting protein aggregation. The first natural step is to start with the coarse-grained models of IDPs and consider the problem using well-established frameworks of polymer physics (e.g., coil-helix transitions). This approach was remarkably successful in describing the formation of liquid membraneless organelles: IDPs were considered as polyampholytes containing only three types of monomers – positively and negatively charged and neutral – and the effect of protein sequences, temperature, and salt concentration on their phase separation has been recently elucidated.

Teaching Interests

My teaching interests lie in the area of Polymer and Soft Matter Physics, Statistical Physics, Thermodynamics, and Molecular Engineering. At Moscow University, I had three years of experience as a teaching assistant for Statistical Physics of Macromolecules, Polyelectrolytes in Solutions and at Interfaces, and co-authored the teaching aids for these courses. I have successfully mentored undergraduate students during my PhD at Moscow University and graduate students during my postdoc at the University of Chicago.

Background

I received my Ph.D. in Physics in 2017 from Lomonosov Moscow University, Russia, working with Prof. Elena Kramarenko. Simultaneously, I was PhD student in DWI – Leibnitz Institute for Interactive Materials at RWTH Aachen University, Germany, where I worked under the co-supervision of Profs. Igor Potemkin and Martin Moeller. My graduate work was focused on the development of theories describing the swelling of polymer (micro)gels and their interactions with surfactants. During my first postdoc with Dr. Oleg Borisov and Dr. Ekaterina Zhulina in Pau, France, I worked on the theory of polyelectrolyte complex coacervation, intra-coacervate microphase separation, and the formation of micelles with complex coacervate cores. Currently, I am doing my second postdoc with Prof. Juan de Pablo at the University of Chicago. My recent theoretical and simulation activity is devoted to the different aspects of polyelectrolyte complexation, polyampholytes, and sequence-specific effects in polymers. To large extent, my research is done in the context of the collaboration with the experimentalists, including recent joint activity with the group of Prof. Matthew Tirrell.

Selected Publications

1. Rumyantsev, A. M.; Jackson, N. E.; de Pablo, J. J. Polyelectrolyte complex coacervates: Recent developments and new frontiers. Annu. Rev. Condens. Matter Phys. 2021, 12, 155-176.
2. Audus, D. J.; Ali, S.; Rumyantsev, A. M.; Ma, Y.; de Pablo, J. J.; Prabhu, V. Molecular mass dependence of interfacial tension in complex coacervation. Phys. Rev. Lett. 2021, 126, 237801.
3. Rumyantsev, A. M.; Jackson, N. E.; Yu, B.; Ting, J.; Chen, W.; Tirrell, M. V.; de Pablo, J. J. Controlling complex coacervation via random polyelectrolyte sequences. ACS Macro Lett. 2019, 8, 1296-1302.
4. Rumyantsev, A. M.; Zhulina, E. B.; Borisov, O. V. Scaling theory of complex coacervate core micelles. ACS Macro Lett. 2018, 7, 811-816.
5. Rumyantsev, A. M.; Pan, A.; Roy, S. G.; De, P.; Kramarenko, E. Yu. Polyelectrolyte gel swelling and conductivity vs counterion type, cross-linking density, and solvent polarity. Macromolecules 2016, 49, 6630-6643.

30+ publications total.