Research

Polyelectrolyte complex coacervates are liquid polymer-rich phases forming as the result of associative phase separation in mixed solutions of polyanions and polycations. Complex coacervation is considered one of the physical mechanisms behind the intracellular organization and formation of membraneless organelles. Coacervates of synthetic polyelectrolytes are promising underwater adhesives, and micelles with coacervate cores serve as efficient drug delivery vehicles. We apply the modern methods of polymer physics to predict the relationship between the structure of the polyelectrolytes and the properties of the coacervate phases. The interplay between charge connectivity and their long-range Coulomb interactions makes the physics of these systems very rich, beautiful, and challenging. Our interests include (but are not limited to) the intra-coacervate microphase separation, liquid crystalline ordering, the role of the primary sequence of monomers, and coacervation-driven self-assembly.

Charge carrier transport in conjugated polymers is controlled by the interplay of inter- and intra-chain hopping, which in turn is dependent on the polymer conformations. Introducing charges via intrinsic or extrinsic chemical doping enables beneficial tuning of the optoelectronic performance of the film. We apply scaling and field-theoretic methods of polymer physics to gain foundational predictions on the conformational statistics and conductivity of neutral and doped (ionic) conjugated polymers, providing a theoretical framework for the targeted design of soft electronic materials for flexible and stretchable electronic devices.   

Polyampholytes are macromolecules carrying both positively and negatively charged monomers. Historically, they were considered synthetic analogs of proteins. It is now established that almost 40% of the proteome comprises intrinsically disordered proteins (IDPs) or proteins with intrinsically disordered regions (IDRs). In contrast to the folded proteins, IDPs and IDRs are highly unstructured and undergo strong thermal fluctuations. This enables considering IDPs/IDRs as polyampholytes by applying the well-developed methods of the statistical physics of polymers. 

In globally non-neutral polyampholytes, the interplay between Coulomb correlation attractions of oppositely charged monomers and bare Coulomb repulsions between the chain segments due to their net nonzero charge results in an unusual type of conformations called necklaces. The necklace formation can be viewed as the microphase separation into collapsed globular (beads) and strongly extended (strings) regions within the single polyamholyte chain. We study how the necklace formation and structure are controlled by external conditions and the primary sequence of monomers.    

Genetic mutations and abnormal posttranslational modifications alter the primary sequence of IDPs and may induce changes in their conformational behavior, including the pathological transition of disordered regions to folded states. The latter is associated with multiple diseases, ranging from neurodegenerative disorders to cancer to cardiovascular problems. We are interested in developing simple physical models of IDPs, which enable considering conformational transitions in them theoretically and in coarse-grained simulations. Our goal is to derive a fundamental understanding of the relationship between the primary sequence of IDPs and their conformational behaviors, including disorder-to-order transitions that serve as a prerequisite for pathologic protein aggregation.  

Microphase separation in polymer melts and the formation of polymer micelles in solutions and at interfaces are different faces of the same phenomenon – polymer self-assembly. It is driven by thermodynamic factors and can be theoretically described. Theoretical polymer physics provides important guidelines, which enable controlling the size and morphology of the resulting structures by tuning the chain length, composition, and architecture. Separate attention is paid to electrostatically controlled microphase separation, where the finite size of microphase-separated domains is provided by the excess Coulomb energy of the domains, in contrast to the diblock copolymer microphases stabilized by chemical connectivity of the blocks. Another problem of interest is the diblock-copolymer micellization at the interfaces, where the reduced 2D dimensionality of the system results in unique and often unexpected behaviors.