ChBE Seminar Series: Alexandros Chremos, NIST
Speaker: Alexandros Chremos, Postdoctoral Researcher at NIST
Title: Solvation effects in (poly)electrolyte solutions
Most polymers encountered in living systems are polyelectrolytes because of their solubility in water, and this broad class of polymers is also ubiquitous in commercial materials in which water solubility is required; examples include hydrogels in diapers and gene delivery, thickeners in food industries, drug delivery, water purification agents, and cosmetics. While, it is widely appreciated that highly charged particles having the same charge to form dynamic clusters in solution, an accepted theoretical framework which accounts for this ubiquitous phenomenon, has been slow to develop. The theoretical difficulties are especially great for flexible polyelectrolytes due to the additional complex coupling between the polyelectrolyte chain configurations and a diffuse 'polarizable' cloud of counter-ions around these polymers. This effect has significant implications for the function of proteins and other natural occurring polyelectrolytes (e.g., DNA), as emphasized long ago by Kirkwood and coworkers. To probe this effect, we perform molecular dynamics simulations based on a coarse-grained model of polyelectrolyte solutions with an explicit solvent. Our findings demonstrate that the solvent is responsible for heterogeneous structure formation in salt-free polyelectrolyte solutions, revealing the essential role of the solvent interactions with the charged species in the description of the polyelectrolyte solutions. These findings are also closely related to relative simple case of electrolyte solutions, where the strength of solvent interaction with ionic species dictates the location of the ion along the Hofmeister series and modulating the solution properties of these solutions such as viscosity, density, and surface tension. Overall, our approach provides a guideline for the development of a more predictive theory of the properties of the thermodynamic and transport properties of these complex fluids.