Seminar: Dr. Jian Qin, Stanford University
Effects of Connectivity, Polarity and Stoichiometry on Charge-driven Assembly
The electrostatic interaction in structured fluid, being long-ranged, is sensitive to a variety of short-ranged features including molecular polarity and dielectric heterogeneity. After recapitulating the basic notions that capture these local effects, we focus on the modeling of polyelectrolyte complexation. Through a joint theoretical and experimental effort, we show that charge connectivity, backbone polarity, and stoichiometry all markedly impact the demixing instability of polyelectrolyte solutions. In particular, stoichiometry asymmetry leads to a looping-in complexation window, in which adding salts causes the polymers to salt out, contrary to the salting-in behavior commonly observed. Aided with dual-fluorescent labeling and elemental mapping, we unambiguously measured the concentrations of four ionic species in both coexisting phases and rationalized the partition coefficients by considering the competition of ion entropy and strength of electrostatic screening.
Jian Qin received B.S. and M.S. in materials science from Tsinghua University, and Ph.D. from the department of Chemical Engineering and Materials Science at University of Minnesota. Following postdoc trainings at Pennsylvania State University and University of Chicago, he joined the faculty in Chemical Engineering at Stanford University in 2016. His research focuses on theoretical modeling of morphological and rheological behaviors of polymeric fluids, electrostatic interactions in structured electrolytes, and surface charge polarizations. His recognition includes Kadanoff-Rice fellowship, 3M Non-Tenured Faculty Award, Hellman Faculty Award, NSF CAREER Award, ACS PMSE Young Investigator, ACS PMSE Arthur Doolittle Award, and Tau Beta Pi (Stanford) Teaching Honor Roll.