Events

Polymer–ionic liquid (IL) mixtures are promising materials for applications ranging from battery electrolytes and gas separation membranes to responsive actuators and sensors, owing to their unique combination of mechanical robustness and ionic conductivity. These systems often exhibit lower critical solution temperature (LCST) behavior and more symmetric phase envelopes than anticipated from the classical Flory–Huggins theory. In this work, we investigate the molecular origins of this anomalous behavior by systematically incorporating clustering, polymer–cation binding and electrostatic correlations into a simple thermodynamic framework. Our analysis reveals that the formation of clusters contributes to demixing at low temperatures, contrary to both experimental observations and prior theoretical predictions. In contrast, electrostatic interactions introduce persistent asymmetries in the free energy landscape, yielding different chain-length scaling in the critical composition and interaction parameter than predicted by the Flory–Huggins theory.  Based on these insights, we propose a minimal, physically grounded model incorporating only mixing entropy, temperature-dependent Flory–Huggins parameter, and electrostatic correlation. This model successfully reproduces key experimental features in systems such as PEO + [EMIM][BF₄], using a small set of interpretable parameters. These results offer a mechanistic understanding of the phase behavior of polymer–IL mixtures and provide a practical modeling framework for their design and optimization.

Zhen-Gang Wang received his B.Sc. in Chemistry in 1982 from Beijing (Peking) University, and his Ph.D. in Chemistry in 1987 from the University of Chicago. He did postdoctoral research first in Exxon Research and Engineering Company and then at UCLA.  Since 1991 he has been on the Chemical Engineering faculty at the California Institute of Technology, where he is currently the Dick and Barbara Dickinson Professor.  He has also served as Executive Officer (department chair) for Chemical Engineering for 6 years.

Wang’s research is the theoretical and computational study of structure, phase behavior, interfacial properties and dynamics of polymers, soft materials, and biophysical systems. His current activities revolve around three main themes: charged systems, including polyelectrolytes, salt-doped polymers, and electric double layers; nucleation or more generally barrier crossing in polymers and soft matter; and nonlinear rheology of polymer gels and entangled polymers.

Wang is a fellow of the American Physical Society and is recipient of several significant awards and honors, including the Camille Dreyfus Teacher–Scholar Award (1995), the Alfred P. Sloan Award (1996), the Braskem Award from the American Institute of Chemical Engineers (AIChE) (2018), the AIChE Alpha Chi Sigma Award (2023), and the American Physical Society Polymer Physics Prize (2024).  He was recently elected a member of the National Academy of Engineering (2025).  In addition, he was awarded the Richard P. Feynman Prize for Excellence in Teaching (2008), Caltech’s highest teaching honor.

Wang has served on the editorial advisory boards of Journal of Theoretical and Computational Chemistry, Macromolecules, ACS Macro Letters, Giant, Acta Physicochimica Sinica, and Science in China B (Chemistry). He is currently an associate editor for the ACS Journal Macromolecules.