Professor Zhen-Gang Wang
Professor Zhen-Gang Wang
Department of Chemical Engineering
California Institute of Technology
Self-Assembly of End-Charged Block Copolymers and Blends: Effects of Ion Clustering
Introducing a small number of ionic groups at polymer chain ends — whether within a single diblock copolymer or across two different homopolymers in a blend — has emerged as a promising strategy for directing self-assembly, with applications ranging from compatibilizing immiscible polymer blends to templating functional and ion-conducting nanostructures. We study the effects of these end charges on the self-assembly of diblock copolymers and binary polymer blends using a self-consistent field theory that incorporates strong ion correlations. Under the low-dielectric conditions typical of polymer melts, the charged ends aggregate into multi-ion clusters, which reshapes the self- assembly of both systems. In the case of end-charged diblock copolymers, the resulting clusters act as compact, curvature- favoring foci around which the chains radiate, unlocking complex network morphologies, such as the single primitive and single gyroid phases, that are normally inaccessible to neutral melts. In binary blends with oppositely charged termini, the electrostatic attraction between chain ends suppresses the macroscopic phase separation in the corresponding uncharged blend and results in microphase separation instead. Interestingly, the resulting phase diagram is simpler — dominated by lamellar and cylindrical phases — than expected based on the pairwise-bonded effective diblock picture previously invoked to describe these systems. We attribute this difference to the difference in the location of the ion clusters in the two systems: in the diblock they act as compact foci to organize the chains around them, while in the blend they are confined to the interface separating the two species, where they resist curvature rather than favor it. Finally, for both systems, ordered microphase structures can appear at segregation strengths significantly lower than that required for the corresponding uncharged diblock copolymers.
Zhen-Gang Wang
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 a member of the U. S. National Academy of Engineering. He 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). 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.
Hosted by Professor Timothy Lodge
