Dr. Jian Qin, Associate Professor in the Department of Chemical Engineering at Stanford University will give a seminar titled "Crossover Between Mean-Field and Critical Scaling Near the Gel Point" to the interested faculty and students at Discovery Park.

Abstract

Gelation of linear precursor chains via random crosslinking is accompanied by the formation of finite clusters. The number and size distributions of the clusters have been predicted by the Flory-Stockmayer mean-field theory, which neglects the formation of loops. The theory breaks down in the close vicinity of the gel point, and its predictions are replaced with a set of critical scaling exponents. We explore the crossover between the mean-field and critical scaling by conducting coarse grained simulations for a mixture of reversibly crosslinked precursors and clusters. Molecular weights, backbone stiffness, and monomer bulkiness of the precursors are tuned systematically. The simulated radii of gyration of clusters exhibits distinct behaviors, which collapse onto a master curve upon normalization by an emergent length scale, thermal blob. The thermal blob measures the magnitude of the excluded volume interaction, which mainly depends on the extent of inter-chain overlap. The master curve reveals a surprisingly gradual crossover between the mean-field and critical regimes and indicates that majority of the crosslinked systems of experimental interests fall within the critical regime.

Bio

Jian Qin is an Associate Professor in the Department of Chemical Engineering at Stanford University. He received B.S. and M.S. degrees in Materials Science from Tsinghua University, and his Ph.D. from University of Minnesota under the supervision of Profs. David Morse and Frank Bates. Following postdoctoral fellowships at Pennsylvania State University, with Prof. Scott Milner, and The University of Chicago, with Prof. Juan de Pablo, he joined Stanford University as a Terman Faculty Fellow in 2016. His research focuses on theoretical study of morphological and rheological behavior of polymeric fluids, electrostatic interactions in structured electrolytes, and surface charge polarization. He has held the Kadanoff-Rice Fellowship and has been recognized by the 3M Non-Tenured Faculty Award, the Hellman Faculty Award, the NSF CAREER Award, the ACS PMSE Arthur Doolittle Award, the ACS PMSE Young Investigator Award, the Tau Beta Pi (Stanford) Teaching Honor Roll, and the APS Dillon Medal.