Event
CHBE Seminar: Dr. Sachin Velankar, Pitt
Friday, March 27, 2026
11:00 a.m.
Room 2108 Chemical and Nuclear Engineering Building
Patricia Lorenzana
301-405-1935
plorenza@umd.edu
"Liquids that Freeze When Mixed: Thermodynamics and Kinetics of Co-Crystallization of Polyoxacyclobutane with Water"
Abstract: Polyoxacyclobutane (POCB) with structure –[CH2-CH2-CH2-O-] has the remarkable ability to co-crystallize with water to form a hydrate, one of only two polymers that can form a crystalline hydrate. Yet, upon melting the hydrate, POCB/water mixtures phase-separate into two co-existing liquid phases. This makes POCB the only polymer known to co-crystalline with a molecule with which it is immiscible in the amorphous state. This talk will first explore the unusual – indeed unique – phase behavior of POCB-water mixtures across a range of molecular weights. We will then examine hydrate crystallization along two pathways: either starting from a single-phase liquid mixture of POCB and water, or from a two-phase mixture in LLE. Starting from a single-phase liquid mixture, bulk crystallization kinetics and spherulite growth velocities both slow down as the water content decreases far below the hydrate stoichiometry. This suggests that the excess POCB, which cannot crystallize, acts as an impurity and imposes a diffusion barrier to crystallization. Starting from a two-phase mixture in LLE, hydrate crystallization only occurs within the POCB-rich phase, and is sensitive to stirring. Increasing molecular weight dehydrates the polymer-rich phase, and therefore slows crystallization. Salt severely dehydrates the polymer-rich phase and also slows crystallization. The temperature-dependence of hydrate crystallization kinetics generally agrees with the Hoffman-Lauritzen model for homopolymer crystallization. To our knowledge, this is the first study of the kinetics of cocrystallization of any polymer with a small molecule.
The talk will conclude with a brief discussion of other research in the Velankar group on capillary phenomena in particulate systems, and the large deformation mechanics of polymer materials.
Biography: Sachin Velankar is a Professor in the Chemical Engineering Department at the University of Pittsburgh. At present, he is also a rotating Program Director in the Engineering-CBET division of the National Science Foundation. He completed his B.Tech at IIT-Bombay and Ph.D. at the University of Delaware, followed by post-doctoral positions at the Katholieke Universiteit Leuven Belgium and the University of Minnesota. Common themes in his research are the mechanics of soft materials, polymer science, capillary phenomena, and rheology. Current research topics include capillary phenomena in particulate systems, mechanics of thin films and tubes, arterial mechanics, and polymer crystallization.
