Seminar - Scott Milner

Joyce Chair and Professor of Chemical Engineering

All dates for this event occur in the past.

130 Koffolt Laboratories, CBEC
130 Koffolt Laboratories, CBEC
151 W. Woodruff Ave
Columbus, OH 43210
United States

Scott Milner
Joyce Chair and Professor of Chemical Engineering
Department of Chemical Engineering
Penn State

Flow-Induced Crystallization and Nucleation in Isotactic Polypropylenes

Abstract

Flow-induced crystallization (FIC) occurs when a brief interval of strong flow precedes a temperature quench; many more nuclei form, resulting in a more fine-grained solid morphology with better material properties.  Common industrial polymer processing (particularly injection molding) depends on FIC, which has been the subject of many experimental studies, most commonly on isotactic polypropylene (iPP).  The prevailing hypothesis is that FIC results from flow aligning chains in the melt, increasing the melt free energy with respect to the crystal, hence acting like undercooling.  Here, I combine new experimental results for FIC and homogeneous nucleation with theoretical estimates for critical nuclei, to assess the prevailing hypothesis.  Current best information supports the view that chain stretching (not just alignment) is necessary and sufficient to explain the observed increase in nucleation rate.  Post-shear optical and atomic force microscopy suggests a change in crystallization mechanism above a threshold value of applied work.  Important puzzles remain:  1) shear applied at temperatures well above the equilibrium melting temperature is still effective for FIC; 2) a sheared sample may be held for hours above Tm, and still crystallize faster when finally quenched; 3) a sheared sample, remelted and quenched again, recrystallizes at a significantly higher temperature than an unsheared sample, a phenomenon that anneals away only very slowly.

Bio

Scott Milner joined the Chemical Engineering faculty at Penn State University in January 2008, where he holds the William H. Joyce Chair. Milner was a research physicist at ExxonMobil Corporate Strategic Research from 1989 to 2008. He received his Ph.D. in theoretical condensed-matter physics from Harvard University in 1986, after which he held postdoctoral positions at Exxon and AT&T Bell Labs before returning to Exxon in 1989. In 1993 Milner was awarded the John H. Dillon Medal of the American Physical Society for work on polymer brushes, copolymer mesophase ordering, and effects of flow on polymer solutions. He is an APS Fellow, served on the Executive Committee of the APS Division of Polymer Physics from 1999-2003, and as division councillor from 2006-2012.

Longstanding interests include polymer brushes, copolymer mesophases, effects of flow on complex fluids, and polymer rheology. Current research areas are polymer entanglement (including the topological origin of the tube, and “seeing” the tube and entanglements in simulations); glassy systems (including glass transitions in dense fluids, and lattice models of jamming); ordering and crystallization (including twist solitons, nucleation in polymers, and flow-induced crystallization); and materials for energy and electronics (including lithium transport in polymer electrolytes, and self- assembly and electronic transport in block copolymer photovoltaics).

 

 

 

Category: Seminar