2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session K05: Dillon Medal Symposium
3:00 PM–6:00 PM,
Tuesday, March 7, 2023
Room: Room 128
Sponsoring
Unit:
DPOLY
Chair: Wesley Burghardt, Northwestern University; Ali Dhinojwala
Abstract: K05.00001 : John H. Dillon Medal (2022): Stretched Polymer Physics and Rheology
3:00 PM–3:36 PM
Abstract
Presenter:
Vivek Sharma
(University of Illinois Chicago)
Author:
Vivek Sharma
(University of Illinois Chicago)
Stringiness, stickiness, and dispensing behavior of polymeric complex fluids are often assessed qualitatively by dripping from a nozzle or spoon or by stretching a liquid bridge between two surfaces (thumb and forefinger). Here the lifespan of pinching necks is determined by the response of polymers to extensional flows associated with streamwise velocity gradients that spontaneously arise within necks undergoing capillarity-driven thinning. Here we describe dripping-onto-substrate (DoS) rheometry protocols we developed to facilitate extensional rheology characterization even for lower viscosity fluids and at high extensional rates beyond the range of most commercially-available methods. Using DoS rheometry protocols, we pursue various intertwined quests in stretched polymer physics including conformation-dependent hydrodynamic and excluded volume interactions, Pincus’ tension blobs, finite extensibility effects, as well as coil-stretch transition and hysteresis. We observe that the extensional relaxation times exhibit concentration-dependent variation distinct from shear rheology response measured using shear rheometry or anticipated by blob models developed for the relaxation of weakly perturbed chains. We show that the influence of molecular weight and chemistry can be evaluated a priori using three macromolecular parameters: flexibility, extensibility, and segmental dissymmetry for neutral polymers. Finally, we characterize and analyze the pinch-off dynamics of charged polymers to elucidate the influence of the complex interplay of electrostatic and hydrodynamic stretching of macromolecules and demonstrate how the changes in salt or solvent influence stretched polymer physics. We identify the stretched overlap concentration below which the extensional relaxation time is concentration-independent and a spinnability concentration (below which only beads but no fibers appear) by accounting for the influence of higher extensibility of ultrahigh molecular weight fractions.