Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G19: Revealing the Microscopic Dynamics Driving Nonlinear Polymer FlowsInvited
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Emanuela Del Gado, Georgetown University Room: 207 |
Tuesday, March 3, 2020 11:15AM - 11:51AM |
G19.00001: Self-Healing Recovery and Dynamics of Associating Polymers under Uniaxial Extension Invited Speaker: Nicolas Alvarez Associating polymers are a desirable class of materials with intrinsic abilities to self-heal without the need for additional components or added stimulus. While experimental and theoretical measurements of recovery exist in the literature, quantifying recovery in terms of fundamental rheological parameters is often difficult. In this work we use filament stretching uniaxial extension to probe the recovery of unentangled and entangled hydrogen bonding polymers. Using a novel methodology, we confirm the role of process timescales such as the time before and after recovery on both the transient rheology and ultimate recovery of associating polymers. Furthermore, we show the importance of architecture and molecular timescales of the network on recovery. We find that while strongly associating groups provide improved mechanical strength, they often delay the process of recovery. Additionally, we show that the presence of entanglements has a complex role on recovery, introducing the flow timescale as an additional parameter. With this work, we develop a framework that is both useful for evaluation of self-healing soft materials and for design of novel self-healing polymers. |
Tuesday, March 3, 2020 11:51AM - 12:27PM |
G19.00002: Decoding the viscoelastic response of monodisperse and bidisperse linear polymers under uniaxial extension Invited Speaker: Evelyn van Ruymbeke Predicting the linear viscoelastic properties of linear polymers has reached a quantitative level, based on mesoscopic approaches such as slip-link models or the Doi-Edwards tube-model theory combined with established relaxation mechanisms such as reptation, contour length fluctuations and constraint release. A consistent molecular picture could be proposed for describing the linear regime, which allows explaining the different experimental data based on the same framework. In particular, in case of polymer chains diluted in an oligomer matrix, the universality of linear viscoelastic response of polymers has been demonstrated with different chemical structures and concentrations: as long as the chains contain the same number of entanglements, their normalized viscoelastic properties will the be same. |
Tuesday, March 3, 2020 12:27PM - 1:03PM |
G19.00003: Evidence of Flow-Induced Crystallization in Material Extrusion Additive Manufacturing Invited Speaker: Anthony Kotula Material extrusion additive manufacturing processes force molten polymer through a printer nozzle at high (>100 s−1) shear rates prior to cooling and crystallization. This can lead to flow-induced crystallization in common polymer processing techniques, but the magnitude of this effect is unknown for additive manufacturing. Here, we will show the effect of the material extrusion on the morphology of poly(lactic acid), a common semicrystalline polymer used in material extrusion. The talk will encompass materials characterization (rheology and crystallization kinetics) relevant to printing, process line temperature measurements, and polarized optical microscopy techniques to characterize the final microstructure, which we compare with continuum modeling. Although no crystalline domains are seen in the as-printed part, a post-print annealing process reveals spherulitic domains with sizes that dramatically decrease near the weld line. Our results show that residual chain stretch from the extrusion and deposition process enhances the nucleation rate in the weld regions between extruded layers. The higher nucleation density in these regions is not obvious in the as-printed part but is revealed only through the annealing process, which is captured in the model. |
Tuesday, March 3, 2020 1:03PM - 1:39PM |
G19.00004: How the Microscopic Dynamics of Different Polymer Architectures Drive Nonlinear Extensional Flows Invited Speaker: Thomas O'Connor Many industrial processes elongate polymer liquids at rates much faster than the molecular chain's characteristic relaxation times. These nonlinear extension flows can strongly deform microscopic polymer conformations and drive dynamic transitions that produce large changes in polymer viscosity. Understanding how flow depends upon and drives such changes in polymer microstructure is essential for improving established and emerging fabrication methods like fiber spinning and 3D printing. However, most microscopic understanding of these nonlinear flows has been drawn from indirect techniques that infer molecular dynamics from macroscopic rheology. This has begun to change with the recent development of new experimental and numerical simulation techniques that allow researchers to control, sustain, and microscopically probe polymer dynamics during strong extension. Here, I’ll present molecular simulations for linear, star, and ring polymer melts and blends deformed in uniaxial extensional flow. In all three cases, coarse-grained molecular dynamics simulations reproduce the nonlinear rheology observed in extensional flow experiments, and also reveal the microscopic dynamics driving observed nonlinear trends. For some architectures, simple theoretical arguments can directly relate the elongated conformations of molecules to the nonlinear viscosity. In other cases, simulations show how extensional flows can drive polymers to topologically self-assemble or micro-phase separate in ways not seen in equilibrium. These new, far from equilibrium behaviors could provide new routes for controlling polymer microstructure during processing. |
Tuesday, March 3, 2020 1:39PM - 2:15PM |
G19.00005: Polymer Scission in Contraction Flows Invited Speaker: Peter Olmsted Polymer scission has been studied for many years! It has numerous practical implications in areas such as drug injection, spraying and printing, and oilfield harvesting. When injected through a contraction flow, high molecular weight polymer solutions exhibit a sharp increase of apparent viscosity due to chain stretching during fluid extension. This stretching can induce polymer scission, which then decreases the extensional viscosity. We revisit this old problem using specially-designed microfluidic hyperbolic contraction flows. We study the pressure-flux relation for high molecular weight polymer solutions passing through the contraction, and find that the ratio of the pressure drop to that of the (Newtonian) solvent has a maximum due to the competition between polymer extension and degradation (scission). From the dependence of the pressure maximum on flow rate and molecular weights we can quantify the decrease in equivalent molecular weight due scission in the contraction. We find a geometry-dependent quasi-universal relation between the flow rates at which the maximum occurs for successive passage in a given contraction, which appears to be independent of molecular weight, concentration, solvent quality and viscosity, and can be used to predict degradation under successive passes. I will discuss what we can learn about the the details of the scission kinetics in flow from these observations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700