Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P03: Dynamics and Rheology of Polymers and Polyelectrolytes IFocus Live
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Sponsoring Units: DPOLY DSOFT GSNP DBIO Chair: Vivek Sharma, University of Illinois at Chicago |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P03.00001: Hydrodynamic Interactions in Topologically Linked Ring Polymers Phillip Rauscher, Stuart Rowan, Juan De Pablo Despite decades of interdisciplinary research on topologically linked ring polymers, their dynamics remain largely unstudied. These systems represent a major scientific challenge as they are often subject to both topological and hydrodynamic interactions (HI), which render dynamical solutions either mathematically intractable or computationally prohibitive. Here we circumvent these limitations by preaveraging the HI of linked rings. We show that the symmetry of ring polymers leads to a hydrodynamic decoupling of ring dynamics. This decoupling is valid even for nonideal polymers and nonequilibrium conditions. Physically, our findings suggest that the effects of topology and HI are nearly independent and do not act cooperatively to influence polymer dynamics. We use this result to develop highly efficient Brownian dynamics algorithms that offer enormous performance improvements over conventional methods and apply these algorithms to simulate catenated ring polymers at equilibrium, confirming the independence of topological effects and HI. The methods developed here can be used to study and simulate large systems of linked rings with HI, including kinetoplast DNA, Olympic gels, and poly[n]catenanes. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P03.00002: Dynamics and rheology of bidisperse polymer melts through a simplified molecular model Oluseye Adeyemi, Li Xi Polydispersity is inevitable in industrially produced polymers. Established theories of polymer rheology mostly apply to monodisperse linear polymers. Dynamics of polydisperse polymers is yet to be fully. In this study, we focused on bidisperse polymers of different compositions as an idealized model system and used a coarse-grained molecular model to explore their dynamics and rheology. Specifically, we considered the effects of longer chains on shorter chains and vice versa in the mean-squared displacement, relaxation spectrum and viscoelasticity. Our simulation results show that longer chains do not have any significant effect on the dynamics of shorter chains regardless of their concentration, while shorter chains serve to speed up the relaxation of longer chains. We further conducted a Rouse Mode Analysis on these systems and found that the relaxation rate of the shorter chains shows a dependence on the concentration of the longer chains, which generally increases with an increased concentration of the latter. Simulation results were also used to evaluate semi-empirical mixing rules proposed in the literature for the prediction of the rheology of polydisperse polymers based on monodisperse rheology and found the results to reasonably predict the rheology of the mixture. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P03.00003: Recovery of stress overshoot under orthogonal shear after interrupted shear flow Marco Galvani, Peter Olmsted, Mark Owen Robbins Both entangled and unentangled polymer melts exhibit stress overshoots when subject to shear flow. The size of the overshoot depends on the applied shear rate and is related to relaxation mechanisms such as reptation, chain stretch and convective constraint release. Previous experimental work shows that melts subjected to interrupted shear flows exhibit a smaller overshoot when sheared again after allowing for some relaxation. The time scale for recovery of the maxima is about the timescale for relaxation of the stress for unentangled melts but is significantly longer for entangled melts. Here, we show results of molecular dynamics simulations of interrupted shear of polymer melts where the shear flow after the relaxation stage happens in an orthogonal direction to the original flow. We observe that the size of the stress overshoot is larger than predictions by the Rolie-Poly model, and larger than observed during a second shear in the same direction as the original for the same relaxation time. Similar differences are also observed in transient behavior of the normal stresses, chain end-to-end distance and number of entanglements per chain. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P03.00004: Predicting the plateau modulus from molecular parameters of conjugated polymers Abigail Fenton, Enrique D Gomez, Ralph Colby The relationship between Kuhn length b, Kuhn monomer volume v0, and plateau modulus GN° initially proposed by Graessley and Edwards and experimentally investigated by Everaers, while well-studied for flexible and stiff polymers, has a large gap in experimental data between the flexible and stiff regimes. This gap prevents the validation of the crossover between flexible and stiff polymers and therefore, the prediction of mechanical properties from chain structure of any polymer in this region. Given the chain architecture, including a semiflexible backbone and side chains, conjugated polymers are an ideal class of material to study this cross-over region. Using small angle neutron scattering, oscillatory shear rheology, in-situ polarized optical rheology, along with the freely rotating chain model, we have shown that twelve polymers with aromatic backbones, including conjugated polymers, populate a large part of this gap. We also have shown that a few of these polymers exhibit nematic ordering, which explains a lower experimental GN° than predicted using Everaers’ plot, as nematic polymers have fewer entanglements than isotropic polymers. Nevertheless, when isotropic, these polymers follow the proposed relationship between b, v0, and GN°. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P03.00005: Model for flow-induced crystallization of industrial-grade LLDPEs Marat Andreev, David A Nicholson, Gregory Rutledge, Anthony Kotula, Kenneth Kearns, Jonathan Moore, Jaap den Doelder Flow-induced crystallization (FIC) is ubiquitous in the manufacturing of semi-crystalline plastic products. Generally speaking, polymer crystallization and polymer rheology operate on very different time and length scales. Therefore, modeling FIC requires a multi-scale approach. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P03.00006: Solvent-induced Collapse Transition in Kinetoplast DNA sheets Dave Holling, Alexander R Klotz Kinetoplasts are complex DNA structures consisting of circles that are linked together to form a network which resembles chain-mail armor. There is theoretical interest in the behavior of 2D materials, including thermally-induced crumpling. Kinetoplasts can serve as a model 2D polymer where their size, as determined by optical fluorescence microscopy, can vary depending on solvent quality, where water serves as a good solvent and ethanol as a poor solvent. We aimed to observe the 2D version of the coil-globule transition by measuring diffusivity and radius of gyration of kinetoplasts as a function of ethanol concentration. We observed a transition in the kinetoplast's shape at around 60-70% ethanol in solution, below which they appear as curve membranes and above which they appear as compact globules. More quantitative measurements of duplicated kinetoplasts will allow precision measurements of the universal size scaling exponent as a function of solvent quality. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P03.00007: Dynamic transistion to isostaticity induces complex stress response in DNA nanostar networks Nathaniel Conrad, Alexander L Bevier, Deborah Kuchnir Fygenson, Omar A. Saleh Transiently cross-linked biopolymer networks (e.g. actin-actinin networks) exhibit a complex stress response markedly different from that of a simple Maxwell material. They both flow and support stress over several decades of low to intermediate frequencies. Here, we perform oscillatory rheology on networks made of 6-armed DNA nanostars (NS) whose designable interactions allow us to investigate the role of cross-linker lifetime on the complex stress response. When three of the arms have short-lived bonds (α-bonds) and the other three have longer-lived bonds (β-bonds) (e.g., α3β3 NS), the network exhibits a complex stress response persisting over a broad range of frequencies determined by the respective short-lifetime and long-lifetime bonds. We hypothesize the existence of a dynamic transition from a sub-isostatic network at low frequencies to an isostatic one at high frequencies to explain the complex stress response. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P03.00008: Local Hydrodynamics and Chain Architecture in Flowing Semidilute Polymer Solutions Charles Young, Charles Sing It is important to understand the dynamics and rheology of semidilute polymer solutions at a molecular level, because out-of-equilibrium polymer conformations that arise due to strong processing flows can impact material properties in a variety of applications. Despite this practical importance, it remains a challenge to predict how concentration, flow, hydrodynamic interactions (HI) and architecture all govern the dynamics of semidilute polymer solutions. This is particularly true in simulation, where it is computationally expensive to include long-range HI effects that are crucial to capturing the dynamics of polymer solutions, both in and out-of-equilibrium. We developed an iterative conformational-averaging (CA) method for performing these calculations, circumventing a number of computational bottlenecks to enable the large-scale simulation of polymer solutions in flow. CA calculations demonstrate the importance of HI in semidilute solutions, revealing the effect of ‘local hydrodynamics’ that enhance conformational fluctuations in planar elongational flows. HI is also shown to couple to polymer architecture, in both ring and branched polymers, in a variety of unexpected ways that have implications in conformational relaxation and polymer-polymer ‘hooking’. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P03.00009: Macromolecular engineering of pinching dynamics, extensional rheology and processability Vivek Sharma, Jelena Dinic, Leidy N Jimenez, Carina Martinez We elucidate the influence of chemical structure on macromolecular hydrodynamics, rheological response, and drop formation/liquid transfer. We contrasting the shear and extensional rheology response of aqueous solutions of semi-flexible 2-hydroxyethyl cellulose (HEC) with solutions of flexible, polyethylene oxide (PEO). We critically analyze the radius evolution data obtained using Dripping-onto-Substrate (DoS) rheometry to argue that the solutions of flexible PEO macromolecules exhibit signatures of underlying coil-stretch transition not observed for the solutions of semi-flexible HEC. We distill out how length, diameter and number of Kuhn segments affects macromolecular dynamics, rheological response and processability, and infer that the ratio of packing length to Kuhn length, a parameter we term as segmental dissymmetry, helps to hone in on the contrast related to flexibility and extensibility, that are determined by chemical structure for macromolecules comparable molecular weight. |
Wednesday, March 17, 2021 4:48PM - 5:24PM |
P03.00010: Thinning and breakup of freestanding polymer films Invited Speaker: Jan Vermant Freestanding liquid films present an interesting environment for polymer chains in solution, as the chains are confined while being subjected to capillary and hydrodynamic stresses, with relevance for foaming processes. In the present work we first discuss how polymer solution films provide ideal model system to study the hydrodynamic breakup regime of thin liquid films and how the critical thickness is controlled by both material properties and hydrodynamic conditions. Second, we provide evidence that such thin films of polymer solutions can be stabilized through lateral, osmotic-based transport of polymer chains to produce several of the phenomena that are associated with interfacial, Marangoni-based stresses. Phenomena such as cyclic dimple formation, vortices, and dimple recoil were observed. The factors which lead to enhanced lifetime of the films as a consequence of these flow instabilities can be used to either stabilise foams or, conversely, prevent foam formation. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P03.00011: Heterogeneous Rouse Model for Polymer Dynamics and Linear Rheology in the Time-Temperature-Superposition-Breakdown Regime David Simmons, Peijing Yu Time-temperature superposition breaks down in many polymers upon approach to the glass transition temperature Tg. Because TTS is fundamentally rooted in the Rouse model prediction of a shared temperature dependence for chain and segmental relaxation modes, this breakdown implies a significant gap in our understanding of polymer dynamics at low temperature. Here, we report on tests against experiment of the Heterogeneous Rouse Model, which generalizes the Rouse model to incorporate the emergence of a distribution of segmental relaxation times at low temperature. The Heterogeneous Rouse Model predicts a compression of the Rouse regime in complex and relaxation moduli with increasing dynamic heterogeneity at lower temperatures. These predictions are found to be in agreement with observed polymer linear rheological response in the TTS-breakdown regime, suggesting that this theory provides a promising model for polymer TTS breakdown near Tg. |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P03.00012: Crossover from Rouse to entangled polyisoprene dynamics: a multiscale simulation approach Wei Li, Alireza Behbahani, Craig Burkhart, Patrycja Polinska, Vagelis Harmandaris, Manolis Doxastakis Topological constraints govern the dynamics of entangled macromolecules when polymers exceed a critical molecular weight. The crossover from the low molecular limit described by the Rouse model to dynamics prescribed by entanglements has long been the subject of extensive research with significant challenges present. Constraint release and contour length fluctuations are often introduced into phenomenological descriptions to capture dynamics that depart from the original Doi-Edwards tube theory. However, significant recent studies find that many of these features present chemically specific characteristics rather than a ubiquitous behavior, questioning therefore our comprehensive understanding of the fundamental underlying mechanisms. Polyisoprene melts have long served as a prototype experimental system to study the evolution of the end-to-end distance along with mechanical relaxation. In this study, we present new results by a systematic investigation of the transition of polyisoprene molecules from the Rouse regime to dynamics dictated by topological constraints. We report findings on mean correlation times as well as a complete description of full relaxation spectra and contrast our data to experimental studies. |
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