Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G23: Nonequilibrium Structures and Dynamics of Polymeric Materials IIFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Tad Koga, Stony Brook University Room: Room 215 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G23.00001: Simulation of Molecular Bottlebrush Relaxation Dynamics by DPD with Proper Orthogonal Decomposition Michael J Hore Molecular bottlebrushes (BBs) form from a dense grafting of side chains to a macromolecular backbone and can be synthesized in several ways -- including by atom-transfer radical polymerization (ATRP) or ring-opening metathesis polymerization (ROMP). BBs have received considerable attention in recent years due to unique physical properties that result from their architecture. For example, BBs possess very large entanglement molecular weights compared to traditional linear polymers and are typically unentangled. The conformation of BBs, along with their relaxation dynamics, play major roles in determining the physical properties of materials they comprise. Here, we discuss recent results from dissipative particle dynamics (DPD) simulations of BBs as a function of their backbone length, grafting density, and interactions with their local environment. Analyzing the relaxation dynamics is more challenging for BBs than for linear polymers because the eigenbasis used for Rouse mode analysis of linear chains does not produce the normal coordinates of the BB monomers. Using proper orthogonal decomposition (POD), we numerically calculate the eigenbasis for BBs, compare it to linear chains, and offer some interpretation of the first few modes. Finally, we discuss how the relaxation times of the BBs scale with backbone length, grafting density, and other relevant parameters. The results of our simulations are compared with experimental investigations in the literature. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G23.00002: Molecular-Weight Dependence of Center-of-Mass Chain Diffusion in Polymerized Ionic Liquid Melts Peng Lan, Qiujie Zhao, Guangxin Lv, Grant S Sheridan, David G Cahill, Christopher M Evans Polymerized ionic liquids (PILs) with flexible polymer chains and weakly-interacting ionic liquid (IL) groups exhibit desirable properties like moderate ion conductivity, and have received great attention in applications of energy storage/conversion, stimuli-responsive materials, etc. However, less is known about their dynamic properties such as viscosity and chain diffusion, which are also important in the context of 3D printing, electro-adhesion and calculating free ion transference numbers. In this work, the center-of-mass diffusion of solvent-free, fully-charged PILs were probed using fluorescent recovery after photobleaching (FRAP). A series of acrylic PILs with imidazolium cations and bis(trifluoromethanesulfonyl)imide (TFSI) anions (TFSI-f-PILN) were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization with precise control of degrees of polymerization N ranging from 40 to 236. A fluorescent acrylate monomer with the 7-nitrobenzofurazan group was copolymerized into polymer backbones at trace levels as a probe of chain motion. The diffusion coefficient (D) of TFSI-f-PILN was determined by fitting diffusion model into fluorescence intensity profiles obtained from post-bleaching images. Within the uncertainty of 3~20 %, a scaling relationship of D~N-2 was observed which is consistent with the scaling of linear neutral polymers. Wide-angle X-ray scattering exhibited no peak at ~5 nm-1 for the long-range imidazolium-TFSI ionic aggregation. The results indicated the molecular weight dependence of center-of-mass diffusion is not impacted by the electrostatic interactions of IL groups. But no transition from the Rouse regime (D~N-1) to reptation regime (D~N-2) was observed within the studied N range. We hypothesized that the single diffusion coefficient scaling trend is due to the increased stiffness of present PILs compared with their neutral analogues as the bulky ionic groups will impact the conformations of chains. This work provided a fundamental insight into the chain length dependence of diffusion dynamics of ionic polymer melts and also proposed a general method to study center-of-mass diffusion in dry ionomers. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G23.00003: On the molecular origin of the Slow Arrenhius Processes (SAP) responsible for fast equilibration of polymer melts Simone Simon Napolitano Growing experimental evidence indicates the presence of equilibration pathways exhibiting a temperature-invariant activation energy on the order of 100 kJ/mol. By exploiting the Onsager regression hypothesis, we identified the underlying molecular process responsible for this class of Arrhenius equilibration mechanisms with a slow mode (SAP), universally present in the liquid dynamics [1]. The SAP, which we show is intimately connected to high temperature flow, can efficiently drive melts and glasses towards more stable, less energetic states. Based on new experimental evidence, we propose that the SAP originate from rearrangements within a set of molecules organized in clusters which are less sensitive to density than the structural process, and do not undergo a glass transition. Measurements in nanoconfined polymer provided information on the volume distribution of the clusters and their average size. Depending on the system investigated, such clusters extends from several tens of nanometers up to more than a micron. We anticipate a correlation between the characteristic lengthscale of the SAP and its efficiency in equilibrating polymer melts. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G23.00004: Dynamic density functional theory for entangled polymer mixtures Friederike Schmid, Bing Li, Alireza F Behbahani The dynamic density functional (DDF) theory is an efficient method to |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G23.00005: Understanding molecular deformation and relaxation of ionomers by complementary small-angle scattering techniques Yangyang Wang, Christopher N Lam, Wei-Ren Chen The molecular relaxation dynamics of rubidium neutralized sulfonated polystyrene ionomers after a large step uniaxial extension are investigated by small-angle neutron (SANS) and x-ray (SAXS) scattering techniques. Due to the different scattering contrast for neutrons and x-rays, the nonequilibrium structures of polymers and ionic clusters are revealed by SANS and SAXS, respectively. It is found that the single-chain structure becomes highly anisotropic upon deformation, whereas the ionic structures hardly show any distortions. This observation stands in stark contrast to the classical transient network picture, where the physical crosslinks formed by ionic clusters drive the molecular deformation of the polymer chains. Further analysis of the SAXS spectra indicates that small ionic clusters form fractal aggregates, which provide structural rigidity to resist the applied deformation. Moreover, quantitative analysis of the SANS using the spherical harmonic expansion technique shows that the presence of molecular association fundamentally alters the spatiotemporal dependence of the structural anisotropy relaxation relative to the near polymers, with much stronger wavenumber dependence for the associating chains. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G23.00006: Coarse-Grained Molecular Dynamics Simulation of Poly(dimethyl-co-diphenyl) Siloxane: Chain Dynamics of Unentangled and Entangled Melts Weikang Xian, Amitesh Maiti, Andrew P Saab, Ying Li Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, as its versatility and properties lead to many applications. The incorporation of phenyl siloxane, via copolymerization, for example, has been proposed to improve the mechanical properties of PDMS. However, such copolymerization changes the microscopic structural and dynamic properties of the copolymers significantly. We recently used all-atomistic molecular dynamics (AAMD) simulation to study the properties of unentangled linear poly(dimethyl-co-diphenyl) siloxane random copolymer melts, where it was shown that as the molar ratio of the diphenyl content φ increases the chain dynamics slow down by over two orders of magnitude. On the other hand, understanding the properties of copolymers with a higher degree of polymerization (i.e., above the entanglement length) is extremely important. However, an all-atomistic exploration of such an entangled system becomes very challenging due to slow relaxation, especially in presence of phenyl groups. In this work, we addressed this problem using a coarse-grained molecular dynamics (CGMD) approach to investigate the structural and dynamic properties of long-chain copolymers. First, we optimized the CG potentials by iterative Boltzmann inversion (IBI) to ensure that the CGMD model preserves the configurations and microstructures of the copolymer. We then built and equilibrated systems with different chain lengths and molar ratios of the diphenyl content (φ). Relation between the molar ratio φ and the structural properties of the entangled copolymer, such as tube diameter and entanglement density, were revealed by Z1 analysis. More importantly, the reptation-tube-like dynamics of the copolymer were closely studied. As expected, the chain dynamics of the entangled copolymer was found to slow down significantly with increasing φ. However, we found that such deceleration is due not only to the increased local friction of the phenyl groups but also to the complex structure-dynamics interaction within the copolymer environment. |
Tuesday, March 7, 2023 12:42PM - 1:18PM |
G23.00007: Nonlinear Rheology of Unentangled Polymer Melts Invited Speaker: Hiroshi Watanabe Nonlinear rheology of polymers has been extensively studied from both experimental and theoretical points of view. Transient stress overshoot followed by thinning, commonly observed for entangled melts and solutions under fast shear, is well described by advanced molecular models based on the tube/slip-spring concept. Nevertheless, under fast extension, strain-hardening is observed for entangled solutions but not for entangled melts, and those models cannot explain this difference between the solution and melt. This problem has been resolved by Ianniruberto and coworkers who developed a concept of segmental friction (ζ) reduction occurring in a highly co-aligned environment in melts. The rapidly moving solvents are not oriented, which allows the entangled solutions to be free from the ζ-reduction thereby exhibiting the strain hardening. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G23.00008: A meso-scale simulation method for polymers J. Galen Wang, Daniel R Ladiges, Andy Nonaka, John B Bell, Alejandro L Garcia
|
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G23.00009: Effect of Submicron Structures on the Mechanical Behavior of Polyethylene Mikihito Takenaka, Mizuki Kishimoto Changes in submicron structures were found to affect the yielding behavior of polyethylene (PE) during tensile testing.The spatial inhomogeneity of the stress fields associated with density or crystallinity fluctuations on the submicron scaleenhanced the density fluctuation by a viscoelastic effect during stretching, resulting in the generation of voids. The amplitude of the spatial inhomogeneity of the submicron-scale stress field in linear low-density polyethylene (LLDPE) was smaller than that in high-density polyethylene (HDPE) due to the lower stability of the lamellar structures in the LLDPE under stretching. Thus, in the LLDPE case, the generation of voids and necking occurred after the enhancement started so that the LLDPE exhibited two yield points associated with the enhancement of the fluctuation and the generation and enhancement of voids on a stress-strain curve. On the other hand, the enhancement and generation and enhancement of voids occurred simultaneously in the HDPE, so the HDPE exhibited one yield point. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G23.00010: Equilibrium and non-equilibrium dynamics of polymers confined in nanopores George Floudas, Panagiotis Kardasis, Chien-Hua Tu Polymers confined in nanopores are away from equilibrium in a temperature range above the glass temperature. The nonequilibrium dynamics of linear and star-shaped cis-1,4 polyisoprenes confined within nanoporous alumina was explored as a function of pore size, d, molar mass and functionality. Two thermal protocols were tested; one resembling a quasi-static process (I), and another involving fast cooling followed by annealing (II). 2 Both thermal protocols establish the existence of a critical temperature below which nonequilibrium effects set-in. The non-equilibrium phenomena in pores reflects the nonequilibrium configurations of the adsorbed layer that extent away from the pore walls. The equilibrium times depend strongly on temperature, pore size and functionality. Subsequently, we studied the adsorption kinetics of PI by following the evolution of the dielectrically active longest normal mode with in situ nanodielectric spectroscopy. The extremely slow kinetics reflect the fact that exchanging chains with the pore surface have to pass through several unfavorable configurations (e.g trains, loops). The molar mass dependence of the characteristic adsorption times was in good agreement with a scaling theory proposed by de Gennes and later refined by Semenov and Joanny. Polymer electrolytes in the same nanopores also show slow equilibration times and their origin can be traced to chain adsorption. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G23.00011: Isolating the Impact of Reduced Domain Size on the Local Glass Transition Tg(z) Profile in PS/PnBMA Bilayers Alexander Couturier, Connie B Roth Dynamical gradients have long been observed in confined polymer systems where interfacial effects perturb the local dynamics and propagate into the material. The range of the dynamical gradient varies for different interfaces, where broader polymer-polymer interfaces can perturb dynamics across particularly long length scales spanning hundreds of nanometers. A major open question associated with understanding these dynamical gradients is how a finite domain size alters its range. To isolate the impact of only the reduced domain size without confounding effects from any additional interfacial perturbations, we focus on a bilayer film of polystyrene (PS) capped with poly(n-butyl methacrylate) (PnBMA), where the underlying silica substrate is neutral to PS. Fluorescence is used to measure the local glass transition temperature Tg(z) profile arising from the PS/PnBMA interfacial perturbation as the PS layer thickness is reduced. We find that the Tg(z) profile across a 75 nm PS layer capped with PnBMA is significantly shortened compared to the dynamical gradient previously observed across the unconstrained PS/PnBMA system. We demonstrate that constraining the dynamical gradient alters both the shape of the Tg(z) profile, as well as the local dynamical perturbation at the interfaces. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G23.00012: Driving Ionomers Towards Equilibrium: Neutron Spin Echo and Simulations Insight Chathurika J Kosgallana, Sidath I Wijesinghe, Manjula P Senanayake, Supun S Mohottalalage, Piotr A Zolnierczuk, Gary S Grest, Dvora Perahia From a single molecule to melts, clustering of ionomers drives the formation of far from equilibrium structures. With premise that cluster cohesion controls the path towards equilibrium, our study probes ionic clustering and follows the corresponding impact on the polymer dynamics using neutron spin echo and molecular dynamics simulations. Solutions of 10 Wt% polystyrene sulfonate in toluene, above the overlap concentration are studied as the ionic clusters are perturbed via addition of ethanol. Experimental and computational results for the dynamic structure factor S(q,t), are in excellent agreement. The dynamic data are then correlated with characteristics of ionic clusters attained from the simulations. In toluene, where well defined clusters are formed, the polymer motion is constrained, however below the inter cluster distance motion persists. Though the system contains significant amount of solvent, it is macroscopically locked. Perturbing the clusters through ethanol addition, the clusters are slightly perturbed but sufficient to remove the constraints. These constraint release without fully breaking the clusters impacts the macroscopic dynamics leading towards a shorter path towards equilibrium. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G23.00013: The effect of the density fluctuations of amorphous polymer on the plastic region Daisuke Iwahara, Shotaro Nishitsuji, Mikihito Takenaka, Masaru Ishikawa, Takashi Inoue, Hiroshi Ito It is generally known that amorphous polymers fracture with forming of the plastic region such as a crazing and shear yielding. To establish the fracture mechanism of amorphous polymer, it is very important to clarify how the plastic region was formed by deformation. Previous studies have been reported that forming plastic zone of Polycarbonate (PC) was influenced by amplifying the density fluctuations due to annealing below Tg. However, it is not clarified the relationship the density fluctuation and forming the plastic zone of Polymethylmethacrylate (PMMA) and Polystyrene (PS) with different fracture mode for PC. The purpose pf the study is to investigate how the change of the density fluctuations affect their plastic region. First, it was found that the plastic region obtained by polarized optical micrograph was different with the different fracture mode. Next, SAXS results show that the density fluctuations exist in PMMA and PS and its amplitude depend on each amorphous polymer. In addition, it was found that the density fluctuations induced by deformation, in case of PC and PMMA, while the fluctuations of PS did not change by deformation and appeared streak due to formed craze at just before at a break. |
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