Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R49: Polymer and Polyelectrolyte Rheology I: Molecular Sequence and ArchitectureFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY DBIO DFD GSNP Chair: Samanvaya Srivastava, University of California, Los Angeles Room: BCEC 252A |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R49.00001: Elasticity of Self-Assembled Block Copolymers in Water and Oil Mixtures Sahar Qavi, Millicent Firestone, Reza Foudazi Amphiphilic block copolymers self-assemble at water/oil interface and form different mesomorphic structures such as lamellar, micellar cubic, normal hexagonal and reverse hexagonal. Usually, these structures are polycrystalline and their elasticity depends on the orientation of their constituent’s single crystals. We provide a model to predict the elasticity and yielding of mesophases from their characteristic length and intermicellar interactions. Shear modulus of each structure has been calculated as a function of deformation (strain) applied in one direction. Zero shear modulus, G0, depends on the inverse of intermicellar distance with a power-law model. The power-law index for each structure is about n+2 where n is the degree of confinement in mesophase. Rheological properties of different mesophases of Pluronic P84 in the presence of water and p-xylene are used as case study. Our model is in good agreement with experimental data in the linear viscoelastic region. However, the yield strain value of experimental data is slightly lower than that of the model. Frequency sweep measurements were done to further characterize each mesophase structure and cooperative model was used to fit the frequency sweep data of mesopahses. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R49.00002: Exploring dynamics of polymerlike wormlike micelles in high shear flow Paul Salipante, Alex Conte, Vishnu Dharmaraj, Steven Hudson Wormlike micelle solutions entangle and flow like polymers, yet micelles can break and reform. Stress may influence breakage dynamics and the microscopic behavior of these fluids at high stress is not understood. We explore this behavior in pressure-driven microchannel flow. Velocity profiles are measured with high resolution using holographic 3D microparticle tracking velocimetry, to determine the relationship of stress and shear rate. As reported by others, this relationship depends on wall stress and channel dimensions and suggests diffusive processes whose rate depends on channel dimension. We therefore are measuring the local solution concentration with fluorescence microscopy, to explore molecular diffusion. We compare our velocity and concentration profiles to theoretical models that include a diffusive term in the stress balance, which becomes relevant at small channel dimensions. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R49.00003: Brownian Dynamics Simulations of Polyrotaxanes Phillip Rauscher, Stuart J Rowan, Juan De Pablo There is great interest in understanding how non-equilibrium dynamics are influenced by polymer topology, particularly in knotted and mechanically interlocking polymers (MIPs), which can occur naturally or be created synthetically. Polyrotaxanes are one such MIP in which cyclic molecules (“macrocycles”) are threaded onto a linear polymer backbone with large capping groups preventing disassembly. Materials derived from polyrotaxanes can possess unusual viscoelastic responses, which may be explained by the configurational entropy of the macrocycles along the backbone. This suggests that the number and distribution of macrocycles within a polyrotaxane can be leveraged to control the rheological properties. Here, we investigate this hypothesis using Brownian dynamics simulations of various polyrotaxane architectures in several different flow conditions, demonstrating how the distribution of macrocycles impacts the resulting structural and dynamical properties. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R49.00004: Topological glass in self-entangled ring polymers Beatrice Soh, Alexander Klotz, Rae Robertson-Anderson, Patrick Doyle The dynamics of entangled linear polymers is well understood in terms of the tube model. A remaining challenge in polymer physics is to fully understand the dynamics of ring polymers, which have no chain ends and lie outside the framework of the tube model. In this work, we perform single-molecule DNA experiments to investigate the dynamics of self-entangled ring polymers. We use electric fields to induce self-entanglements in circular DNA molecules, which serve as a minimal system for studying chain entanglement. Our experimental results show that self-threadings give rise to entanglements in ring polymers and can slow down polymer dynamics significantly. We find that strongly entangled circular molecules remain kinetically arrested in a compact state for very long times, thereby providing experimental evidence for a topological glass in ring polymers. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R49.00005: From Polyelectrolyte Complex Solution to Electrospun Fibers mor Boas, Gleb Vasilyev, Arkadii Arinstein, Eyal Zussman Mixing semi-dilute solutions of highly charged oppositely polyelectrolytes (PEs) generally yields compositions spanning complexes (solid) to coacervates (elastic liquid) to dissolved solutions with increasing salt concentration. In case one of the PEs is weakly charged, the PE pair can be dissolved without salt by adding an organic co-solvent. Such a system was recently studied with 1:1 (by monomer ratio) poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) dissolved in a mixture of water/ethanol. Rheological investigation of semi-dilute solution demonstrated maximal relative viscosity at 40% ethanol. The PECs in aqueous medium was opaque but at 40% ethanol solution was transparent. Extensive stretching and confining this solution by electrospinning results in 300-600 nm fibers. Polarized FTIR demonstrates preferred macromolecular orientation along the fiber axis which implies a better packing of macromolecules due to their orientation along the fibers. The fibers demonstrate pH-responsive behavior with 17% ionization degree and an increase in fiber diameter of 600% in a gel-like structure at low pH. At neutral pH, the ionization degree is at least 79% and deswelling is observed, demonstrating high fiber stiffness (increased by 104) with minimal water consumption. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R49.00006: Solution Rheology of Polyelectrolyte-Grafted Nanoparticles Chongfeng Zhang, Pinar Akcora The variations in hydrodynamic sizes of a series of poly(acrylic acid) (PAA)-grafted silica (SiO2) nanoparticles indicated the compressed and fully extended grafted chain conformations as pH increased. At semi-dilute concentrations, interactions between grafted-chains were investigated by measuring the complex viscosity of the solutions. We found that the viscosity of grafted particle solution increased by an order of magnitude as a result of hydrogen bonding between inter-particles at neutral pH; and decreased by two orders of magnitude at the higher pH due to strong electrostatic repulsion between grafted chains. In particles with the higher graft density, the change in viscosity was reduced but followed the similar trend as pH was varied. The PAA-grafted particles were found to form hydrogen-bonded networks with the addition of short poly(vinyl pyrrolidone) (PVP) chains. The viscosity adjustment by the PVP concentration suggested that hydrogen bonding was possible within the grafted chains of individual particles at low graft density, whereas networking between inter-chains occurred with the high graft density. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R49.00007: ABSTRACT WITHDRAWN
|
Thursday, March 7, 2019 9:24AM - 9:36AM |
R49.00008: Effect of edge disturbance on shear banding in polymeric solutions Seunghwan Shin, Kevin Dorfman, Xiang Cheng Edge-induced instabilities have been suggested as one of the possible causes of experimentally observed shear-banding in well-entangled polymer solutions/melts. Using a high-aspect-ratio planar-Couette shear cell, we study the penetration length (L) of edge disturbance and the development of bulk shear profiles in highly entangled DNA solutions by measuring shear profiles while varying the locations from near-edge to center of the shearing plates. Under a weak oscillatory shear flow, where the corresponding Weissenberg number (Wi) > 1 and the DNA solutions display linear shear profiles with strong wall-slip, we find that L is comparable to the gap (H) between the plates. On contrary, under a stronger oscillatory shear (Wi > 1) that produces shear-banding profiles, L is an order-of-magnitude larger than H and the region of the stabilized shear-banding profiles becomes anisotropic. Moreover, a well-developed shear-banding profile persists farther away from the edge, where the edge effect is negligible, which implies its true bulk nature. Our results clarify a surprisingly long penetration of the edge disturbance and the bulk nature of shear-banding flows in entangled polymeric solutions under large amplitude oscillatory shear. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R49.00009: Viscoelastic Response of Branched Polyethylene Combs: A Molecular Dynamics (MD) Simulation Study Sidath Wijesinghe, Dvora Perahia, Gary Grest Polymers exhibit distinctive rheological behavior depending on their architecture. Addition of small number of branches is sufficient to affect the rheology of polymers compared to their linear counterpart with the same molecular weight. Here, using coarse grained molecular dynamics simulations we resolve the effects of the branch length and branch density on the viscoelastic response of entangled polyethylene (PE) melts with branch lengths above and below the entanglement length. The stress relaxation behavior is measured following a small perturbation and from the stress autocorrelation function using the Green-Kubo relation. We find that the plateau modulus is sensitive to both branch length and branch density and decreases with decreasing branch length, consistent with reduction in entanglement length and increase in tube diameter. This study contributes to the nanometer level insight into long-lived problems in viscoelastic responses of polymers. |
Thursday, March 7, 2019 9:48AM - 10:24AM |
R49.00010: Flow behavior and impact of shear fields on structural transitions in diblock and triblock copolymer aqueous solutions Invited Speaker: Lynn Walker Low molecular weight diblock and triblock polymers in selective solvents form disordered micellar phases at low concentration and liquid crystal phases at high concentration (or low solvent to amphiphile molar ratio in the case of water). The energetic barriers between different lyotropic states and structures are large enough for systems to become kinetically trapped, but low enough for weak external fields to alter the nanoscale structure. We have been able to align ordered structures and anneal out defect texture in polycrystalline materials. Results for two different block copolymers in aqueous solution will be shown and rheological features correlated with structural measurements (through SANS and SAXS). The use of weak shear fields to align lyotropic structures and then transition to other low and high symmetry structures will be demonstrated. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R49.00011: Accelerated diffusion and entanglement evolution during relaxation of aligned polymer melts Marco Galvani, Austin Hopkins, Thomas O'Connor, Mark Owen Robbins The dynamics of entanglement formation and loss has long been recognized as a fundamental mechanism behind the macroscopic rheological properties of polymer melts. Models based on entanglements and a confining tube have been very successful in describing equilibrium diffusion and low rate viscous flow, but it is not yet clear how to extend these tube models to highly aligned states produced by shear or elongational flow and experiments cannot directly measure entanglements. Here we use molecular dynamics simulations to follow the motion of monomers and chains and the evolution of entanglements during relaxation from highly aligned states produced by shear and elongational flow. Polymers are modeled with the coarse-grained FENE potential with varying chain stiffness and entanglements are followed with both Primitive-Path Analysis and the Z1 code. Chain retraction occurs over the equilibrium Rouse time and chains reorient on the equilibrium disentanglement time. In sharp contrast to existing theories, the entanglement density does not decrease during chain retraction. A monotonic increase in entanglement density is observed that can be understood from the chain dynamics. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R49.00012: Filled Rubbers Missing High Harmonics in LAOS Shan Jiang, Xiaorong Wang In the present work, the rheological properties of a number of filled elastomers under large amplitude oscillatory shear conditions are investigated. In the nonlinear regime the stress outputs of filled rubbers are surprisingly sinusoidal and essentially absent of any high harmonics. Fourier transform analysis shows that the ratio of the third to the first harmonic responses (I3/I1) in the range when G’ loses 70% of its original value and G” passes through its maximum is typically less than 4%. As the strain amplitude increases the ratio I3/I1 also displays a maximum and can be linearly corrected with the damping factor tanδ. Such a relationship is independent of the filler content and may reveal some important fundamentals behind this phenomenon. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R49.00013: The positions and trajectories of deformed polymers and networks Kaikai Zheng, Yifan Zhang, Lingxiang Jiang, Jiang Zhao, Steve Granick This laboratory is interested to understand the heterogeneity that underpins an overall rheological response. To this end, we are integrating fluorescence and phosphorescence imaging with controlled rheological polymer deformations. Integrating epifluorescence imaging with a rheometer, we image individual molecules. Integrating new mechanophores with polymerized networks, we image individual stressed chains. Integrating polymer deformation with a newly-designed approach for fast STED (super-resolution) imaging, we also go below diffraction limitations. Result findings will be discussed. |
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