Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C51: Recent Developments in Nonequilibrium Dynamics and Rheology of Entangled Polymer LiquidsInvited
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Sponsoring Units: DPOLY Chair: Shiqing Wang, Univ of Akron Room: BCEC 253A |
Monday, March 4, 2019 2:30PM - 3:06PM |
C51.00001: Molecular Rheology of Entangled Polymeric Fluids: New Discoveries and Remaining Challenges Invited Speaker: Bamin Khomami Quantitative understanding of the influence of environmental variables on the dynamic evolution of microstructure in polymeric fluids plays a central role in soft matter physics as well as the processing of a wide variety of soft materials. Atomistic simulation via non-equilibrium molecular dynamics (NEMD) offer a viable alternative to experiment wherein the dynamics of individual macromolecules can be tracked independently, thus allowing for relevant calculations of their single-chain configurational properties as well as bulk-average properties, which in turn allows detailed examination of the fundamental tenants of reputation/ tube based theories for flow of entangled polymeric fluids. |
Monday, March 4, 2019 3:06PM - 3:42PM |
C51.00002: Rheological behavior of entangled polymer melts and solutions in fast extensional flow Invited Speaker: Qian Huang Extensional rheology of polymer liquids is highly sensitive to molecular architecture. Accurate and reliable stress-strain measurements of extensional flow play a crucial role in understanding the nonlinear rheological properties of polymers. However, extensional flow is difficult to measure reliably. |
Monday, March 4, 2019 3:42PM - 4:18PM |
C51.00003: Forced-Based Microscopic Theories of the Equilibrium Dynamics and Nonlinear Rheology of Entangled Rod and Chain Polymer Liquids Invited Speaker: Kenneth Schweizer Using ideas from microscopic glass physics, force-based statistical mechanical theories for the transverse tube confinement field of liquids of zero-excluded-volume rods (needles) and chains have been constructed based solely on dynamic uncrossability which is exactly enforced at the two body level. Coils are coarse grained to chains of self-consistently-determined primitive-path steps. Tube localization emerges above a universal critical degree of interpenetration, and the melt tube diameter scales with packing length. Importantly, the confinement field is anharmonic, softening for large transverse displacements, corresponding to a finite maximum entanglement force. The predicted form of the confinement field is in excellent agreement with f-actin solution experiments and chain melt simulations. The tube field softens with orientation, hardens for affinely stretched chains, and is potentially destroyed beyond a critical stress (microscopic yielding). Nonequilibrium theories and simple constitutive equations under continuous startup shear have been constructed. For chain melts, new physical aspects include a dynamic tension blob scaling construction of a grip force that is the microscopic origin of stretching, a force imbalance criterion for termination of affine deformation and onset of retraction, the influence of entanglement length heterogeneity, an emergent form of convective constraint release, and rate-accelerated retraction of strongly stretched chains. For fast deformations we predict novel fractional power law scalings with rate for the stress overshoot and undershoot, steady state total and orientational stress and contour length stretch, a universal master curve in the elastic-viscous crossover regime, and strong connections between the overshoot and steady state. No adjustable parameter numerical predictions are quantitatively compared with multiple experiments and simulations. This work was done in collaboration with Shi-Jie Xie and Daniel Sussman. |
Monday, March 4, 2019 4:18PM - 4:54PM |
C51.00004: Fingerprinting Molecular Relaxation in Deformed Polymers Invited Speaker: Yangyang Wang A central problem in polymer rheology is to understand how the intra- and interchain configurations are transformed by the macroscopic deformation. The rheo-small-angle-neutron-scattering (rheo-SANS) technique has long held the promise of offering a molecular perspective on this issue. However, despite decades of development, the full potential of this experimental technique is yet to be realized. By combining and extending several key concepts in the literature and drawing upon the so-called spherical harmonic expansion technique, here we describe a new framework [Phys. Rev. X 7, 031003 (2017); Phys. Rev. Lett. 121, 117801 (2018)] for connecting the SANS experiments and the molecular rheology of polymeric liquids. We show how several two-point spatial correlation functions, such as the anisotropic single-chain structure factor and pair distribution function, can serve as a bridge between rheo-SANS experiments on the one hand and theoretical studies on the other, providing a convenient platform for molecular rheology of polymers. To demonstrate the power of this idea, we will discuss in this talk our recent SANS experiments on deformed homopolymer melts as well as polymer blends. |
Monday, March 4, 2019 4:54PM - 5:30PM |
C51.00005: Shear banding in semidilute polymeric solutions: Experiments and modeling Invited Speaker: Natalie Germann Shear banding is the formation of localized velocity bands with different shear rates, and is observed in semidilute polymer solutions and other soft materials. DNA solutions are convenient model systems owing to their characterization in standard rheometric geometries without edge fracture. Furthermore, their wall slip can be minimized by using glycerol as a solvent. In this talk, we focus on the investigation of shear banding of 13 mg/ml of 115 kbp double-stranded DNA (dsDNA) and 11 mg/ml of 50 kb single-stranded DNA (ssDNA) in glycerol/aqueous buffer solutions and compare the results with our recent works on polyacralymide and polyethylene oxide. The frequency sweep of dsDNA corresponds to that of a soft gel with a small dependence at intermediate frequencies. On the other hand, the behavior of ssDNA is comparable to that of a dense micellar solution having a unique local minimum related to micellar breakage. Due to the much smaller persistence length, ssDNA is more flexible and easily creates small structural units most likely in association with glycerol. The strain sweep of dsDNA is strain thinning and the shear bands are mainly strain-dependent. Early strain stiffening with weak bands is observed for ssDNA followed by a terminal flow regime of the collapsed structure. To summarize our recent activities on shear banding, we will briefly discuss here our mesocopic modeling and simulation efforts in mixed flows (e.g., 4:1 contraction, die extrusion). |
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