Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S51: Dynamics and Rheology of Polyelectrolytes and BiopolymersInvited
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Sponsoring Units: DPOLY DBIO Chair: Vivek Sharma, University of Illinois at Chicago Room: BCEC 253A |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S51.00001: Nonlinear Elongational Rheology of Unentangled Polystyrene and Poly(p-tert-butyl styrene) Melts Invited Speaker: Hiroshi Watanabe Nonlinear rheology under uniaxial elongation was examined for unentangled melts of polystyrene (PS27; M = 27k, nK= 30) and poly(p-tert-butyl styrene) (PtBS53; M = 53k, nK= 35) having nearly the same number nK of Kuhn segments per chain. For both materials, the steady state elongational viscosity ηE exhibited hardening and then softening on an increase of the Weissenberg number Wi ≥ 0.3 (Wi = τκ, with τ and κ being the longest relaxation time and the Hencky strain rate). For these unentangled melts, the hardening was unequivocally related to the finite extensible nonlinear elasticity (FENE), and the softening, to suppression of the FENE effect due to reduction of the segmental friction ζ occurring for the highly stretched/oriented chain. Thus, the ζ-reduction, speculatively discussed for entangled melts, was experimentally confirmed for unentangled melts. The softening at high Wi was weaker for PtBS53 than for PS27 despite the similarity of their nK values, which suggested that the magnitude of ζ-reduction depends on the chemical structure of the chain. Further details of this ζ-reduction, analyzed with the aid of the FENE bead-spring model modified for the ζ-reduction, are discussed in relation to the local motion of the chain necessary for adjusting ζ. |
Thursday, March 7, 2019 11:51AM - 12:27PM |
S51.00002: Salt-induced polyelectrolyte capsule formation in microfluidics Invited Speaker: Joao Cabral Microfluidics provides an exceptional platform for the generation of polymer solution droplets and their subsequent manipulation. We describe the formation of carboxymethyl cellulose (CMC) particles and capsules induced by salt diffusion. Generally used as a sodium salt, NaCMC is an anionic, weak, semiflexible polyelectrolyte, and one of the most widely used polyelectrolyte cellulose derivatives, with applications in the food, pharmaceutical, personal care, cosmetic, and paper industries. We employ SANS, light scattering, and rheology to probe the conformation and dynamics of aqueous NaCMC solutions across a wide range of molecular weight (Mw), degree of substitution, salt (mono, di and trivalent) and polymer concentrations. We then investigate the addition of a series of multivalent salts to induce the gelation and/or precipitation of bulk NaCMC solutions, which is spatiotemporally resolved by SANS and microscopy, establishing salt front propagation kinetics and accompanying conformational changes of the polymer. Equipped with this knowledge, we design and fabricate CMC gel capsules and particles with prescribed dimensions and external shape, microstructure and dissolution profile. |
Thursday, March 7, 2019 12:27PM - 1:03PM |
S51.00003: Topological Effects on Movements of Charged Macromolecules in Crowds Invited Speaker: Murugappan Muthukumar Charged macromolecules dispersed in aqueous media are ubiquitous since life began on Earth and continue to catalyze formulations of modern materials. A fundamental understanding of the rich phenomenology on movements of charged macromolecules in crowded environments continues to be elusive, due to the long-ranged nature of both the topological correlation from chain connectivity and electrostatic correlation from the charges in the system. Strong coupling among these long-ranged interactions results in a variety of rich behavior unparalleled in uncharged systems. We will present recent advances on the collective dynamics of charged macromolecules in solutions and hydrogels. In particular, the “ordinary-extraordinary” dynamics, single molecule translocation through a protein channel under coupled forces, and the newly discovered topologically frustrated non-diffusive dynamics of charged macromolecules inside charged hydrogels will be discussed. |
Thursday, March 7, 2019 1:03PM - 1:39PM |
S51.00004: How structural modifications of pectin affect its gelling and complexation behavior Invited Speaker: Ruth Cardinaels Pectin is a plant cell wall polysaccharide that is intrinsically present in many plant-based food products, both in the plant cell particles as well as in the serum phase. In addition, extra pectin is frequently added to food products as a gelling agent and source of dietary fibre. Pectin is a polyelectrolyte with a backbone of galacturonic acid units, organized in linear and branched domains. The detailed pectin structure can be very heterogeneous even within a single cell wall. The galacturonic acid units that originally contain methylester groups can undergo deesterification thereby leaving negatively charged acid groups. Depending on the processing steps that in general include thermal treatment as well as mechanical homogenisation, various degrees and patterns of methylesterification [1,2] as well as degrees of branching can result [3]. These structural features determine the rheological properties of pectin solutions [1] as well as their gelling propensity by viscoelastic network formation [2,3,4]. Moreover, in typical food products pectin is in contact with other polysaccharides and proteins, which can result in complex formation, aggregation or phase separation. The type of interaction, phase boundaries and resulting microstructure are strongly contingent on the structural features of pectin [5]. Here, effects of processing techniques that allow to tailor pectin’s structural features will be discussed along with the relationships between these structural features and pectin’s functional properties. |
Thursday, March 7, 2019 1:39PM - 2:15PM |
S51.00005: Network connectivity, viscoelasticity and failure in gel networks: microscopic insights into soft complexity. Invited Speaker: Emanuela Del Gado Gel networks assembled from polymers, biopolymers, small particles or aggregates can be stretched, flow, squeezed or fractured, but controlling and being able to design such processes (think of soft inks for 3D printing technologies) requires a fundamental understanding that is still lacking. We have developed a theoretical/computational approach that addresses in particular the role of the network topology in such materials, its stress-controlled evolution over time and its implications for the mechanics. I will give an overview of the novel insight gained into the origin of the uniquely wide-ranged viscoelastic spectra and the presence of a topologically controlled softness in gel networks. I will discuss how our findings can help understand the nontrivial mechanical response of soft gels in different contexts, further develop constitutive models, and design smart materials. |
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