Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F35: Biopolymer Structures and AssembliesFocus
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Sponsoring Units: DPOLY DSOFT Chair: John Dorgan, Michigan State Univ Room: 507 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F35.00001: BREAK
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Tuesday, March 3, 2020 8:36AM - 8:48AM |
F35.00002: From Modeling Free Chains with the Rosenbluth Algorithm to Modeling Rigid, Compact, and Overlapped Chains with Our Developed Algorithm Ebtisam Aldaais, Scott Russell Crittenden In 1955, Rosenbluth developed a chain-growth technique for Self-Avoiding Random Walk (SARW) with a set of weights that allows one to approximate all possible configurations of a real chain in a cubic or square lattice. We incorporate the Boltzmann factors for intermolecular bending energy into the monomer growth direction choice in the Rosenbluth algorithm to model chains of arbitrary nearest-neighbor rigidity. This allows for the consideration of compact, free, or extended chains. We validate against, and compare to, various other results, showing very good agreement with known results for short chains and demonstrate the ability to model chains up to 500 segments long, far beyond the length at which the normal Rosenbluth method becomes unstable for reasonable non-zero bending energies. Furthermore, we incorporate the Boltzmann factors for finite overlap energy to model chains that allow only two segments to overlap, Single-Overlapped Random Walk (SORW), into our algorithm. Again, we validate our results with a complete set of SORW for short chains. Our developed algorithms can be easily modified to model any configuration, stiff, free, compact, or overlapped, of polymer-like molecules in biological and non-biological systems. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F35.00003: Simulations of Grafted Methylcellulose Chains in Solution Vaidyanathan Sethuraman, Kevin D Dorfman Recent experiments on methylcellulose chain grafted with polyethylene glycol in solution showed inhibition in methylcellulose fibril formation at high grafting density. We utilize coarse-grained molecular dynamics simulations to understand the influence of grafting on methylcellulose chains. The interaction between the grafts and the methylcellulose chains, as well as the grafting density, are systematically varied. Single chain simulations show that the precursor toroidal structure responsible for fibril formation is hampered by the graft, while Multi chain simulations show that the distance between the centers of masses of the chains increase beyond the minimum capture radius required for fibril formation at high grafting densities. We further demonstrate that conformational fluctuations are suppressed with increasing grafting density. Together, our results support the suppression in fibril formation in grafted methylcellulose systems. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F35.00004: Random Copolymer Complexation with Proteins and Possible Applications Jeremy Wang, Baofu Qiao, Trung Nguyen, John Torkelson, Monica Olvera De La Cruz Random copolymers are polymers made of two more or monomer components, with their properties determined by the statistical distribution of the monomer sequence. Generally, these properties are understood to be averages of the different components, but recent work from the Olvera de la Cruz group has shown that the statistical distribution of random copolymers make them uniquely suited to form complexes with proteins, which have a heterogenous surface composed of hydrophilic, hydrophobic, and charged domains. This discovery allows us to develop novel and cost-effective techniques to enhance the properties of certain proteins, such as those with enzymatic functions, and increase their stability in demanding environments. The basic principles and potential applications of such techniques will be discussed. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F35.00005: Synthesis and Self-assembly of Saccharide-Polystyrene Hybrid Block Copolymers Minji Seo, Sheng Li Oligosaccharide based block copolymers are a new class of hybrid polymers containing both natural and synthetic segments. Due to the large segregation strength between the hydrophilic saccharide block and the hydrophobic synthetic block, the resulting block copolymers are expected to microphase separate at small molecular weights, yielding ordered morphologies with sub-10nm feature sizes. In this contribution, a series of saccharide-containing diblocks and triblocks were prepared by combining maltotriose with polystyrene of different chain lengths. The polymer conjugates were synthesized via copper(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition of alkyne-functionalized maltotriose and azido-functionalized polystyrene. Additionally, bifunctional initiators were used to prepare triblocks of polystyrene center block and maltotriose end blocks. Despite the small size of maltotriose, the resulting block copolymers were found to microphase separate to form well-ordered microdomain structures. Their bulk morphologies as well as order-disorder transition behavior were examined to illustrate the complex phase behavior of these hybrid materials. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F35.00006: Polyvinyl alcohol composite hydrogels containing mixtures of cellulose nanocrystals and chitin nanofibers Cameron Irvin, Chinmay Satam, Paul Russo, James Carson Meredith, Meisha Shofner Among bio-based polymers, cellulose and chitin are abundant and available in a variety of forms, including nanofibers. Due to their anticipated mechanical properties and anisotropic structure, nanofibers of cellulose and chitin are desirable reinforcing fillers in polymers. These nanofibers are also dispersible in water, making them desirable as reinforcing fillers in polymer hydrogels as well. In this work, we have examined how cellulose nanocrystals (CNCs) and chitin nanofibers (ChNFs) may be used separately and as mixtures to affect the properties of poly(vinyl alcohol) (PVA) hydrogels. CNCs and ChNFs have negative and positive surface charges, respectively, providing opportunities for bonding between the nanofibers when used as mixtures and modifying the hydrogel properties further. The results of this work suggested that the types of networks formed were different with different filler types and these differences were observed through swelling behavior of the hydrogels and mechanical properties. Overall, these results demonstrate that nanoparticle mixtures may be used as effective reinforcements for polymer nanocomposites when compatible surface interactions are present between all the components. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F35.00007: Hierarchically Organized Structure of Electrospun Nanofibers from Computationally Designed Peptide Bundlemers Kyunghee Kim, Christopher J. Kloxin, Jeffery G Saven, Darrin John Pochan Fiber materials made from natural or synthetic polymers can be used as high performance materials exhibiting high stiffness, strength, and/or elongation, all while being light weight. The ability to create a desired internal nanostructure with controllable molecular interactions in the fibers is paramount to a construction of new materials with unique structural features and a remarkable combination of high stiffness, strength, and elongation. Herein, peptides are computationally designed to self-assemble into coiled coil bundles that serve as supramolecular monomers, or “bundlemers”, to create a hierarchical structure for high performance nanofibers. The bundlemers have chemical functionality for desired covalent interactions between bundles to facilitate hierarchical chain growth that displays rigid-rod character. The rigid rods are employed to fabricate uniform nanofibers via electrospinning. The rod chains are observed to be aligned along the fiber axis due to their molecular rigidity and the solution flow during electrospinning process, which impacts the eventual mechanical properties of the nanofibers. The mechanical properties of electrospun rod fibers are investigated as a function of rod length and intra- or inter-chain interactions in the rod chains. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F35.00008: Chitin Nanocrystals confined to polymer microgels. Sujin Lee, Elsa Reichmanis, Jung O Park, Mohan Srinivasarao Chitin is the second most abundant polysaccharide after cellulose, which can be extracted from exoskeletons of crustaceans and also from cell walls of fungi and insects. Similar to cellulose nanocrystals, chitin nanocrystals can be isolated through acid hydrolysis and form cholesteric phase. We investigate chitin nanocrystals confined to pnipam microgels using microfluidics device. The twisted structure of chitin nanocrystals are preserved within the polymer spheres, as characterized by optical microscopy. The droplet radius, R of the microgels can be adjusted by changing the volumetric flow rate of oil phase in a microfluidics device. Interestingly, the fabricated microgels shows bipolar structure with the shape of prolate spheroids. They exhibit swelling-deswelling behavior upon temperature change along the axis of helix. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F35.00009: Enhanced mechanical properties of fatty acid-derived thermoplastic elastomers through incorporation of ionic interactions Megan Robertson, Wenyue Ding, Josiah Hanson Vegetable oils and their fatty acids are attractive resources for polymers, due to their worldwide abundance, yet the presence of long alkyl chains greatly impacts the resulting polymer properties. The incorporation of ionic interactions in the unentangled poly(n-alkyl methacrylate) midblock of a fatty acid-based thermoplastic elastomeric triblock copolymer was explored as a method of improving its mechanical properties. Poly(methyl methacrylate-b-(lauryl methacrylate-co-tert-butyl methacrylate)-b-methyl methacrylate), which exhibits low tensile strength and elongation at break, was modified by hydrolysis to form poly(methyl methacrylate-b-(lauryl methacrylate-co-methacrylic acid)-b-methyl methacrylate). The methacrylic acid group in the midblock was further neutralized with sodium hydroxide to introduce ionic crosslinks into the system. Increased relaxation time was observed by increasing ion and acid contents. The triblock copolymer mechanical properties were improved significantly by the incorporation of ionic interactions. Enhancement of mechanical properties was correlated with the relaxation time of the midblock. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F35.00010: Characterizing Network Structure in Lignin-Based Hydrogel Composites for Aqueous Separations Nicholas Gregorich, Junhuan Ding, Mark C. Thies, Eric M Davis Lignin-based hydrogels have garnered attention for use in a variety of aqueous separations as lignin is a sustainable, naturally abundant biopolymer with a high concentration of hydroxyl groups, which can be utilized as crosslinking sites during hydrogel fabrication. However, to date, widespread use of these materials is hindered by our limited understanding of how the addition of lignin alters the network structure of these composite hydrogels. Herein, lignin–poly(vinyl alcohol) (PVA) composites were synthesized using lignins of prescribed molecular weights (MWs) and low dispersity using two different crosslinking agents (CLA) – ammonium persulfate and glutaraldehyde . The permeability of various pollutants through the hydrated composites was measured via ultraviolet-visible spectroscopy, where penetrant permeability was found to depend on the MW of lignin and PVA, as well as the concentration of CLA utilized during membrane fabrication. In addition, poroelastic relaxation indentation was used to characterize both the mechanical and transport properties of the composites. Results from this work indicate that transport of pollutants through the composite hydrogels is governed by a combination of the network structure and strength of interaction between the pollutant and lignin. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F35.00011: Gelation and fibril formation of poly(N-isopropylacrylamide)-grafted methylcellulose McKenzie Coughlin, Jerrick Edmund, S. Piril Ertem, Svetlana Morozova, Peter Schmidt, Theresa M Reineke, Frank S Bates, Timothy Lodge Methylcellulose (MC) is a commercially relevant cellulose ether. As a water-soluble polymer, MC is used in a variety of applications from food to construction materials. Many applications exploit the thermoreversible gelation of MC at ca. 60 °C, which has been correlated with the formation of nanofibrils upon heating. Previously, we have shown that grafting poly(ethylene glycol) (PEG) chains onto MC modifies the fibril structure, including suppression of fibrils at high enough grafting densities. To expand our understanding of fibril formation, we have grafted poly(N-isopropylacrylamide) (PNIPAm) onto MC at various grafting densities. PNIPAm is water-soluble at room temperature, however, it displays a lower critical solution temperature at ca. 32 °C and phase separates upon heating. The chain conformation of PNIPAm-grafted MC was studied using dynamic and static light scattering as a function of temperature and grafting density. Cryogenic electron microscopy and small-angle X-ray scattering revealed changes in fibril structure and formation. Utilizing small-amplitude oscillatory shear, we characterized the change in modulus and gelation behavior. The effects of PNIPAm-grafting on MC gelation and fibril formation will be compared to the results obtained with PEG-grafted MC. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F35.00012: Anamolous Hyperpolarization observed in polyacrylate gels and their implications on polyelectrolyte theory Susan Kozawa, Anne Walker, Jonah Scott-McKean, Jeanette Garr, Chris Flask, Michael Hore, Alberto Costa, Gary Wnek <script id="th-iframe-script" src="chrome-extension://ofdopmlmgifpfkijadehmhjccbefaeec/assets/comms/commsiframe.js"></script>Poly(acrylate) gels have been shown to exhibit electrical potentials in the range normally afforded by living cells. We have unexpectedly found that bathing poly(acrylate) gels in aqueous solutions of monovalent salts such as KH2PO4 in a narrow concentration range (ca. 8-16 mM) leads to a softening of gels without measurable volume changes. Moreover, electrical potentials of the gels in KH2PO4 solutions show an abrupt increase in gel potential concomitant with the mechanical softening transition. Magnetic resonance imaging experiments reveal an increase in water spin-spin relaxation time (T2) at this range and small angle neutron scattering demonstratse a structural change at this transition, indicating increased water mobility due to a change in mesh size. This leads us to suggest additional considerations toward a more comprehensive theory of polyelectrolytes, namely ion site and affinity. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F35.00013: Strain-Field Analysis of Subsonic and Supersonic Cracks in Filled Elastomers Thanh-Tam Mai, Kenji Urayama In the present study, the transition in the characteristics of local crack-tip strain-field from the subsonic (V/Cs < 1) to supersonic (V/Cs > 1) cracks in filled elastomers is investigated, where V and Cs are crack-growth velocity and shear wave speed, respectively. The crack propagation of the specimens stretched by pure shear deformation is observed by a digital high-speed camera. The crack-tip strain-field is evaluated by the two-dimensional digital image correlation technique (DIC) on the basis of the captured speckle images. The critical behavior of the vertical strain field (eyy) near the crack-tip is characterized by the exponent α in the power law, eyy ~ (1/r)α, known as a crack-tip singularity field. The exponent α in the subsonic crack is constant and larger than those of the linear elastic fracture mechanics (LEFM, α = 0.5) as well as weakly nonlinear fracture mechanics (WNLM, α = 1). In contrast, the exponent α in supersonic crack significantly increases with an increase in the crack growth rate. |
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