Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z18: Biological and Charged PolymersFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Sibani Lisa Biswal, Rice University Room: McCormick Place W-184D |
Friday, March 18, 2022 11:30AM - 11:42AM |
Z18.00001: Efficient Removal of Microcystin Toxins in Contaminated Fresh Water by Biocompatible Polymer Complex Coacervates Manuela Ferreira, Yingxi Elaine Zhu Microcystins (MC) are one of the most commonly found cyanotoxins in the U.S. freshwater sources, which are released from the blue-green algae blooms into the surrounding water and harmful to human and animal health. The safe level of MC concentration in drinking water is regulated to be more than 1-1.6 μg/L, yet its concentration in natural freshwater could reach to up to 1800 μg/L, making it a hazard for consumption and daily uses. Among different toxin chemical structures (congeners) that are released during the algae blooms, microcystin-LR (MC-LR) is the most abundant and toxic. In this study, we demonstrate the exploration of spontaneous liquid-liquid separating polymer coacervation of biocompatible polyethylene oxide (PEO) and polyacrylic acid (PAA) via hydrogen bonding to rapidly and effectively remove MC-LR and other congeners from aqueous solutions. The efficiency of MC-LR removal strongly depends on the composition of PEO-PAA complex coacervates, where an optimal composition is defined. Moreover, gel-like PEO-PAA complexes could reach near 90-97% MC toxins, far exceeding the reported performance of polymer membrane separation or other methods. Such biocompatible polymer coacervates could be further developed into a safe and scalable treatment to remove harmful cyanotoxins for drinkable fresh water. |
Friday, March 18, 2022 11:42AM - 11:54AM |
Z18.00002: A comparison of experimental bacterial genome mapping data with results from simulation using a coarse-grained dsDNA construct Swarnadeep Seth, Arthur Rand, Walter W Reisner, Robert Sladek, William Dunbar, Aniket Bhattacharya We design in silico an experimental dual nanopore setup that mimics the original experiment performed by Nooma Bio Inc., to obtain insights into dynamics and conformation of the captured dsDNA at sub-nanometer length scales. We mimic “flossing" in silico using a coarse-grained model of a dsDNA with 2048 beads of diameter 8 nanometers (24 base pairs) that correspond to the experimental 48500 base pair λ-phage DNA with 15 motifs. The simulation results capture the nonequilibrium dynamics of flossing and enable us to make a one-to-one comparison of the dwell time distribution of the individual motifs and the genomic lengths between any two motifs. In addition, by varying the field bias and other controlling factors, we obtain physical insights for the entire translocation process. |
Friday, March 18, 2022 11:54AM - 12:06PM |
Z18.00003: Electron Transport Kinetics for Viologen Containing Polypeptides with Varying Side Group Linker Spacing Alexandra D Easley, Cheng-Han Li, Tan Nguyen, Shih-Guo Li, Miao Qi, Karen Wooley, Daniel Tabor, Jodie L Lutkenhaus Redox-active polymers (RAPs) such as macromolecular nitroxide radicals have been studied as electrode materials for organic batteries and electronics. However, there has been little work done to investigate the structure-electron transfer relationship for redox-active polymers swollen with battery electrolyte. In this talk, the electron transfer and performance of three viologen-based RAPs with varying linker spacing is considered using both computational and experimental methods. The polypeptide backbone is selected to introduce degradable functionalities into the polymer and enhance the recyclability. Computationally, the diffusion of the viologen group is determined from trajectory analysis for the three polymers and related to their experimentally observed charge-transport behavior. Experimentally, cyclic voltammetry and chronoamperometry were used to determine the rate of electron transfer. The capacity of the polypeptides is determined with a lithium metal half-cell battery to elucidate the linker effect on the relationship between electron transfer rates and capacity. |
Friday, March 18, 2022 12:06PM - 12:18PM |
Z18.00004: Single-sequence protein structure prediction using language models and deep learning Nazim Bouatta |
Friday, March 18, 2022 12:18PM - 12:30PM |
Z18.00005: Probing Preferred Orientation in Cellulosic Materials: Nanocrystals, Wood, and Beyond Yimin Mao, Xin Zhang, Robert M Briber Preferred orientation is an inherent property of cellulose in its native biological form and has been an inspiration for material scientists. We demonstrate how to use different scattering techniques, including small- and wide-angle neutron and X-ray scattering, to understand preferred orientation of cellulosic materials at multiple length scales. Cellulose nanocrystals (CNC) can be produced by disintegrating microfibers in plant cell walls using sulfuric acid hydrolysis, which exhibit nematic liquid crystal phase behavior. Owing to the enhancement of the total magnetic moment in the self-assembled nanocrystal stacks, CNC particles can be aligned by weak magnetic fields (~0.5 T) in the nematic phase, and be characterized by using small-angle neutron scattering (SANS). SANS was also used as a non-invasive probe to quantify cross-sectional size of microfibrils in wood, taking advantage of the dramatic difference in scattering length density between deuterated water and hydrogenous cellulose chains. The oriented fibril crystals serve as an excellent bio-template that can incorporate transition metal ions to form an coordinated open framework. Modeling such complex structures using fiber X-ray diffraction is discussed. |
Friday, March 18, 2022 12:30PM - 12:42PM Withdrawn |
Z18.00006: Associating polymer features of native cellulose in ionic liquid solutions Ralph H Colby, Daniele Parisi, Nyalaliska Utomo, Ravisara Wattana, Joshua E Bostwick Cellulose is the most abundant bio-based polymer natural resource on Earth today. Certain ionic liquids (IL) have been discovered to be the best solvents to dissolve cellulose at the molecular level. Despite the promising role that natural polymers may undertake in the near future in replacing synthetic polymers, still many challenges exist. Here we address the associating polymer features exhibited by native cellulose in solutions with varying IL, in both linear and nonlinear viscoelastic regimes. We observed three aspects attributed to associations between cellulose chains: i) For a given cellulose sample at any particular concentration, the viscoelasticity is very different in the three ionic liquids we study. ii) The concentration dependence of entanglement plateau width is considerably stronger than that of polymer solutions with no associations. iii) The shear stress growth coefficient in steady-shear flow overcomes the complex viscosity, violating the empirical Cox-Merz relationship. We also used the Sticky-Reptation molecular model to estimate the association lifetime and the average number of associating sites from the observed data. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z18.00007: Salt effect on the liquid-liquid phase separation of charged macromolecules Chao Duan, Rui Wang Aggregation behaviors of charged macromolecules are ubiquitous in living cells, which can proceed via liquid-liquid phase separation (LLPS). Salt ions play an important role in controlling the LLPS, for which some abnormal phenomena beyond the mean-field Debye-Hϋckel framework have been increasingly observed such as nonmonotonic salt-concentration effect and specific ion effect. In this work, we developed a theory to study the salt effect on the LLPS of charged macromolecules. In our theory, the localized fluctuation of solutes in the dilute phase is considered and the electrostatic fluctuation is also captured by the self-energy of ions. We find that the solubility shows salting-out behavior at low salt concentrations. At high salt concentrations, it can be either salting-in or salting-out, which depends on the dielectric constant of macromolecules. In addition, the solubility also strongly depends on the chemical identity of ions: it follows the inverse Hofmeister series at low salt concentrations whereas it shows direct Hofmeister series at high salt concentrations. These results are in agreement with experimental observations. Furthermore, we analytically obtained a universal curve determining the borderline between salting-in and salting-out regions, which matches quantitatively with the results of a variety of charged macromolecule systems such as lysozyme, elastin-like polypeptide and PNIPAM in sodium halogen solutions. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z18.00008: Counterion Entropy Impacts on Bulk Phase Behavior in Ether-Based Charge-Neutral Block Copolymers Bradley J Grim, Matthew Green The impact of electrostatics on block copolymer (BCP) thermodynamics has been an elusive inquiry for several decades. While significant progress has been made in unravelling the effects of lithium salt doping in ether-based BCPs, much less is known about pendant charges wherein a critical gap between theory and experiment exists. The largely reduced entropic screening penalty of pendant charges relative to mobile salts forces us to consider enthalpic correlations in much finer detail which can be greatly convoluted by molecular architecture. To help decouple these equilibrium factors, a fundamental understanding of counterion entropy effects is needed. In this work, we use an ether-based platform to compare the effects on phase behavior and dielectric response between two charged species: one where the counterion is mobile, and the other bound as a zwitterion. To our knowledge, this is the first time that backbone-tethered zwitterions have been used to study BCP thermodynamics in the bulk. The BCP of interest was designed specifically to minimize both electrostatic cohesion and preferential ion solvation between phases, thus allowing counterion translational entropy to become the dominant influence on phase behavior. Using dielectric relaxation spectroscopy, small angle X-ray scattering, and rheology, we seek to understand how counterion entropy impacts BCP thermodynamics by coupling microphase morphology and segregation strength to ion dynamics and interactions. |
Friday, March 18, 2022 1:06PM - 1:18PM |
Z18.00009: Self-Assembly of Ultrahigh Molecular Weight Block Copolymers under Dissipative Solvent Vapor Annealing Xiao Li Ultrahigh molecular weight block copolymer (UHMW BCP) (Mn > 500 kg/mol) is dictated by desire to create the material with the larger features size and interdomain spacing above 150 nm to gain the flexibility in further tuning the block architecture across the film. High chain entanglement of UHMW BCP usually results in extremely slow ordering kinetics. Solvent vapor annealing has been used to facilitate the polymer chain mobility by selective solvent swelling and lowering the effective value of Tg. In addition to conventional self-assembly to reach the thermodynamic equilibrium, dissipative self-assembly (DSA) is the out-of-equilibrium process driven by input energy dissipation. However, DSA hasn't been applied to BCP due to temporal control over assembled structures under energy unfavorable conditions. Here, benefiting from the slow molecular dynamics and large domain size from UHMW BCP, the system can be pushed out of equilibrium in a controllable manner. We use Polystyrene-b-poly(2-vinylpyridine) to study how the oscillating manner of the mixture solvent vapors will prevent the system from reaching equilibrium state. The dense packed and ordered micelle structure can be achieved only by dissipating solvent vapor annealing, and the structure varies with the thickness of film. |
Friday, March 18, 2022 1:18PM - 1:54PM |
Z18.00010: “Polymer design in the era of machine learning” Invited Speaker: Juan De Pablo Advances in molecular modeling algorithms, optimization strategies, and machine learning techniques, are rapidly changing the way in which computational tools can be used to design polymeric materials systems or to interpret experimental data. In this presentation I will discuss these ideas by relying on three examples taken from our own research. In the first, I will discuss the automated creation of data bases, and the development of new graph based neural network strategies to represent polymeric structures. I will also discuss how such a framework can then be used to predict the properties of polymers and to design new materials with target properties. In the second, I will discuss how multiscale modeling and machine learning can be used to engineer the structure and, ultimately, the rheology of polymeric materials. In a third example, I will discuss how machine learning can be used to learn or extract physical principles from large data sets, particularly in the context of long-time structural relaxation in ordered polymeric materials. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z18.00011: Preparation of Natural Spider Silk Nanofibrils by Assembling Molecules or Disassembling Fibers Dinidu P Perera, Hannes C Schniepp, Linxuan Li, Qijue Wang, Chloe Walsh Spider silk features a remarkable combination of strength and toughness, which outperform many of the known materials. Additionally, its biocompatibility, biodegradability, and lightweight create numerous potential applications. Despite extensive research, comprehensive experimental evidence of the formation and morphology of the internal structure of this biopolymer is still limited and controversially discussed. Here, we disassembled spider silk fibers by mechanical force and showed that it is completely composed of ≈10 nm nanofibrils aligned in the fiber direction. The extreme stability and the robustness of these nanofibrils reveal that they give birth to fiber's outstanding mechanical performance. Furthermore, we observed that the silk protein possesses an intrinsic mechanism to form nanofibrils of the same dimensions and morphology as the disassembled natural nanofibrils via shear-induced self-assembly, which can be easily triggered in-vitro. Finally, we studied the self-assembly under varying physicochemical conditions and found it is highly sensitive to pH, shear force, ion concentration, and protein concentration. This knowledge helps to understand the fundamentals of this exceptional material, paving the way for the realization of silk-based high-performance materials. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z18.00012: Characterizing the Lithium Ion Coordination in Ionic Liquid Mixtures and Polymer Electrolytes: A Molecular Dynamics Study Kyeong-Jun Jeong, Chang Yun Son Polymer electrolytes (PEs) are actively studied for their potential applications in lithium batteries. In salt-doped dry PEs, negative lithium transference numbers are observed in high salt concentration. This leaves a question about how to effectively control the cation-anion aggregation by polymer-ion solvation in PEs compared to the mixtures of ionic liquids (ILs) with lithium salts. In this work, we develop and import a predictive model for IL electrolytes consisting of Li+, [EMIM+], and [TFSI-], and their mixture with a set of poly(ethylene oxide) (PEO)-based polymers in molecular dynamics simulation. We focus on elucidating the solvation structure of lithium ions with the anion and the polymeric solvent, which provide a molecular interpretation of its effect on the negative transference number. The extent of lithium-anion clustering and its coordination structure is highly sensitive to the electrostatic parameters of the anion/solvent model, which is an unseen trend in neat ILs. Furthermore, in PEs based on PEO the system undergoes rebalancing of lithium solvation by the anion and EO moieties, which had strong influence on the ion transport coefficients of the PE.
This study opens a perspective for fine-tuning molecular interactions to develop high-transference PEs. |
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