Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S19: Structure and Dynamics of Ion-Containing Polymers IIRecordings Available
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Sponsoring Units: DPOLY Chair: Amalie Frishknect, Sandia National Laboratories Room: McCormick Place W-185A |
Thursday, March 17, 2022 8:00AM - 8:12AM |
S19.00001: Effects of Ionic Group Distribution on the Structure and Dynamics of Amorphous Polymer Melts: Molecular Dynamics Simulations Insight Supun S Mohottalalage, Dipak Aryal, Bryce A Thurston, Gary S Grest, Dvora Perahia Decoration of polymers with ionizable groups results in distinctive structures that drive their dynamics. Their structure is dominated by ionic clusters driven by electrostatic interactions. One significant unresolved issue is the impact the of distribution of ionizable groups along the polymer backbone on cluster formation and thus on the dynamics of the polymers. Using fully atomistic molecular dynamics simulations, we study the structure and dynamics of amorphous polystyrene sulfonate with random, precise (number of carbons between ionizable groups is exact), and blocky distributions of the ionizable groups along the backbone. We find that the shape and size distribution of clusters as well as the number of unique chains associated with each cluster are affected by the distribution of the ionic groups. This in turn influences the structure and dynamics of the polymers as expressed in S(q) and S(q,t). Precise and blocky distributions exhibit higher interionic domain correlations compared with a random distribution. The mobility of the polymer and counterions is affected by both the number and size of the clusters as well as the number of polymer chains associated with each cluster. |
Thursday, March 17, 2022 8:12AM - 8:24AM |
S19.00002: Effects of Cluster Cohesion on Structure and Dynamics of Ionizable Polymer Melts at High Ion Contents: Molecular Dynamics Simulations Study Shalika D Meedin, Gary S Grest, Dvora Perahia Ionic clusters control the structure and dynamics of ionizable polymers. Hence, correlation of cluster cohesion with structure and dynamics is crucial to understand their properties. Here, using atomistic molecular dynamics (MD) simulations, we probe the effects of solvent modified ionic assemblies on the structure and inherent dynamics of polystyrene sulfonate (PSS) melts and dense suspensions in the polyelectrolyte regime. PSS melts at different sulfonation fractions (f=0.20-0.55) are incorporated with THF (0-20%) to modify the cohesion of ionic assemblies. The PSS melt at sulfonation fraction ¦= 0.20 forms intermediate size distinguished clusters while at f ≥ 0.35 there is one large percolating cluster spanning the system. Addition of THF breaks the ionic network and enhances polymer mobility. Surprisingly, when adding THF, the minimum average distance between sulfur atoms shifted to smaller dimensions which maybe attributed to releasing constraints between ionic groups and enhancing better packing. Correlation of cluster cohesion with structure and dynamics of solvent modified ionizable polymer melts on multi-time-length scales will be discussed. |
Thursday, March 17, 2022 8:24AM - 8:36AM |
S19.00003: Theory of swelling dynamics of polyelectrolyte gels under external electric fields and geometric constraints Sohyun Jung, Ho-Young Kim Hydrogels are widely used as soft actuators owing to their stimuli sensitivity, flexibility, hydrophilicity, and high swelling ratio. In many hydrogel-based systems, precise control of gel swelling behavior is essential to realize targeted functions or motions. The swelling rate, ratio, and resultant force of given hydrogels are functions of gel size, geometric constraints, magnitude and type of external stimuli. Here, we study the swelling dynamics of polyelectrolyte hydrogel under the effects of external electric fields and geometric constraints. We theoretically model the enhancement of swelling rate and ratio owing to the electroosmotic liquid influx induced by the external electric field. We also theoretically elucidate the build-up process of stress inside geometrically constrained gels. Our theory can guide a design of hydrogel-based actuation systems that require agile response with high stiffness. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S19.00004: Influence of Charge Fraction on the Phase Behavior of Symmetric Charged-Neutral Diblock Copolymers Bo Zhang, Caini Zheng, Michael B Sims, Frank S Bates, Timothy P Lodge Nanostructured polymer electrolytes have gained significant scientific interest as potential replacements for liquid electrolytes in lithium-ion batteries. In this work, a series of poly[(oligo(ethylene glycol) methyl ether methacrylate–co–oligo(ethylene glycol) propyl sodium sulfonate methacrylate)]-block-polystyrene diblock copolymers were synthesized as a model system to probe the effect of charge fraction on the phase behavior of symmetric charged-neutral diblock copolymers. Small-angle X-ray scattering (SAXS) experiments showed that increasing the charge fraction does not alter the ordered phase morphology (lamellar), but increases the order-disorder transition temperature (TODT) significantly. Additionally, the effective Flory-Huggins interaction parameter (χeff) was found to increase linearly with the charge fraction, similar to the case of conventional salt-doped diblock copolymers. This indicates that the effect of counterion solvation, attributed to the significant mismatch between the dielectric constants of the two blocks, provides the dominant effect in tuning the phase behavior of this charged diblock copolymer. Electrostatic interaction is therefore a relatively weak contributor, likely due to the high dielectric constant of the charged block. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S19.00005: Phase behavior of partially charged polymer ternary blends Caini Zheng, Bo Zhang, Timothy P Lodge Single-ion-conducting block copolymers are of great interest due to their potential as solid electrolytes in, e.g., lithium-ion batteries. However, delicate control of polymer composition to optimize the structure-conductivity compromise remains a challenge. Alternatively, blending a block copolymer (A-B) with homopolymers (A/B) offers an easy way to tune the microstructure by just varying the volume ratio of each polymer component. Despite numerous studies on neutral polymer systems, the phase behavior of partially charged ternary blends has not been thoroughly investigated. In this work, we examine the phase behavior of three ternary systems composed of poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)] (POEGMA), polystyrene (PS) and the corresponding block copolymer (POEGMA -PS), with different charge fractions. Small-angle X-ray scattering was used as the primary technique to map out the three-component phase prisms, where large windows of phase coexistence were observed. Additionally, these phase diagrams were found to deviate from symmetry due to the combined effect of charge and conformational asymmetry. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S19.00006: An Investigation of the Phase Behaviour of Poly(ethylene oxide)/Poly(methyl methacrylate) Blend Electrolytes Neel J Shah, Lilin He, Kevin W Gao, Nitash P Balsara In this study, we investigated the effect of added salt on a miscible polymer blend system. The system studied is PEO (8.5 kg/mol) blended with PMMA (47.3 kg/mol) with added LiTFSI salt. We studied the phase behavior of 5 PEO/PMMA blend systems: two majority PEO blends, one symmetric blend and two majority PMMA blends. Utilizing SANS, we found that the majority PEO blends were miscible both in the neat state and at all salt concentrations. We found that the majority PMMA blends were only miscible in the neat state. The symmetric PEO/PMMA blend system was miscible both in the neat state and at all salt concentrations except at r = 0.05, where r is the ratio of moles of Lithium to moles of ethylene oxide. The data points to a complex relationship between salt concentration, blend composition and phase behavior. We quantified the thermodynamics of PEO/PMMA/LiTFSI blends utilizing the framework of de Gennes RPA to calculate an effective χ parameter, χeff, from fits of SANS data. We found that χeff is constant as a function of salt concentration for all blends in this study. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S19.00007: Cluster Cohesion of Ionomer Regime Swollen Melts Chathurika J Kosgallana, Gary S Grest, Dvora Perahia Structure and dynamics of polymer melts in the ionomer regimes are affected by the backbone as well as the ionizable groups. On the path to understanding the immense effect a small number of ionizable groups have on polymer dynamics, the current study probes lightly sulfonated polystyrene melts swollen with THF, using molecular dynamics simulations. Though THF is a polar solvent and interacts predominantly with the ionic clusters, it has limited effects on the backbone conformations which allows the study of the cohesion of the ionic clusters on the polymer structure and dynamics. Cluster characteristics including shape, size and internal dynamic were calculated and correlated with the polymer structure and dynamics as expressed in the static, S(q), and dynamic, S(q,t), structure factors, and mean square displacement (MSD). Surprisingly with increasing THF fraction, larger clusters are formed, suggesting that the solvent releases constraints that allow assembly into larger ionic domains. The cluster boundaries become significantly more defined. In contrast to PSS in toluene, even though the average clusters are larger, segmental dynamics increases. The interrelation between the cluster properties and dynamics will be discussed. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S19.00008: Influence of chain rigidity on ion dynamics in polymerized ionic liquids: Insight from high-pressure dielectric studies Shinian Cheng, Zaneta Wojnarowska, Joshua Sangoro, Marian Paluch Polymerized ionic liquids (PILs) are of great interest in the scientific community due to their potential applications as advanced electrolytes in modern electrochemical devices. Understanding the ion transport mechanism in PILs is critical for designing highly conducting polymer electrolytes. One strategy to bring an essential breakthrough in this issue may be the application of high-pressure techniques. Here, we investigate, over a broad range of temperature and pressure, the ion dynamics of two PILs with different chain rigidity (flexible ethylene oxide vs. rigid vinyl-imidazolium) by using broadband dielectric spectroscopy. The determined pressure coefficient of glass transition temperature and the activation volume of studied PILs indicate that the chain rigidity strongly affects their pressure sensitivity and, thereby, ion dynamics at high-pressure conditions. Additionally, the analysis of high-pressure ion dynamic data using the free-volume-based model established here indicates that the rigid chain significantly reduced the critical volume required for ion hopping and enhanced ion mobility when approaching the glassy state. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S19.00009: Assembly of Ionizable Triblock co-Polymer in THF Solutions John M Bracewell, Supun S Mohottalalage, Gary S Grest, Dvora Perahia Recent efforts to design high energy density light weight capacitors brought to the forefront triblock copolymers that contain ionizable segments. These triblocks of the form ABC, where the end block is highly ionizable, preferably in the polyelectrolyte regime, forms domains that are highly polarizable. The other two blocks provide a structured matrix that separates these ionic domains and provide mechanical stability. Transforming this idea to an actual device requires control over assembly of a complex polymer in the high segregation limit. Here using atomistic molecular dynamics simulations, we follow the assembly of a model triblock co-polymer with tert-butyl polystyrene-b-polyethylene-r-propylene-b-sulfonated polystyrene with sulfonation levels varying from 0 to 95% in dilute solutions THF. THF is a polar solvent that experimentally dissolves the triblock. We find that across all sulfonation levels, the ionizable blocks as well as the t-butyl styrene blocks assume an extended conformation. The rubbery segment however fold to form a nano domain with enhanced order. The talk will further expound on the correlation between the sulfonation levels and the structure dynamics of each of the components in solutions. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S19.00010: Electrostatic interactions and conformations of polyelectrolyte chains Souradeep Ghosh, Arindam Kundagrami In the absence of additional strong electrolytes, polyelectrolyte chains are well known to be strongly correlated in dilute solutions. This work mainly focuses on various interactions in single and many polyelectrolyte chain systems depending upon various physical variables, such as ion sizes, charge densities, temperature, polymer concentration, polymer length, and monovalent salt concentration, related to such interactions. We will present our understanding that we have developed on this topic, especially for two systems - single isolated polyelectrolyte chains and oppositely charged polyelectrolyte chains. The significant results we have obtained show that for a given range of Coloumb strength, the counterion-release picture is valid. It also dominates the interactions for the substitution process involving polyelectrolyte chains. Consequently, the significant binding affinities are governed mainly by the translational entropy of the released ions. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S19.00011: Quantifying the interaction between two polyelectrolyte chains using constraint self-consistent field theory Chao Duan, Luofu Liu, Rui Wang Polyelectrolytes (PEs) are polymers with charged repeating units which have broad applications in surfactants, absorbers, battery electrolytes, and stimuli-responsive functional materials, and are widely used as model systems to study biomolecules such as DNA, RNA, and proteins. The interaction between PE chains essentially governs a wealth of structure and dynamic properties. While interactions between rigid colloidal particles are well characterized by DLVO theory, a systematic description of the interactions between polyelectrolyte globules is still lacking as they are soft, deformable, and can overlap with each other. Here we developed a constraint self-consistent field theory that enables us to quantify the potential of mean force as a function of center-of-mass separation. The theory systematically captures the coupling between the position-dependent of interaction and chain conformation. The potential of mean force shows a long-range repulsion due to the electrostatic force and short-range attraction as the fusion of two polymer chains. Furthermore, we show multiple kinetic pathways for the association of two PEs because of different equilibrium structures of the final associates. This study elucidates that the two-body interaction between soft particles is essentially different from that of rigid particles. The potential of mean force obtained from our work is an important ingredient in the coarse-grained molecular simulations which can be used to study the aggregation and dynamics of charged macromolecules. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S19.00012: Polyelectrolyte complex sponges with pH responsiveness Eyal Zussman, Gleb Vasilyev, Patrick Martin Sponges composed of nanorods or short polymer nanofibers are useful for many applications. The main challenge of creating a 3D skeleton from nanostructured elements stems from the inability to form effective entanglements between individual components. While as an alternative, a possible solution is to form joints by crosslinking individual particles with physical or chemical bonds. Obviously, the structural stability of the skeleton and the effective physical and mechanical properties of sponges are decisively dependent on the material composition and interaction of the links and joints. Our goal is to create sponges with a skeleton made up of links of CNCs (cellulose nanocrystal) and joints made from poly(acrylic acid) and poly(allylamine hydrochloride) that can electrostatically bind the CNCs and respond to pH-stimuli. Rheological measurements of the sponge precursor suspensions proved a massive yield stress increase, indicating strong electrostatic interactions between the overall cationic polyelectrolyte complex (PEC) and anionic CNCs. Cryo-TEM imaging of the suspension confirmed the formation of a global percolated network, consisting of CNC rods, bridged by PEC clusters of 10–20 nm diameter. Freeze-drying of the CNC-PEC suspensions without any further manipulation led to highly porous sponges. The as-prepared sponges were very light (35–93 mg/cm3) and demonstrated a lamellar structure with ~1.5–3 μm lamella thickness and 40–150 μm interlamellar distance. Dry specimens exhibited a compression modulus increase from 7 up to 62 kPa with PEC concentration rise. In response to immersion into water at different pH, the sponges showed morphologically and mechanically pH-responsive behavior. The intensive complexation between sponge constituents is also reflected in a reduced ability to bind charged dyes at neutral pH values. Decreasing the pH results in an increased adsorption efficiency for anionic dyes, while raising the pH improves the cationic dye adsorption. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S19.00013: Response of the Polyelectrolyte Brushes to External Electric Field and the Associated Flow Modifications: An Atomistic Perspective MD Turash Haque Pial, Harnoor S Sachar, Siddhartha Das Polyelectrolyte (PE) brushes are of great importance in countless applications due to their diverse responses to environmental stimuli. Here, we study the effect of external fields on PE brushes using all-atoms molecular dynamics simulations. Our simulations showed that the external axial electric field can reduce the height of the PE brushes significantly. Depending on the charge distribution of their pendant groups, the PE brushes respond to the external electric field in two different ways. When the charge density is high and the counterions are strongly attached to the oppositely charged monomers, the asymmetry in the distribution of the counterions leads to a reduction in the brush height. On the other hand, when the charge density is small and the counterions are not bound to the monomers tightly, the PE brush can tilt in response to the electric field lowering the brush height. We have also discovered that the axial electric field in a PE brush-grafted nanochannel can control the overscreening behavior (inside the PE brush layer), co-ion dominated electroosmotic (EOS) flow and field strength dependent reversal in the EOS flow directions. Finally, this overscreening behavior can lead to simultaneous power generation and flow enhancement under an applied pressure gradient. |
Thursday, March 17, 2022 10:36AM - 10:48AM |
S19.00014: Electrostriction-enhanced giant piezoelectricity via relaxor-like secondary crystals in extended-chain ferroelectric polymers Lei Zhu, Zhiwen Zhu, Guanchun Rui, Elshad Allahyarov, Ruipeng Li, Fabrice Domingues Dos Santos, Hezhi He, Philip L Taylor Piezoelectricity in ferroelectric polymers originates from the electrostrictive effect coupled with a remanent polarization. However, its structural origin remains controversial, and it is not clear how modifying the electrostriction can further improve piezoelectricity for polymers. Here, we report that electrostriction can be significantly enhanced in poled poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] random copolymers containing extended-chain primary crystals and relaxor-like secondary crystals in the oriented amorphous fraction (SCOAF). As a result of the high polarizability of dipoles and ferroelectric nanodomains in the SCOAF, the inverse piezoelectric coefficient d31 reaches as high as 77±5 pm/V for the P(VDF-TrFE) 55/45 copolymer at 55 °C. This finding not only extends our understanding of piezoelectricity in polymers, but also provides guidance for further enhancing the piezoelectricity of ferroelectric polymers in the future. |
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