Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A05: Charged and Ion-Containing Polymers I |
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Sponsoring Units: DPOLY Chair: Aman Agrawal, University of Houston Room: Room 128 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A05.00001: Microphase Segregation of Polyelectrolyte Brushes Takashi Yokokura, Chao Duan, Rui Wang Polyelectrolyte (PE) brushes are widely used as surface modifiers with tunable response to stimuli. A comprehensive understanding of their structure and mechanical behaviors is essential for the rational design of smart materials. Here, we develop a self-consistent field theory (SCFT) which systematically includes polymer elasticity, solubility, and electrostatic interactions in a unified framework. Particularly, the theory well captures the coupling between the chain conformation and the long-range Coulombic force. Applying the theory to a simple system of uniformly charged PE brush, we find that the brush will undergo microphase segregation to form a multi-layered structure as the electrostatic repulsion increases or the hydrophobicity decreases. The calculation of the end-point distribution reveals that multi-layered brushes are formed by collections of melted mushroom conformations grafted upon each other instead of a pearl-necklace conformation for each chain. To facilitate the experimental validation of the multi-layered structure, the corresponding reflectivity spectra have also been provided. Furthermore, the theory is also applied to describe brushes formed by intrinsically disordered proteins. The theoretical prediction of the salt concentration dependence of the brush height shows quantitative agreement with the experimental measurements. The dramatic change of the brush height near a critical salt concentration is explained by the transition of a purely coil-like layer to a condensed layer coexisting with a coil-like layer. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A05.00002: Electrostatic Correlation Induced Charge Inversion and Nonmonotonic Conformational Change of Polyelectrolyte Brushes Chao Duan, Rui Wang Polyelectrolyte brushes are widely used to regulate transport of ions and molecules, control wettability, adhesion, and lubrication of surfaces. The conformation of brushes is of particular importance which can respond to external stimulus such as salt ions. In the presence of multivalent ions, there are many phenomena observed in experiments and simulations, such as the nonmonotonic dependence of brush height on salt concentration and diminish of the lubricity, cannot even be qualitatively explained by existing theories. Here, we develop a new theory which incorporates the Gaussian renormalized fluctuation theory for charged systems into the self-consistent field theory for polymers. Particularly, the correlation between charged segments and mobile ions are fully accounted for. The coupling between chain conformation and electrostatic effects is also captured self-consistently. For monovalent salt ion, we find that the height of brushes decreases monotonically as salt concentration increases, consistent with the mean-field prediction. However, for divalent salt ion, brushes collapse at low salt concentrations but re-expand as the salt concentration further increases due to electrostatic correlation. Furthermore, for trivalent salt ion, besides the re-expansion of brush height, both the density profile of polymers and the distribution of salt ion exhibits an oscillating behavior, which indicates stronger correlation. We reveal that the re-expansion of the brush is accompanied by the phenomenon of charge inversion where multivalent counterions overcompensate the total charge carried by the polyelectrolyte chains. |
Monday, March 6, 2023 8:24AM - 8:36AM |
A05.00003: Role of polymer architecture and interfacial mixing on ion transport in linear-brush polyether-based block copolymer electrolytes Regina J Sánchez, Benjamin Ketter, Joshua A Mysona, Chuting Deng, Whitney Loo, Daniel Sunday, Juan J De Pablo, Shrayesh Patel, Paul F Nealey Polyether-based block copolymers, in which two or more blocks self-assemble into phase-separated nanostructures, are of great interest for use as solid polymer electrolytes for lithium ion batteries as the constituent blocks can be independently tuned to impart multiple desirable, yet orthogonal thermal, mechanical, and electrochemical properties to the resulting material. Previous experimental and simulation work focused on linear-linear polyether-based block copolymer electrolytes, particularly PS-PEO/LiTFSI, found ionic conductivity to be highly dependent on segregation strength and that disruption of the solvation sites connectivity derived from interfacial mixing of PS with PEO is a more likely explanation for the lower conductivity typically observed near domains interface rather than just differences in glass transition temperature between blocks. [1] A clearer understanding on the relationship between polymer architecture and interfacial mixing with ion conduction, however, is still missing. In this work, we explore the role of polymer architecture and interfacial mixing on the ion transport in linear-brush block copolymer electrolytes as a function of side-chain length of the brush block. To this aim we prepared a series of lamella forming block copolymers with LiTFSI, specifically poly(trifluoroethyl methacrylate)-b-poly(ethylene glycol methyl ether methacrylate) (PTFEMA-b-POEM) to probe the effect of the branched architecture on the ionic conductivity, and further characterized them by impedance spectroscopy, vibrational spectroscopy, and soft X-ray reflectivity to determine and compare the ionic conductivity, degree of dissociation, polymer dynamics as well as the interface characteristics of such materials. In addition, we coupled molecular dynamic simulations to the experimental work to gain insights of the mechanisms and barriers to ion transport near the domain interface at the molecular level. Overall, we found polymer architecture and interface characteristics play a big role in determining conductivity in these systems. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A05.00004: Effect of ionic strength and salt identity on swelling behavior of weak polybasic brushes with various charge fractions Farshad Safi Samghabadi, Shahryar Ramezani Bajgiran, Amanda B Marciel, Jacinta C Conrad Charged polymer brushes offer enhanced properties compared to neutral brushes due to the intra- and interchain interactions between charged monomers. These interactions can be tuned through the charged monomer fraction and by modulating environmental conditions such as solution pH and ionic strength. Here, we examine the effect of salt concentration and identity on the conformational pH-response of weak polybasic brushes with various charged monomer fractions using in-situ ellipsometry and streaming zeta potential. Our model system consists of random copolymers of weakly charged 2-(dimethylamino)ethyl acrylate (DMAEA) and neutrally charged 2-hydroxyethyl acrylate (HEA). We synthesize polymer brushes with charge fractions ranging from f = 1 to 0 at constant grafting density using surface-initiated copper(0) controlled radical polymerization (SI-CuCRP). Brushes exhibit hysteretic memory behavior in pH-induced swelling and collapse transitions. The extent of hysteresis, however, depends on both charge fraction and the solution ionic strength. The brush isoelectric point varies with the monomer charge fraction, suggesting that the extent of electrostatic interactions on polyelectrolyte brushes affects their physical and chemical properties. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A05.00005: Electrospun nanofiber membranes from polyampholyte/ poly(vinylidene fluoride) blends Anuja S Jayasekara, Luca Mazzaferro, Ayse Asatekin, Peggy Cebe Polyampholytes are amphoteric macromolecules containing randomly mixed oppositely charged groups. Due to the positively and negatively charged moieties on different monomers, polyampholytes show excellent anti-fouling properties and are used extensively in filtration applications. In this study, we electrospun nanofibrous membranes from a random polyampholyte amphiphilic copolymer (r-PAC) blended with poly(vinylidene fluoride) (PVDF) a commercially available semi-crystalline polymer that shows excellent hydrophobic properties. The r-PACs are composed of monomers that are either hydrophobic (2,2,2-trifluoroethyl methacrylate); positively charged ([2-(methacryloyloxy) ethyl]trimethylammonium chloride); or negatively charged (methacrylic acid). In the electrospun membranes, fouling resistance is provided by hydrophilic units of r-PAC and mechanical and chemical stability is provided by PVDF and hydrophobic units in r-PAC. The blend composition was varied by controlling the ratio of PVDF to r-PAC. The electrospun fiber mats were characterized for their structure using wide-angle X-ray scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy. Degradation temperature and glass transition properties were evaluated using thermogravimetric analysis and differential scanning calorimetry, respectively. Hydrophilicity was evaluated using sessile drop contact angle measurements. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A05.00006: Effects of chemical structure variation and salt addition on the glass transition behavior of polyzwitterion/LiCl salt complexes John Thomas, Abhishek Mondal, Ayse Asatekin, Peggy Cebe Using temperature modulated differential scanning calorimetry (TMDSC), the glass transition process and the solid-state heat capacity of polyzwitterion (PZI) / LiCl salt complexes were investigated. Our goal is to characterize the influence of chemical structure variation and salt ratio on the formation of dipole-dipole sidechain electrostatic crosslinks. Starting with poly(sulfobetaine methacrylate), PSBMA, as the parent polymer, changes to the backbone and sidechain chemistries resulted in the following PZIs: poly(sulfobetaine acrylate), PSBA; poly(ethyl sulfobetaine methacrylate), PESBMA; poly(sulfobetaine-4vinylpyridine), PSB4VP; and poly(sulfobetaine-2vinylpyridine), PSB2VP. These changes result in variation of the onset of thermal degradation, the level of water uptake, and the solid and liquid state specific heat capacities. The PZI/LiCl complexes are both hydroscopic and hydrophilic, and bound water results in plasticization of the glass transition. Thermogravimetric analysis (TGA) quantified the change in mass with temperature during water removal. To accurately determine the effects of LiCl on the system bound water must be eliminated to achieve a dry solid state. For the dry PZI, as the molar ratio of LiCl increases, the glass transition temperature is lowered, and the heat capacity increment at the glass transition temperature is increased. These results are consistent with a model where the number of dipole-dipole crosslinks is decreased as LiCl content is increased. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A05.00007: Shape asymmetry of polyelectrolytes in dilute solution Christian A Aponte-Rivera, Michael Rubinstein The asymmetric shape of polyelectrolytes is important to predict their thermodynamic and dynamic properties. Although it is well established that electrostatic repulsion stretches polyelectrolytes to a size larger than that of a neutral chain with the same number of monomers, whether this stretching occurs solely in one direction is not well understood. Previous theoretical models assume stretching occurs solely along a longitudinal (or principal) axis and that the size of the chain perpendicular to this axis (i.e., the minor axis) remains unperturbed. However, simulations have reported polyelectrolytes are stretched along the perpendicular direction, an observation that cannot be explained by current theories. Here, we conduct simulations of isolated polyelectrolytes and quantify their size and shape. Results from polyelectrolyte simulations are compared to simulations of neutral force-stretched chains with an equal number of monomers as a control. We find that electrostatic repulsion in polyelectrolytes results in stretching along the perpendicular direction, while force-stretched chains remain unperturbed in the direction perpendicular to the force. To quantify stretching on different length scales, we compute the mean-square amplitude of the chain normal modes. Furthermore, we develop a scaling model that predicts the perpendicular size of polyelectrolytes and agrees with simulations. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A05.00008: Synthesis and Properties of Cationic Multiblock Polyaramides and Polyimides Alison Biery, Daniel M Knauss Polydiallyldimethylammonium chloride (PDADMAC) is a useful material due to its high charge density and alkaline stability, but its hydrophilic nature limits applications to those where a dissolved polymer is suitable. To make polymers containing the diallyldimethylammonium moiety for applications as films and membranes, multiblock copolymers of polyaramides and polyimides, materials known for their excellent physical properties, were synthesized. Aminophenyl difunctionalized PDADMAC was synthesized using a disulfide iniferter then counterion exchanged to the hexafluorophosphate anion to produce telechelic oligomers with good solubility in polar aprotic solvents. The oligomers were reacted in-situ with the proper difunctional monomers to produce poly(ether)aramides and poly(ether)imides. The copolymers were synthesized at high yield over a range of compositions and the material properties resulted from both the backbone chemistry and composition. Several of the copolymers formed films with good clarity, strength, and flexibility. The copolymers containing ether linkages had increased backbone flexibility and better film properties. The multiblock copolymers demonstrate a method to produce materials with good thermal stability, strength, and flexibility, making them uniquely capable of serving as water insoluble, cationic films and membranes. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A05.00009: Coarse-Grained Explicit-Solvent Molecular Dynamics Simulations of Unentangled Polyelectrolyte Chains in Semidilute Solutions Jan-Michael Carrillo, Yangyang Wang, Rajeev Kumar, Bobby G Sumpter We present results of explicit solvent coarse-grained molecular dynamics simulations of fully charged, salt-free, and unentangled polyelectrolytes in semidilute solutions. The inclusion of a polar solvent in the model allows for a more accurate representation of these systems at higher concentrations, where the assumptions of a continuum dielectric medium and screened hydrodynamics break down. The collective dynamic structure factor of polyelectrolytes, S(q,t), showed that at q > q*, where q*=2π/ξ is the polyelectrolyte peak in S(q) and ξ is the correlation length, the average relaxation time fitted from a stretched exponential was <τ> ~ q-3, which describes Zimm-like dynamics and un-screened. This is in contrast to implicit solvent simulations using a Langevin thermostat where <τ> ~ q-2. At q < q*, a cross-over region was observed that eventually transitions to <τ> ~ q-2 at length scales larger than ξ for both implicit and explicit solvent simulations. The simulation results were also compared to scaling predictions for correlation length, ξ ~ c-1/2, specific viscosity, ηsp ~ c1/2, and diffusion coefficient, D ~ c0, where c is the polymer concentration. The scaling prediction for ξ holds, however deviations from the predictions for ηsp and D were observed for systems at higher c. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A05.00010: Salt effect on the viscosity of semidilute polyelectrolyte solutions of NaPSS Andrey V Dobrynin, Michael Jacobs, Carlos G Lopez, Anish Gulati We elucidate properties of aqueous solutions of sodium polystyrene sulfonate (NaPSS) by analyzing solution viscosity as a function of polymer and salt concentrations in the framework of the scaling model. This approach is based on a scaling relationship between solution correlation length ξ=lgν/B and number g of monomers per correlation volume for chains with monomer projection length l. The specific values Bpe, Bg, Bth, and of the B-parameter corresponding to exponents ν =1, 0.588, and 0.5 are determined by the fraction of charged monomers and their degree of ionization, the effective solvent quality for the polymer backbone and the chain Kuhn length. The values of the B-parameters were obtained from the plateaus of normalized specific viscosity ηsp/Nw(cl3)1/(3v-1) as a function of the monomer concentration c for polyelectrolytes with weight average degree of polymerization, Nw. This information was used to construct a diagram of different solution regimes, calculate the fraction of free counterions, and the energy of the electrostatic blobs. By extending a scaling approach to entangled solutions, we determine the packing number for chain of corelation blobs and established crossover concentration to the entangled solution regime. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A05.00011: Ionization and Conformation Consistency in Weak Polyelectrolytes Near Interfaces Alejandro A Gallegos, Jianzhong Wu, Zhen-Gang Wang In contrast to strong polyelectrolytes, weak polyelectrolytes present electrostatic charges in accordance with the solution pH and the local chemical environment. The pH-responsive behavior is advantageous for applications in smart systems to achieve specific functions such as targeted drug delivery and controlled release. Unfortunately, a quantitative description of such behavior remains challenging. In an inhomogeneous fluid such as near an interface, these important inter- and intrachain correlations effect play a key role in the interfacial behavior which is not accounted for in current theoretical approaches. By coupling a molecular thermodynamic model for chemical reactions with the polymer density functional theory (DFT), we can incorporate these correlation effects to describe the interfacial behavior of weak polyelectrolytes in good agreement with experimental data. We demonstrate that the long-range two-body intrachain correlations can be incorporated into the so-called single-chain-in-DFT simulation to accurately capture the self-consistency between ionization and conformation in weak polyelectrolytes. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A05.00012: Generic Coarse-Grained Molecular Dynamics Simulations of Ion-Containing Polymers Mengdi Fan, Lisa M Hall Ion-containing polymers can be challenging to model due to their strong ion-ion and ion-polymer interactions as well as important features on disparate length and time scales arising from ion, segmental, and overall chain behavior. We study ion-containing systems starting from a generic Kremer-Grest type of model that captures monomer packing and noncrossability of chains and adding long-ranged Coulomb interactions between ions scaled by a background dielectric constant. Depending on the system, further features such as adjusted monomer-monomer interactions to account for chemical differences in copolymers, adjusted monomer and ion sizes, and special ion-monomer potentials to account for ion solvation can be added. Copolymeric systems are especially complex as they may have microphase separated regions with significantly different dielectric strengths and degrees of ion solvation. We typically apply a uniform background dielectric strength; we set this to represent the average dielectric strength for mixed systems or the higher dielectric medium for strongly microphase separated systems (in which the ions exist in the higher dielectric microphase). We also adjust the higher dielectric monomer to ion interactions, often using an ion-monomer potential of the same form as the interaction between an ion and an induced dipole. Recently, we instead applied a classical Drude oscillators model to account for both ion solvation and dielectric strength effects in a greater level of detail. Specifically, polarizable monomer beads are represented by a partially charged bead (that is otherwise similar to the beads of the prior model) with an oppositely charged Drude particle attached to its center by a strong spring. Here we will discuss the implications for ion solvation effects and computational expense. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A05.00013: Effect of solvent-counterion interactions on polyelectrolyte solution properties Can Hou, Carlos G Lopez Polyelectrolytes are used as industrial and commercial thickeners, as they are water-soluble and enhance viscosity [1], but are insoluble in many organic solvents, which limits their applicability in products such as hand sanitisers. Here, we study how counterion-solvent interactions influence the solubility of polyelectrolytes. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A05.00014: Molecular Insights into the Hydration of Zwitterionic Polymers Sara A Tolba Preventing ice formation and accumulation on solid surfaces has always been a great challenge to address for various applications. By applying anti-icing coating on surfaces, we can efficiently reduce ice formation and adhesion. Recently, the new development of zwitterionic polymer coatings attracted a lot of attention due to their excellent anti-icing performance. Herein, we used Density Functional theory (DFT) to present a comprehensive understanding of the hydration behavior of two representative zwitterionic polymers, i.e., poly-sulfobetaine (polySB) and poly-phosphorylcholine (polyMPC), to unveil the molecular mechanism of their excellent anti-icing performance by providing a clear physical and chemical understanding of water-polymer interaction. The bonding analysis by crystal orbital Hamilton populations (COHP) showed strong interaction and covalent-nature bonds between the hydrogen atoms in water molecules and polymers' oxygen atoms. Electron density of states (DOS) and Bader charge analysis both further demonstrated the chemical nature of the water-polymer bonds. Interestingly, our modeling results also revealed that the addition of more water molecules will decrease the stability of the bond between adsorbed water molecules to the polymer. ? Such induced bond instability, along with the polymer's hydrophilic character, suggests that continuous association and dissociation of bonded water molecules serve as the key mechanism of inhibition of water clustering. |
Monday, March 6, 2023 10:48AM - 11:00AM |
A05.00015: Effects of Ion Solvation in a Mixture of Polar Solvent and Polymer Issei Nakamura, Cameron Shock, Jester N Itliong, Mark J Stevens, Amalie L Frischknecht The effect of the strong electrostatic field near ions dissolved in polar liquids causes substantial deviations from the standard theory of ion solvation based on linear-dielectric response theory. We consider this problem in a mixture of polar solvent and polymer by developing a polymerized Stockmayer-fluid (dipolar molecule) simulation method that accounts for the chain statistics and molecular polarization at the molecular scale. Our molecular dynamics simulations suggest that the dielectric constant of the mixture follows Landau-Lifshitz-Looyenga's formula, instead of the number fraction-weighted average. We also show that the ions in the polymer-rich phase tend to be solvated preferentially by polar solvents, tightly bound to the solvent molecules. However, the ion-solvent affinity decreases as the solvent content increases. We discuss how these two competing effects yield a qualitative difference in the simulated solvation energy from the conventional energy expression. |
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