Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C55: Polyelectrolyte Complexation II: Structure and RheologyFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY DBIO Chair: Debra Audus, NIST -Natl Inst of Stds & Tech Room: LACC 515A |
Monday, March 5, 2018 2:30PM - 2:42PM |
C55.00001: Field-theoretic simulations of discrete Gaussian chain polyelectrolytes as a model for coacervation in intrinsically disordered peptides. James McCarty, Kris Delaney, Glenn Fredrickson, Joan-Emma Shea Recent experimental observations of coacervation in intrinsically disordered peptides (IDPs) have raised intriguing questions about their role in IDP aggregation and fibrilization. At the theoretical level such systems are challenging due to the heterogeneous but highly specific sequence of amino acids which constitute IDPs as well as by the subtle but important short-ranged interactions between amino acids in an aqueous solvent. Additionally, phosphorylation, pH, and specific mutations can alter the distribution of charged residues and thereby affect the propensity for coacervation. Here we present field-theoretic simulations of the fully fluctuating Hamiltonian for polymers modeled as discrete Gaussian chains with specific charged residues. Such simulations represent an approximation-free attempt to show how the phase diagram depends on the sequence of charges along the protein backbone, the presence of salts, and the polymer excluded volume. We also compare with coarse-grained molecular dynamics simulations and discuss the relevance for understanding experiments of real proteins. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C55.00002: Transfer-Matrix Description of Complex Coacervation Tyler Lytle, Charles Sing Oppositely-charged polyelectrolytes can undergo associative phase separation in a salt solution via a process known as ‘complex coacervation.’ A notable amount of research has focused on using field-theory extensions of Voorn-Overbeek theory to understand coacervation. However, these methods have difficulty resolving molecular-level features, especially in high charge-density polyelectrolytes. An alternative understanding of coacervation is counterion condensation and release, which postulates coacervation is accompanied by a large change in entropy. The source of this large entropy change is the replacement of a polyelectrolyte’s condensed counterions with the oppositely-charged polyelectrolyte, because the polyelectrolyte’s translational entropy is far less than the counterion’s translational entropy. Inspired by this idea, we have developed a transfer-matrix based theory to describe coacervation in terms of monomer adsorption states. The theoretical values used by this theory are informed by Monte Carlo simulation, and can describe the effects of molecular-level features using physically motivated arguments. This theory could be used in conjunction with more sophisticated theoretical formalisms, thus providing a starting point to describe coacervate-driven self-assembly. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C55.00003: Phase Behavior and Salt Partitioning in Polyelectrolyte Complexes Lu Li, Samanvaya Srivastava, marat andreev, Matthew Tirrell, Juan De Pablo Polyelectrolyte complexes, resulting from associative phase separation of oppositely charged polyelectrolytes, are omnipresent both in nature and technological world. However, the true phase behavior of complexes remains poorly understood. Here we demonstrate complementary experiments and a well-defined simulation model to unveil the complete description of the phase behavior of polyelectrolyte complexes, improving understanding of underlying physics of polyelectrolyte complexation. Experiments with model polypeptides lead to phase diagrams with compositions of the complex and the supernatant, which were in agreements with simulations predictions. Surprisingly, contrary to the widely accepted theory for complexation, we find preferential partitioning of salt ions into the supernatant phase. Upon increasing the salt concentrations, the salt partitioning underwent a unique trend exhibiting a distinct minimum. These trends were revealed by simulations to be strongly influenced by the excluded volume interactions, which were overlooked in the earlier theories. |
Monday, March 5, 2018 3:06PM - 3:42PM |
C55.00004: Coacervation of Oppositely Charged Polyelectrolytes: Effects of Composition Asymmetry Invited Speaker: Zhen-Gang Wang Using a simple liquid-state theory that accounts for electrostatic correlation by the mean-spherical approximation and chain connectivity by the first-order thermodynamic perturbation theory, we study the phase behaviors of a concentration-asymmetric mixture of polycation and polyanion solutions. We construct the full three-dimensional polycation--polyanion--cation concentration phase diagram at a fixed Bjerrum length and use this phase diagram to study the titration behavior of a polycation solution by varying amount of an equal-concentration polyanion solution, both in the absence and presence of added salts. We find that coacervation takes place within a window of volume ratios between the two solutions, when the concentration of the polyelectrolytes (PEs) and/or small ions in the initial solutions is not too high. Furthermore, the partition of the extra PE of the major components and of excess small ions shows qualitatively different behaviors for slightly asymmetric mixtures than for highly asymmetric mixtures. In addition, for salt-free or low salt concentration mixtures, the Galvani potential exhibits an abrupt jump across the symmetry point along the titration path. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C55.00005: Structure, Chain Conformations and Dynamics of Polyelectrolyte Complexes Samanvaya Srivastava, Amanda Marciel, Matthew Tirrell Investigations of structure, chain conformations and dynamics in polyelectrolyte complex (PEC) comprising model polyelectrolytes are presented. The use of charged polypeptides – (poly)-lysine and (poly)-glutamic acid allowed facile tuning of the system parameters, including chain length. side-chain functionality and chirality, while preserving the backbone architecture and chemical structure. Systematic studies using small-angle X-ray scattering (SAXS) of the structure and chain behavior in liquid PEC coacervates revealed a physical description of these materials similar to strongly screened semidilute solutions of polyelectrolytes comprising oppositely charged chains. At the same time, solid PECs were found to be composed of hydrogen-bonding driven stiff ladder-like structures with large correlation lengths. While the liquid complexes behaved akin to semidilute polyelectrolyte solutions upon addition of salt, the solids were largely unaffected by it. The dynamics of the chains in PEC coacervates, explored by rheology measurements, revealed a Maxwell liquid-like behavior. Time-salt superposition led to excellent superposition of the dynamic moduli data, although with the shift factors varying more strongly than previously reported with increasing salt concentration. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C55.00006: Charge Density-Dependent Phase Behavior and Rheology of Polyelectrolyte Complex Coacervates Frances Morin, Jennifer Laaser We investigate the phase behavior and rheology of polyelectrolyte complex coacervates with varying charge density. The coacervates are prepared from poly(acrylic acid) (PAA) and poly(dimethylamino ethyl methacrylate-stat-di(ethylene glycol)methyl ether methacrylate) (P(DMAEMA-stat-DEGMA)), where the P(DMAEMA-stat-DEGMA) copolymers are prepared with the same number of protonatable DMAEMA units per chain but varying overall charge density. We characterize these coacervates by optical turbidity, NMR spectroscopy, gravimetric analysis, and small-amplitude oscillatory shear rheology. We find that decreasing the polycation charge density decreases both the critical salt concentration and the polymer concentration in the coacervates, and shifts the overall relaxation of the materials to faster timescales. The crossover frequency, for example, increases by an order of magnitude with incorporation of just 25 mol% uncharged DEGMA units in the PDMAEMA chains. Our results indicate that cooperativity between adjacent charged sites plays a significant role in the timescale of the “sticky” interactions between chains, and add to the growing evidence that charge density is an important variable for understanding and controlling the physical properties of coacervate systems. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C55.00007: Phase Behavior and Interfacial Tension of Polyelectrolyte Complex Coacervates Samim Ali, Anand Rahalkar, Vivek Prabhu Complex coacervation occurs when a solution of anionic and cationic polyelectrolytes undergoes liquid-liquid phase separation under suitable conditions. The viscoelastic polymer-rich phase (coacervate) exhibits a low interfacial tension with the polymer-poor supernatant. This tunable phase behavior, under different physicochemical conditions, enables the applications of coacervates as encapsulation media and spreadable wet adhesives, for example. This presentation describes an experimental measurement method of the ultralow interfacial tension by combining thermal-induced microphase separation and droplet-retraction analysis. The effect of salt concentration, temperature and molecular mass on the interfacial tension will be discussed and compared to available mean field theory predictions. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C55.00008: Evaporation of Polymer Solutions Containing both Polycations and Polyanions: A Molecular Dynamics Study Chengyuan Wen, Yanfei Tang, Shengfeng Cheng Polyelectrolyte solutions show rich physical behavior different from that of solutions of neutral polymers. For example, in a solution of both polycations and polyanions the complexation of oppositely charged chains can lead to complex coacervates that contain most of the two polymers. Such equilibrium phenomena have been studied for many decades. However, other nonequilibrium processes such as the evaporation of polyelectrolyte solutions have received less attention. We use molecular dynamics simulations to study the evaporation of solutions containing both polycations and polyanions. The polymers are represented by MARTINI-type bead-spring chains. Water is used as the solvent and modeled with a model taking into account polarization effects. Counterions and salts are explicitly included as mobile single beads. The effects of polymer concentrations, salt concentrations, and evaporation rates on the structure of the final polymer film are clarified. The connections of the film structure to the complexation behavior of polyelectrolytes prior to evaporation are elucidated. Our results reveal potential new strategies of fabricating polyelectrolyte films with controlled structures. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C55.00009: Dynamics in Polyelectrolyte Complex Materials Yalin Liu, Whitney Blocher, Xiangxi Meng, Matthew Labbe, Elizabeth Voke, Caleb Boucher, H. Henning Winter, Maria Corradini, Jessica Schiffman, Sarah Perry Recent efforts have dramatically enhanced our understanding of the thermodynamic phase behavior of polymer-based complex coacervates. Extending this knowledge to include the molecular mechanisms that dominate the dynamics of polyelectrolyte complexes is the next critical step in enabling the intelligent design of these materials. We utilize traditional linear viscoelasticity measurements in parallel with novel optical and fluorescence based methods for characterizing the dynamic mechanical response of various polyelectrolyte complex materials as a function of polymer chemistry, length, architecture, the patterning of charge and/or hydrophobicity along the polymer, and solution conditions. These results provide a molecularly-informed understanding of how intermolecular interactions in complex coacervates affect the processability of these materials in applications ranging from spin coating to electrospinning. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C55.00010: Coarse-grained model for polyelectrolyte complexation Marat Andreev, Lu Li, Samanvaya Srivastava, Matthew Tirrell, Alexandros Chremos, Vivek Prabhu, Jack Douglas, Juan De Pablo Self-assembly based on co-polyelectrolyte complexation offers new opportunities for materials design. Here, oppositely charged polyelectrolytes undergo an associative process of phase separation, driven by the entropy gain associated with the release of counter-ions. Homopolymers typically self-assemble into coacervates, while block copolyelectrolytes form micelles or hydrogels. In this study, we aim to quantitatively reproduce experimental results for the phase behavior and rheology of coacervates with a coarse-grained model. Specifically, we focus on three features of the coacervate. First, there is a strong dependence of polymer concentration on the added salt concentration. Second, we show that salt is generally expelled from the coacervate phase and that our model is capable of capturing the salt partition coefficient between the coacervate and supernatant phases. Third, the model enables calculation of the mechanical response and it compares well with experimental measurements. Moreover, it captures changes in the relaxation time as a function of added salt concentration, a phenomenon referred to as "time-salt superposition". We explore the effects of model parameters on the above features of coacervates, and explain the role of short range interactions and ionic strength. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C55.00011: Solution Assembly and Behavior of Modular RAFT Block Polyelectrolytes Jeffrey Ting, Hao Wu, Olivia Werba, Deborah Schneiderman, Abraham Herzog-Arbeitman, Joseph Mitchell, Samanvaya Srivastava, Matthew Tirrell The advancement of ion-containing synthetic polymers towards functional applications relies on elucidating structure-property relationships that often involve interplay between chemically–driven and electrostatic interactions. To this end, the materials dynamics and temporal evolution of polyelectrolyte complex (PEC) assemblies are not well understood, especially non-canonical compared to non-charged counterparts. Herein, we systematically explored PECs by utilizing a RAFT block polymer platform. This approach allowed us to tune polymer microstructure and functionalize labile chain ends, enabling control of assembly size and the ability to monitor in situ diffusivity. Complementary scattering and spectroscopy provided structural information on micellar PEC formation as a function of polymer combination, concentration, and salt. These findings highlight how the rational pairing of well-defined, evolving PECs can reveal path-dependent processing pathways over relevant length- and time-scales, thereby guiding future prediction capabilities and accelerating complex materials development for end-use technologies. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C55.00012: Ion Association in Polyelectrolyte Solutions: Effects of Charge Correlations and Connectivity Sean Friedowitz, Jian Qin Reversible counterion association equilibria in polyelectrolyte solutions is strongly affected by interactions between dissociated ionic species. Previous theories have treated this effect using the Debye-Hückel (DH) free energy, and frequently neglected correlations due to charge connectivity. We demonstrate that straightforward application of the DH free energy implies a reduction in the degree of ion association as charge concentration increases. This unphysical behavior is found to stem from improper regularization of the ion self-energy, an issue we remedy by introducing a smeared charge density. We then show that charge connectivity enhances the propensity for counterion binding along the polyions. The effects of connectivity on the demixing phase behavior of polyelectrolyte solutions are also discussed. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C55.00013: Coupling of Polyelectrolyte Chain Structure with Correlations and Phase Behavior Kevin Shen, Zhen-Gang Wang Using a renormalized Gaussian fluctuation (RGF) field theory that self-consistently accounts for the concentration-dependent coupling between chain structure and electrostatic correlations [Shen and Wang 2017, JCP 146 (084901)], we study the phase behavior of polyelectrolyte solutions. We show that the popular fixed-Gaussian-structure RPA (fg-RPA) greatly over-predicts the driving force for phase separation of charged polymers, even below the critical Manning charge density. This over-prediction is attributable to inaccurate short wavelength chain structure -- while the chain structure is most obviously non-Gaussian at low salt or polymer concentration, the chain's stiffening persists in semi-dilute solution and can qualitatively affect the phase diagram. The RGF's self-consistent renormalization of the chain structure relaxes electrostatic interactions, and better describes much higher charge fractions and a wider concentration window than the regime of validity of fg-RPA. Our work demonstrates how chain structure has important couplings with electrostatic fluctuations and thermodynamics, even before stronger correlation effects like counterion condensation become important. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700