Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C52: Polyelectrolyte Complexation II: Phase Behavior and Solutions DynamicsFocus
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Sponsoring Units: DPOLY DBIO Chair: Samanvaya Srivastava, University of California, Los Angeles Room: BCEC 253B |
Monday, March 4, 2019 2:30PM - 2:42PM |
C52.00001: Polyelectrolyte solution confined between oppositely charged dielectric surfaces DEBARSHEE BAGCHI, Trung Nguyen, Monica Olvera de la Cruz We study a polyelectrolyte solution confined between two oppositely charged dielectric surfaces by a coarse-grained molecular dynamics simulations. Randomly charged beads as in sodium polystyrene sulfonate with varying degrees of sulfonation are modeled using implicit solvent with explicit ions. The charged electrodes that confine the polyelectrolyte solution are considered to be made of a low dielectric constant material such as graphene. We employ an efficient algorithm for computing the induced charges and investigate various properties of our system, such as the capacitance and its relation to the polymer conformation and charge density. We observe counter-intuitive phenomena such as charge amplification where a layer of ions adsorb close to a surface of same charge to allow more polymer adsorption. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C52.00002: Incorporating Molecular Structure into a Transfer Matrix Theory of Complex Coacervation Tyler Lytle, Charles Sing Polymeric complex coacervation is a phase-separation process involving two oppositely-charged polyelectrolytes in an aqueous salt solution, where a polymer-dense phase is formed due to electrostatic interactions between the polyelectrolyte species. The resulting coacervate materials have seen widespread use in industry as viscosity modifiers and encapsulants, and are used in polymer research as an interaction motif for charge-driven self assembly. Despite this utility, a fundamental physical description of this process has remained elusive; a recent resurgance of interest in coacervation has led to a number of candidate theories. Here we present a transfer matrix theory that maps coacervate structure to a one-dimensional adsorption model, leading to a theory that can predict both coacervate phase behavior and local charge correlation features. We show that straightforward modifications to the theory can be used to account for a number of molecular features, including divalent ions, linear charge density, polymer stiffness, and polymer architecture. Comparison to simulation and experiment shows that we can capture qualitative trends that inform the molecular design of polymer complex coacervates. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C52.00003: Structure-Property Relationships for Oligonucleotide Polyelectrolyte Complex Micelles Jeffrey Vieregg, Michael Lueckheide, Alex Marras, Matthew Tirrell When a charged-neutral hydrophilic block copolymer is mixed with an oppositely-charged polyelectrolyte, micro-phase separation occurs, producing core-shell nanoparticles referred to as polyelectrolyte complex micelles by analogy to hydrophobically-driven micellization. PCMs have been proposed as a solution to the urgent problem of therapeutic delivery of (anionic) oligonucleotides into cells, as the dense polyelectrolyte core and neutral corona can shield the oligonucleotides from degradation and improve biodistribution. Several promising results have been reported, but until recently no structure-function relations existed to guide design of PCMs, and little data existed on the effect of chemical modifications to either polyelectrolyte. By combining small-angle X-ray scattering, multi-angle light scattering, and cryo-electron microscopy, we have characterized the morphology and internal structure of PCMs formed by oligonucleotides of varying size, structure, and chemical composition with poly(lysine)-poly(ethylene glycol) block copolymers. I will present results that illustrate the connections between molecular features and PCM morphology, as well as rules for producing oligonucleotide PCMs of desired size and shape with exceptionally low polydispersity. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C52.00004: Probing the size of coacervate core micelles Debra Audus, Brady Garringer, Hayley Boigenzahn Coacervate core micelles, composed of diblock copolymers with oppositely charged blocks forming the core and neutral, hydrophilic blocks forming the corona, are of use for applications including drug delivery as the core can encapsulate hydrophilic, charged cargo. For such applications, it is essential to understand how the polymer architecture can be used to tune the size of these micelles. Using a model that captures the essential physics coupled with computational methods, we probe how the core size, corona size, and aggregation number. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C52.00005: Salt-concentration-dependent structure of Complex Coacervate Core Micelles Taeyoung Heo, SooHyung Choi Complex coacervation is a liquid-liquid phase separation when two oppositely charged polyelectrolytes are mixed in an aqueous solution. Because of the nature of electrostatic interaction, the coacervates are highly responsive to solution condition such as ionic strength. In this study, complex coacervate core micelles (C3Ms) are formed by simple mixing of AB and A’B diblock copolyelectrolyte solutions in an aqueous solution where A and A’ are oppositely charged blocks, and B is PEO block. Since the cores are coacervates, the C3Ms are also highly responsive to salt concentration. We investigate the salt-concentration-dependent structure of C3Ms with various molecular weight of charged block using dynamic light scattering (DLS) and small-angle X-ray/Neutron scattering (SAX/NS). As salt concentration increases, the aggregation number and core radii of C3M decrease. This reflects that the interfacial area per chain increases due to reduced interfacial tension between cores and solvent at higher salt concentration. In addition, salt resistance of C3Ms becomes stronger as the molecular weight is larger. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C52.00006: Structural Evolution and Formation Kinetics of Polyelectrolyte Complex Micelles Hao Wu, Jeffrey Ting, Matthew Tirrell Polyelectrolyte complex (PEC) micelles form when oppositely charged block polyelectrolytes are mixed together in aqueous media. The polyelectrolyte blocks, driven by electrostatic interaction, associate and phase separate, leading to a dense, polymer-rich PEC core stabilized by a neutral block corona. These nanoscale PEC micelles have various biomedical applications including RNA therapeutic delivery, tissue engineering, and diagnostics. The formation kinetics of PEC micelles, however, remains unknown. We employ time-resolved SAXS to investigate the formation kinetics of PEC micelles and the effects of various parameters on the growth rate. We focus on a model polyelectrolyte system that we have expertise in synthesis and has been extensively studied: poly(ethylene oxide)-block-poly(vinyl benzyl trimethyl ammonium chloride) (PEO-b-PVBTMA) complexed with either poly(ethylene oxide)-block-poly(styrene sulfonate sodium) (PEO-b-PSSNa) or poly(acrylic acid sodium) PAANa. Achieving a nanoscale description of the growth kinetics via TR-SAXS experiments will contribute towards enhancing our understanding of the complexation-driven assembly processes, and allow better design of polyelectrolyte complex based materials for biomedical applications. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C52.00007: Dynamics of liquid coacervates formed by oppositely charged polyelectrolytes Christian Aponte-Rivera, Michael Rubinstein Mixtures of oppositely charged polyelectrolytes can undergo a phase separation to form a polymer rich phase, called a coacervate, and a polymer depleted phase. The polymer rich phase can be a soft, viscous liquid, or a solid complex. Both types have drawn much attention in the literature due to their technological applications as well as their role in biological systems. Models have been developed to predict thermodynamic properties of the coacervates. However, much less attention has been given to modeling coacervate dynamics. We develop a scaling theory to predict the dynamics of entangled and unentangled asymmetric liquid coacervates formed from oppositely charged polyelectrolytes. The theory predicts the scaling of properties such as the relaxation modulus and shear viscosity of the coacervate, and the diffusivity of the polyelectrolyte chains. The scaling theory highlights the different dynamic regimes of the system, and how the dynamic properties can be tuned by experimentally controllable parameters such as the degree of polymerization or the number density of charges along the polyelectrolyte backbone, providing a means with which to rationally design dynamic properties for technological applications. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C52.00008: Polymer chemistry and effect on the linear viscoelasticity on polyelectrolyte complexes Yalin Liu, Cristiam F. Santa Chalarca, Rebecca A. Olson, Richard N. Carmean, Todd Emrick, Brent Sumerlin, Sarah Perry Polyelectrolyte complexes are formed through the electrostatic interaction of oppositely charged polymers. Depending the identity of salt, polyelectrolyte complexes can result in both solid precipitates and/or a liquid-liquid phase separation known as complex coacervation. The material properties can also change based on variations in the polymer chemistry, and the complex interplay between electrostatic interactions and water structure, controlled by salt. We tested three different polymer systems over a range of polymer chain lengths and salt conditions to understand how variations in polymer chemistry affect the thermodynamic phase behavior and the resulting material dynamics. The linear viscoelasticity of each polymer system was investigated under different salt conditions to enable a time-salt superposition and facilitate a broader characterization of the stress relaxation behavior. We compare differences in the slope of the horizontal shift factors as a function of salt concentration, which can be related to the activation energy barrier for the rearrangement of ionic interactions between polymers. The goal of this systematic study is to establish a general understanding of how molecular-level parameters can be used to tune the phase behavior and viscoelastic properties. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C52.00009: Ionic-group-dependent phase behavior of polyelectrolyte coacervates Sojeong Kim, SooHyung Choi, Won Bo Lee Complex coacervates are polymer-rich phases of liquid-liquid phase separation when two oppositely charged polyelectrolytes are mixed in aqueous solutions. Previously, Voorn-Overbeek model(VO model), simple and intuitive combination of the entropy of mixing and electrostatic interaction, was proposed to capture the behavior of complex coacervates. Since the VO model doesn't account for the chain connectivity of polyelectrolytes and chemistry-specific details, advanced models have been suggested up to now. However, experimental data of model system is rare to compare with the theoretical description. In this study, 4 polyelectrolytes are prepared (e.g.,strong/weak and polyanion/cation)and thus 4 pairs of polyelectrolyte complex coacervates are investigated to map out the phase diagrams as a function of the pair of the ionic group. It is found that the phase diagram shows distinctive features including (1)the salt resistance and the area of two-phase region are significantly dependent on the pairs of polyelectrolytes, and (2)the tie lines in the binodal curve show negative slope. We believe chemical-specific parameters play an important role to control phase behavior, and this observation shed a new light on the fascinating and biologically important topic of complex coacervation. |
Monday, March 4, 2019 4:18PM - 4:54PM |
C52.00010: Phase behavior and transport in solutions of oppositely charged polyelectrolytes Invited Speaker: Ronald Larson We develop a modeling framework for phase behavior and transport of oppositely charged polyelectrolytes (PE) in coacervates and Layer-by-Layer (LbL) assemblies that accounts for diffusion of both oppositely charged chains and their complexation. The core of the phase behavior model is the development of a free energy model that includes free energies for ion pairing, counterion condensation, charge regulation, electrostatic free energy, as well as elastic energy of the network and Flory Huggins entropy and enthalpy. We quantify a very strong influence of ion pairing and counterion condensation on phase behavior, and on the distribution of salt and polyelectrolyte species between the coacervate and supernatant phases, and find consistency of predictions with experimental data. From this free energy model, and an extended Stefan-Maxwell flux law based on the Doi-Onuki Rayleighian approach, the transport of PE chains, salts, and waters through polyelectrolyte LbL films are modeled, including the effects of chemical and electrostatic potentials, as well as mechanic stresses. The result is a unified approach that connects phase behavior to transport in polyelectrolyte assemblies, and may eventually allow rates of Layer-by-Layer assembly to be inferred from measurements of phase behavior and rheology. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C52.00011: Teaching a New Dog Old Tricks: Phase Inversion in Polyelectrolytes David Delgado, Kazi Sadman, Qifeng Wang, Kenneth R Shull While the design and synthesis of water filters has been the focus of a significant amount of research, there is still a need for easily processable and versatile materials for membrane fabrication. One such available materials system is based on polyelectrolyte complexes. In these complexes, polyanions and polycations form electrostatic rather than covalent bonds that are stable in most solvents. Current polyelectrolyte processing techniques such as layer by layer deposition are not scalable for industrial applications. In this work, a rapid quenching method induces a bi-phase separation within these complexes forming a desired porous structure much faster than current techniques. Additionally, simple changes in the processing chemistry allow for these membranes to be used in a wide suite of applications. Cross-sectional SEM was used to understand the driving factors behind pore formation. Furthermore, solvent stability measurements were taken using the quartz crystal microbalance. Finally, performance characteristics in a range of filtration were assessed. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C52.00012: Stretchable Ionic Double Layer at the Interface Between Crosslinked Networks of Ionic Liquids Hyeong Jun Kim, Baohong Chen, Zhigang Suo, Ryan Hayward Polymerized ionic liquids (PILs) are an emerging class of ion conducting materials wherein one of the ionic moieties in the ionic liquids is covalently attached to a polymer backbone. Crosslinked networks of ionic liquids (NILs) allows solid-state electrolyte that can selective conduct single ions. Herein, two oppositely charged NILs were prepared based on 1-ethyl-3-methyl imidazolium (3-sulfopropyl) acrylate ([ES]) and (1–(2–acryloyloxy–ethyl)–3–buthyl–imidazolium bis(trifluoromethane) sulfonimides ([AT]). At the interface of [ES]/[AT], we show that an ‘ionic double layer’ (IDL) is formed. The mobile ions are diffused away from the interfacial region, resulting in a build-up of excess fixed charges with a capacitance of ~ 1 mF/cm2. This IDL leads to asymmetric current flow when the polarity of the bias voltage is altered, analogous to the electrical rectification of a semiconductor diode. Moreover, the elastic properties of NILs allow a physical deformation which provides an electrical response that can be used for strain sensing or energy harvesting without the need for an external bias voltage. Our finding serves as a fundamentally new platform for a liquid-free, elastic and stretchable ionic diode that can harvest ambient mechanical energy such as human motion |
Monday, March 4, 2019 5:18PM - 5:30PM |
C52.00013: Complexation and network formation in a suspension of oppositely charged cellulose nanocrystals and poly(allylamine) Arkadii Arinstein, Patrick Martin, Gleb Vasilyev, Mor Boaz, Guang Chu, Eyal Zussman The structure formation, determined by tunable electrostatic interactions, in systems consisting of negatively charged cellulose nanocrystals (CNC) and a positively charged flexible weak polyelectrolyte, poly(allylamine) (PAAm), is discussed. Water dispersions, contained 3 wt.% CNC and 0.0364 wt.% PAAm of high molecular weight (65 kDa) that corresponds to the ionizable group stoichiometric ratio of system components, were examined. Variation in the dispersion pH allowed controlling the PAAm and CNC ionization level and hence the electrostatic interactions of the system constituents. For samples with high charge density, steady state viscosity measurements demonstrated cluster formation which consist of several CNC rods connected (due to ionic coupling) by PAAm tie macromolecules. Under certain conditions, these clusters (micro-gels) start to grow, merge and finally form a global network providing system elasticity. Oscillatory shear deformation experiments revealed a strong dependence of the storage and loss moduli on the PAAm ionization level. For high ionization degree of the system components, a strong network was formed but only after sonication, i.e. as a result of an activation; whereas for a low PAAm ionization level, the formed network was weak but required no activation. |
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