Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R10: Polyelectrolyte Complexation |
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Sponsoring Units: DPOLY Chair: Debra Audus, NIST Room: 269 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R10.00001: Complex Coacervation of Oppositely Charged Polyelectrolyte Mixtures: a Liquid-State Theory Study Pengfei Zhang, Nayef Alsaifi, Jianzhong Wu, Zhen-Gang Wang Complex coacervation refers to a phase separation of oppositely charged polyelectrolyte (PE) mixtures into a PE-poor supernatant phase and a PE-rich coacervate phase. This phenomenon arises from the delicate interplay among the mixing entropy, excluded volume, chain connectivity, and electrostatic interactions. Using a simple liquid-state (LS) theory that accounts for all of these effects, we study the phase behaviors of a mixture of oppositely charged PE solutions. In comparison with the prediction from the well-known Voorn-Overbeek (VO) theory, the LS theory predicts a much narrower phase-separated region for the stoichiometric mixture. Moreover, the LS theory predicts that salt concentration is higher in the supernatant phase than the coacervated phase, opposite to the VO prediction. The effect of non-stoichiometry on the phase behavior is also studied in detail. In particular, we find two different regimes of mixing ratio with respect to the partition of excess PE chains in the coexisting phases for the mixture without extra salt: in the weakly asymmetric regime, nearly all of the excess PE-chain are distributed in the coacervate phase, while in the strongly asymmetric regime, most of the excess PE chains are accumulated in the supernatant phase. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R10.00002: Dynamics in Complex Coacervates Sarah Perry Understanding the dynamics of a material provides detailed information about the self-assembly, structure, and intermolecular interactions present in a material. While rheological methods have long been used for the characterization of complex coacervate-based materials, it remains a challenge to predict the dynamics for a new system of materials. Furthermore, most work reports only qualitative trends exist as to how parameters such as charge stoichiometry, ionic strength, and polymer chain length impact self-assembly and material dynamics, and there is little information on the effects of polymer architecture or the organization of charges within a polymer. We seek to link thermodynamic studies of coacervation phase behavior with material dynamics through a carefully-controlled, systematic study of coacervate linear viscoelasticity for different polymer chemistries. We couple various methods of characterizing the dynamics of polymer-based complex coacervates, including the time-salt superposition methods developed first by Spruijt and coworkers to establish a more mechanistic strategy for comparing the material dynamics and linear viscoelasticity of different systems. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R10.00003: Molecular Structure and Sequence in Complex Coacervates Charles Sing, Tyler Lytle, Jason Madinya, Mithun Radhakrishna Oppositely-charged polyelectrolytes in aqueous solution can undergo associative phase separation, in a process known as complex coacervation. This results in a polyelectrolyte-dense phase (coacervate) and polyelectrolyte-dilute phase (supernatant). There remain challenges in understanding this process, despite a long history in polymer physics. We use Monte Carlo simulation to demonstrate that molecular features (charge spacing, size) play a crucial role in governing the equilibrium in coacervates. We show how these molecular features give rise to strong monomer sequence effects, due to a combination of counterion condensation and correlation effects. We distinguish between structural and sequence-based correlations, which can be designed to tune the phase diagram of coacervation. Sequence effects further inform the physical understanding of coacervation, and provide the basis for new coacervation models that take monomer-level features into account. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R10.00004: Molecular Effects on Coacervate-Driven Block Copolymer Self Assembly Tyer Lytle, Mithun Radhakrishna, Charles Sing Two oppositely charged polymers can undergo associative phase separation in a salt solution in a process known as ‘complex coacervation.’ Recent work has used this as a motif to control the self-assembly behavior of a mixture of oppositely-charged block copolymers which form nanoscale structures. The materials formed from these complex coacervate-block copolymers (BCPs) have potential use as drug delivery systems, gels, and sensors. We have developed a hybrid Monte Carlo-Single Chain in a Mean Field (MC-SCMF) simulation method that is able to determine morphological phase diagrams for BCPs. This technique is an efficient way to calculate morphological phase diagrams and provides a clear link between molecular level features and self-assembly behaviors. Morphological phase diagrams showing the effects of polymer concentration, salt concentration, chain length, and charge-block fraction at large charge densities on self-assembly behavior have been determined. An unexpected phase transition from disorder to hexagonal packing at large salt concentrations has been observed for charge-block fractions equal to and larger than 0.5. This is attributed to the salt filling space stabilizing the morphology of the BCP. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R10.00005: Interaction between Oppositely Charged Polymers Anisha Shakya, John King When allowed to interact, oppositely charged polymers are known to form a variety of different phases ranging from soluble colloidal/nanoparticulate complexes, insoluble complexes, and liquid-like phase separated complex coacervates. The interactions in such complexes are of relevance to different fields such as industrial application of synthetic polyelectrolyte polymers, therapeutic nucleic acid delivery, and biology in order to understand formation and function of membrane-less organelles in cells. Owing to their polyanionic nature, nucleic acids can form complex phases with positively charged polymers. Using a combination of experimental techniques, we explore such complexes in order to understand their structural organization, complex microenvironments, internal dynamics, and their response to changing extrinsic environment. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R10.00006: Sequence effects on Polyelectrolyte Complexation Michael McGovern, David Morse, Kevin Dorfman The complexation of a polyelectrolyte with an oppositely charged micelle is an important problem, with particular applications in the formulation of materials such as gene delivery vehicles. The physical process driving complexation is complicated, involving both counter-ion release and redistribution of charge inside the micelle. Recent experiments indicate that both the thermodynamics and the dynamics of this process are affected by the charge sequence of the polyelectrolyte. Motivated by these experiments, we have performed molecular dynamics simulations on the complexation between free polyelectrolytes in solution and an oppositely charged polyelectrolyte brush, serving as a simple model for a micelle. One of the moieties is a polyelectrolyte with uniform change density and the other is a copolymer. We consider different types of copolymers (block, alternating) to address the effect of charge sequence. We will present results on the effects of sequence on chain mobility, the frequency of exchanges between bound and free polyelectrolytes, and the degree of overcharging of the complexes under different conditions of polyelectrolyte concentration and salt concentration. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R10.00007: Effects of charge connectivity on macromolecular complexation Jian Qin Mixing solutions of polycations and polyanions under favorable conditions results in the formation of a liquid-like polymer-rich complex phase known as coacervate. The coacervate typically coexists with a supernatant that is nearly depleted of polymers. The coexistence is conventionally rationalized by using the Voorn-Overbeek model, which treats the electrostatic correlation free energy at the Debye-H\"uckel level. A key physics missing from this model is charge connectivity. We model the charge connectivity by using the structure factor, couple it to the Gaussian theory for electrostatic correlation free energy, and show that the charge complexation is greatly enhanced. The degree of enhancement is quantified by the scaling exponent for the molecular weight dependence of the minimum charge density needed to induce complexation, which is shown to correlate strongly with the fractal dimension of macromolecules. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R10.00008: Effects of the dielectric contrast and hydrogen bond between polymer and ionic liquid on the shift in the critical point of the spinodal from a polymer-poor to a polymer-rich region Issei Nakamura We consider the dielectric contrast and hydrogen bond between the homopolymer and ionic liquid and the effect of fluctuations in the local density and electrostatic potential. Our coarse-grained mean-field theory shows that such an effect may rationalize the observed shift in the critical point and the asymmetry of the observed spinodal curve. The effect of the dielectric contrast between the polymer and the ionic liquid causes a significant shift in the critical point of the spinodal from a polymer-poor to a polymer-rich region. The fluctuation effect changes the trend of the phase boundary in a nonmonotonic manner. Hydrogen bonding also yields similar effects, but the spinodal curve rather exhibits a double-well structure or relatively flat structure when combined with the solvation energy of ions. We thus demonstrate that hydrogen bonding, ion solvation, and the fluctuation have equal significance on the magnitude and trend of the spinodal curve. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R10.00009: Effects of drying and ionic strength on non-linear growth of polyelectrolyte multilayers Victor Selin, John Ankner, Svetlana Sukhishvili We report on factors affecting the non-linear growth of electrostatically assembled polyelectrolyte multilayer (\textit{nl}PEM) films. The films were assembled by the layer-by-layer (LbL) technique using poly(methacrylic acid) as the polyanion and quaternized poly-2-(dimethylamino)ethyl methacrylate as the polycation. Evolution of the film thickness was systematically monitored during LbL multilayer formation, including both dry and \textit{in situ} measurements. Spectroscopic ellipsometry measurements of dry and wet film thicknesses indicated that \textit{nl}PEM films were highly swollen (2-4 fold). Moreover, the swelling ratio could be controlled by the application of a drying step after each deposition cycle, and enhanced by the presence of salt during \textit{nl}PEM assembly. Probing the film internal structure using neutron reflectometry showed that the \textit{nl}PEMs were interdiffused yet stratified. The degree of intermixing between neighboring layers can be controlled during film deposition. While the application of drying between layer deposition steps improved film stratification, the presence of 0.1-0.3 M NaCl resulted in more interdiffused films, with the interfacial widths exceeding the radius of gyration of the polymer chains. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R10.00010: Effect of Water on the Thermal Transition Observed in Polyelectrolyte Complexes Yanpu Zhang, Piotr Batys, Fei Li, Jodie Lutkenhaus, Maria Sammalkorpi Polyelectrolyte complexes (PECs), formed by the association of oppositely charged polyelectrolytes in solution, undergo a glass transition-like event of an unclear nature. This transition event has been detected using calorimetry or mechanical techniques. The observed thermal transition temperature (T$_{\mathrm{tr}})$ is influenced by both the complexation condition and subsequent addition of water. Recent simulation work suggests that water with the polyelectrolyte plays dual roles: weakening polyelectrolyte ion pairs and also undergoing a subtle dehydration process with increasing temperature. Here, we present the influence of water on two pairs of PECs, poly(diallyldimethylammonium chloride) $-$poly(sodium 4-styrenesulfonate) (PDAC$-$PSS), and poly(allylamine hydrochloride)$-$poly(acrylic acid) (PAH$-$PAA), in which the PEC structure and composition are affected by complexation conditions, NaCl concentration or pH values. Modulated differential scanning calorimetry (MDSC) reveals a T$_{\mathrm{tr}}$ that decreases in value with increasing hydration and decreasing polyelectrolyte-polyelectrolyte ion pairing. We show the collapse of all T$_{\mathrm{tr}}$ values into a single master curve when plotted against the ratio of water molecules per polyelectrolyte-polyelectrolyte ion pair. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R10.00011: Spontaneous formation of aqueous droplets in complex coacervate systems Samim Ali, Vivek Prabhu Complex coacervation occurs when a solution of two oppositely charged polymers undergoes liquid-liquid phase separation under suitable conditions. The coacervate forms the highly viscoelastic polymer-rich phase that exhibits very low interfacial tension with the polymer-poor supernatant. This presentation will describe the spontaneous formation of micron-sized aqueous droplets in the polymer-rich coacervate domain as the temperature of the system is increased above a critical value. The spherical droplets, initiated at the liquid-liquid interface, propagates into the bulk coacervate domain. Moreover, the average size of the droplets increases monotonically with increase in temperature. This results in an optically turbid appearance of the coacervate. We evaluate the role of liquid-liquid interface and polymer structure inside the coacervate phase during such transition using rheological techniques and small-angle neutron scattering. These observations provide a foundation to understand coacervate properties at conditions useful to encapsulation, delivery media, and wet adhesives. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R10.00012: Field Theoretic Simulations of Self-Coacervation Phenomena in Block Polyampholytes Scott Danielsen, Kris Delaney, Rachel Segalman, Glenn Fredrickson Polyelectrolyte complexation is a common phenomenon in natural polymers and has been applied to synthetic materials systems for coatings, adhesives, and encapsulants. Single-component polyelectrolyte complexes are formed when block polyampholytes exhibit self-coacervation, phase separating into a dense liquid coacervate phase rich in the polaympholyte coexisting with a dilute supernatant phase. Using fully fluctuating field theoretic simulations, we explore the phase behavior of block polyampholytes in solution to understand the structure and thermodynamics of the self-coacervate. Results are shown concerning the effects of block architecture, excluded volume, and explicit counterions on the phase diagram. Simple analytical and random phase approximation (RPA) expressions are used to discuss scaling relationships. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R10.00013: Stoichiometric Polyzwitterion-Inorganic Heterpolyaion Complexation into Tunable Coacervates and Hydrogels. Benxin Jing, Manuela Ferreira, Yingxi Elaine Zhu Complexation of polycations and polyanions into different condense phases has been much investigated, yet the mechanism behind the formation of liquid-like coacervates and solid/gel-like complexes remains debated. Instead of using two oppositely charged polyelectrolytes in salted aqueous solutions, we have successfully prepared a series of stoichiometric organic-inorganic macroion coacervates by using zwitterionic polysulfobetaine (PSBMA) and inorganic polyoxometalates (POMs) polyanions of similar atomic coordination structure but varied valence and charge density in LiCl solutions. Additionally, by tuning POM-to-PSBMA charge ratio, LiCl salt concentration, and temperature, reversible phase transition among homogeneous solution, biphasic liquid-like coacervation, and gel is observed. Measurements of electric potential of PSBMA upon PSBMA-POM coacervation suggest ion pairing formed between cation sites of PSBMA dipolar side groups and multivalent POM anions. The composition analysis by TGA and conductivity of supernatant solution also suggest that the entropy gain by releasing simple ions to solution due to the binding of POMs with PSBMA is responsible for the coacervate formation. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R10.00014: Polyelectrolyte Complexes in Solution: A Molecular Dynamics Study Yanfei Tang, Shengfeng Cheng Ion-containing polymers including polyelectrolytes are important materials in food, energy, and water industry. To better understand the morphology and fabrication of polyelectrolyte based materials, we employ molecular dynamics simulations to study the complexation of oppositely charged polyelectrolyte chains in solution. Our simulations show that the structure of the resulting complex formed by polyanions (PAs) and polycations (PCs) depends on the charge ratio ($x)$ between the PC and PA chains and salt concentration (\textit{Cs}). At $x$ near 1 and small \textit{Cs}, all chains condense into a macroscopic drop. This macroscopic drop phase exists only in a small range of \textit{Cs} and is destabilized when \textit{Cs} is increased beyond a certain $x$-dependent threshold. When $x$ is smaller than 1, the number of PC chains is insufficient to neutralize all PA chains. When $x$ is large than 1, one or several PA chains form fractal-like complexes with abundant PC chains. Our simulations suggest that the macroscopic drop phase become unstable when $x$ deviates from 1 in both negative and positive directions. [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R10.00015: Diffusion of oligonucleotides from within Iron-Cross-Linked, Polyelectrolyte-Modified Alginate Beads: A Model System for Drug Release. Sergii Domanskyi, Vladimir Privman, Roberto Luz, Nataliia Guz, Lawrence Glasser, Evgeny Katz An analytical model to describe diffusion of oligonucleotides from stable hydrogel beads is developed and experimentally verified. The synthesized alginate beads are Fe3$+$-cross-linked and polyelectrolyte-doped for uniformity and stability at physiological pH. Data on diffusion of oligonucleotides from inside the beads provide physical insights into the volume nature of the immobilization of a fraction of oligonucleotides due to polyelectrolyte cross-linking, that is, the absence of a surface layer barrier in this case. Furthermore, the results suggest a new simple approach to measuring the diffusion coefficient of mobile oligonucleotide molecules inside hydrogels. The considered alginate beads provide a model for a well-defined component in drug-release systems and for the oligonucleotide-release transduction steps in drug-delivering and biocomputing applications. This is illustrated by destabilizing the beads with citrate, which induces full oligonucleotide release with nondiffusional kinetics. [Preview Abstract] |
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