Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B52: Polyelectrolyte Complexation I: Coacervates and MoreFocus
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Sponsoring Units: DPOLY DBIO Chair: Debra Audus, National Institute of Standards and Technology Room: BCEC 253B |
Monday, March 4, 2019 11:15AM - 11:27AM |
B52.00001: Complexation of homologous polyions with variable polarity Jian Qin, Sean Friedowitz, Junzhe Lou, Yan Xia Polyelectrolyte complexation is sensitive to both long-ranged electrostatic interaction and short-ranged effects including solvation and ion association. We synthesized polyanions and polycations with identical backbone, variable length, and controlled solvation environment around charges. Systematic dependences on molecular weight and local environment are revealed by accurate polymer compositions determined using spectroscopic measurements, for nine sets of polymer pairs. Using two fitting parameters, the backbone solubility parameter and the ion-binding strength, the results are quantatively described by a solution free energy model that incorporates properly charge connectivity and ion-binding equilibrium. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B52.00002: Non-stoichiometric Coacervation between Hyaluronic Acid and Chitosan Basak Kayitmazer, Alaaddin Faruk Koksal, Elif Kilic Iyilik, Ozge Karabiyik Acar, Gamze Kose Hyaluronic acid and chitosan present a unique non-cognate pair where both polyelectrolytes are semi-flexible and have pH-dependent charges. These oppositely charged polysaccharides go into liquid-liquid phase separation far away from zero-zeta potential, which usually takes place at 1:1 charge ratios for other oppositely charged macroion-pairs. In this presentation, we explore the reasons behind non-stoichiometric coacervation for the HA/CHI pair. We also briefly studied effect of counterions on the coacervation window; i.e. extend of charge ratios where coacervation prevailed. If the counterion was present as a small ion of the solvent solution (Na+ or Ca+2), then its chaotropic nature had an effect of keeping the polymer hydrated despite the tendency to release the water molecules upon association of the polymers. This effect was enhanced when the polyelectrolyte had glutamate instead of chloride as its counterion. Since glutamate was a large zwitterion where the charge was distributed around different atoms, it served to extend the coacervation window. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B52.00003: Lower critical solution temperature in polyelectrolyte complex coacervates Vivek Prabhu, Samim Ali, Markus Bleuel Measurements on a common linear oppositely-charged polyelectrolyte complex system, potassium-poly(styrene sulfonate) and poly(diallyl dimethyl ammonium bromide), shows liquid-liquid phase separation upon heating, or lower critical solution temperature behavior. The experimental accessibility of the critical temperature occurs for a narrow range of monovalent salt concentration (Cs) with coexistence curves narrowing with increasing Cs that reduces the polymer concentration (Cp) in the polymer-rich phase. We will describe a qualitative comparison of this phase behavior to available mean field models. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B52.00004: Coacervate-driven self-assembly with Transfer Matrix Theory and Self-Consistent Field Theory Gary Min Chiang Ong, Charles Sing Complex coacervation occurs when two oppositely charged polyelectrolytes phase separate in an aqueous salt solution, resulting in a polymer dense coacervate phase and a polymer-dilute supernatant phase. Block copolyelectrolytes, which consists of both charged and neutral blocks, use this driving force to self-assemble into geometries which include micelles, vesicles and hexagonal rods. Coacervate-based materials provide advantages in (for example) the delivery of biologic materials, as encapsulation can be performed in the absence of organic solvent while maintaining stability of proteins. Recent advances in coacervation theory and simulations are used to understand the thermodynamics of coacervation-driven self-assembly. Transfer matrix theory is incorporated into self-consistent field theory (SCFT) to study how parameters like salt concentration, total polymer concentration and charge fraction of block copolyelectrolyes can affect the phase behavior of assembled structures, which is crucial in assisting in the design of materials. We show assembly that is analogous to uncharged block copolymer assembly in solution, and limits to standard coacervate phase behavior in the limit of long charged blocks. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B52.00005: Structure and rheology of polyelectrolytes in length-mismatched coacervates Amanda Marciel, Matthew Tirrell Polyelectrolyte complexes are highly tunable materials that span from low-viscosity liquids (coacervates) to high-modulus solids with high water content, making them attractive as surface coating, membrane purification and bioadhesive materials. However, most of their properties and their effects with salt, pH, polymer ratio and temperature have only been qualitatively described. Here, we present an investigation of the structure and chain conformations, and rheological properties of polyelectrolyte complex (PEC) coacervates comprising biomimetic model polyelectrolytes with mismatched lengths. This model system allows the chain length (6 – 800-mer), side-chain functionality and chirality (L, D) to be tuned while keeping the backbone chemistry constant, thus enabling a systematic investigation of polyelectrolyte chain conformation in the liquid coacervate phase. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B52.00006: Electrostatic Correlations: From Debye-Huckel Ionic Atmospheres to Counterion Condensation Kevin Shen, Zhen-Gang Wang We study electrostatic correlations by quantifying the relative contributions of linear-response ionic atmospheres (as first described by Debye and Huckel) and counterion condensation (CC). Even for aqueous solutions of highly charged polyelectrolytes, CC may contribute less than half of the (electrostatic) osmotic coefficient drop. We further show that after CC sets in, its relative contribution to the osmotic coefficient actually decreases with increasing concentration. We quantify the strength of CC in terms of an electrostatic binding constant that captures both direct interactions between condensing charges as well as non-local effects of screening and chain connectivity. Using this binding constant we elucidate the (anti)-cooperative nature of CC and the importance of chain conformations. Critically, we retain the discrete nature of the polyelectrolyte backbone and counterions -- this preserves "residual" electrostatic fluctuations of condensed charge pairs. Depending on the strength of residual charge fluctuations, CC can either stabilize or destabilize polyelectrolyte solutions against phase separation. |
Monday, March 4, 2019 12:27PM - 1:03PM |
B52.00007: Structure and Dynamics of Coacervates Formed by Oppositely Charged Polyelectrolytes Invited Speaker: Michael Rubinstein We develop a scaling theory and perform molecular dynamic simulations of weakly interacting coacervates with electrostatic interaction energy per charge less than thermal energy kT. Such liquid coacervates formed by oppositely charged polyelectrolytes can be asymmetric in charge density and number of charges per chain. We predict that these coacervates form interpenetrating solutions with two correlation lengths and two qualitatively different types of conformations of polyelectrolytes with lower and higher charge densities, which are analogous to chain conformations in quasi-neutral and in polyelectrolyte solutions, respectively. Weaker charged chains are attracted to and adsorbed on stronger charged chains forming a screening “coat” around the stronger charged polyelectrolytes. We present scaling prediction for polymeric diffusion coefficient, viscosity and stress relaxation function of these coacervates. Salt added at lower concentrations screens the repulsion between stronger charged chains, thereby reducing the thickness of the screening coat and resulting in the non-zero net polymer charge in the coacervate. At higher salt concentrations salt screens the attraction between oppositely charged chains, decreasing the coacervate concentration and its polymeric charge density. Thus, we predict a non-monotonic salt concentration dependence of polymeric charge density for asymmetric coacervates. Phase diagram for a mixture of oppositely charged polyelectrolytes at various compositions is proposed for different salt concentrations. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B52.00008: Complexation, Structure, and Rheology of Designer Polyelectrolytes Jeffrey Ting, Siqi Meng, Lu Li, Hao Wu, Amanda Marciel, Matthew Tirrell Polyelectrolyte complexes that form solid-like precipitates in water strongly resemble kinetically trapped solid mixtures and present formidable challenges in reproducing reliable properties and functionality. However, salt can be employed to break intermolecular ion pairs and process these nonequilibrium assemblies from a rubbery to a viscous liquid-like state. Here, we explore this transition with a pairing of RAFT-derived poly(styrene sulfonate sodium) (PSS) and poly(vinyl benzyl trimethylammonium chloride) (PVBTMA), using a combination of rheology, small angle X-ray scattering (SAXS), optical imaging, and thermal characterization. PSS and PVBTMA homopolyelectrolytes were synthesized at different molar masses with low dispersity; sodium bromide was chosen to probe individual chain and complex features. With no added salt, solid-like aggregates precipitated from solution. At 2.5 M salt, viscoelastic behavior was observed – shifting of the storage/loss moduli exhibited excellent time-salt superposition. Systematic SAXS studies were in good agreement with morphologies at various combinations of molar mass and salt. Finally, thermogravimetric analysis of the separate complex and supernatant phases enabled us to quantify the partitioning of salt and water. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B52.00009: Guanidinium can Break and Form Strongly Associating Ion-Complexes Kazi Sadman, Qifeng Wang, Kenneth R Shull Guanidinium is one of nature's strongest denaturants and is also a motif that appears in several interfacial contexts such as the RGD sequence involved in cell adhesion, cell penetrating peptides, and anti-microbial molecules. It is important to quantify the origin of guanidinium’s ion-specific interactions, so that its unique behavior may be exploited in synthetic applications. Here we show that guanidinium ions can both break and form strongly associating ion-complexes in a context-dependent way. These insights into guanidinium's behavior are elucidated using polyelectrolyte complexes (PECs), where inter-polymer ion-pairs between oppositely charged polymers play an important role in determining material stability. We demonstrate that guanidinium salts are very effective in dissolving the poly(styrenesulfonate)/poly(allylamine) (PSS:PAH) complex, which has one of the highest measured polycation-polyanion association affinities. We also demonstrate that incorporating guanidinium charges directly into the polyelectrolyte results in a complex that remains stable under highly denaturing conditions. The model system of PSS:PAH is used to glean insights into guanidinium's denaturing activity, and to broadly comment on the nature of ion-specific interactions in charged macromolecules. |
(Author Not Attending)
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B52.00010: Thermodynamic Characterization of Complex Coacervates of Oppositely Charged Biopolymers Fatma Akcay Ogur, Fatma Ahu Akin, Nayra Kavafyan, Busra Gun, Basak Kayitmazer
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Monday, March 4, 2019 1:39PM - 1:51PM |
B52.00011: The free energy profile of complexation of two oppositely charged polyelectrolyte chains Soumik Mitra, Arindam Kundagrami We report a study of the complexation process of two oppositely charged polyelectrolyte (PE) chains in dilute solution interacting through an attractive screened Coulomb potential. The system is modeled using the PE chain free energy within the uniform spherical expansion approximation where the two PE chains as well as the neutral complex are considered to be hypothetical spheres whose radii quantitatively denote the sizes of the respective chains. The two chains start overlapping due to attraction between the monomers, as well as the entropy gain of free counterions. The complexation process ends up in the formation of a neutral coecervate through mutual adsorption of oppositely charged monomers, with associated release of all counterions of both types. The free energy profile that follows this pathway is studied by obtaining the variations of the total free energy, as well as the various individual energy and entropy contributions, as functions of the extent of overlap of the two chains. Also the behavior of the chain size and charge as functions of overlap is presented. These results elucidate the competition of the various driving forces, both enthalpic and entropic in nature, which lead to complexation. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B52.00012: Confined Impingement Jet Mixing of Charged Polymers for Functional Structured Colloids and Encapsulation Douglas Scott, Robert K Prud'homme, Rodney Priestley Confined impingement jet (CIJ) mixing has been demonstrated as a scalable continuous process, thus enabling the mass production of structured nanocolloids consisting of distinct polymer domains as well as the encapsulation of sensitive active ingredients (SAIs) via the technique of flash nanoprecipitation (FNP). Due to the fast mixing in a CIJ mixer, competing timescales of mixing and aggregation dictate final particle size and morphology. Yet, incorporating charged polymers (e.g., ionomers and polyelectrolytes) and their additional timescales of electrostatic interactions has yet to be characterized in detail as a pathway for fabricating functional colloids. Here, we explore the impact of hydrophobic ionomers on traditional FNP for forming complex nanocolloids for use as amphiphilic colloidal surfactants in emulsification studies. The use of ionomers for stabilization of SAIs in a non-traditional medium is also presented. Additionally, the nascent technique of flash nanocomplexation (FNC) is developed as a scalable route for generating polyelectrolyte complexes where process parameters of charge ratio, charge density, and molecular weight disparity are explored in the context of fast mixing times. The application of FNC to the sustainable encapsulation of SAIs is demonstrated. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B52.00013: Gradient Nanoporous Poly(ionic liquid) Complex Membrane as Soft Actuators Jiayin Yuan This talk deals with nanoporous polyelectrolyte complex membranes by using poly(ionic liquid)s (PILs).1 PILs are the polymerization products of ionic liquids (ILs) and combine some properties and functions of ILs with polymers. We exploited PILs in the fabrication of nanoporous membranes via electrostatic complexation of PILs with polyacids.2 The porous structure results from phase separation of a hydrophobic PIL in water accompanied by ionic crosslinking between PIL and polyacids. The nanoporous membrane carries a gradient profile in the cross-linking density along the cross-section, triggered by the diffusive penetration of ammonia into the PIL-polyacid blend film. The membrane pore size is tunable from nano- to micrometer scale. The membrane features high actuation speed in response to acetone vapor and serves as environmental sensors to detect solvent quality.3,4 |
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