Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A31: Polyelectrolyte Complexation I: Phase BehaviorFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Svetlana Morozova, Case Western Reserve Univesrity Room: McCormick Place W-192A |
Monday, March 14, 2022 8:00AM - 8:36AM |
A31.00001: Complexation of Charged Polymers: From Coacervates to Polymeric Ionic Liquids and Plastic Waste Invited Speaker: Glenn H Fredrickson This talk will discuss the basic physics of charge complexation in polymers, leading for example to complex coacervation in aqueous mixtures of oppositely charged polyelectrolytes and self-coacervation of polyampholyte solutions. In the dry state, electrostatically-induced microphase separation is predicted when blending oppositely charged polymeric ionic liquids. The symmetry and domain period of such mesostructures are tunable by varying salt concentration, charge densities, stoichiometry, and dielectric contrast. I will discuss field theory models of such systems, and SCFT (mean-field) and FTS (exact) simulations that have elucidated some of their essential physics. Finally I will speculate on whether electrostatic interactions can be used to compatibilize and upcycle plastic waste streams. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A31.00002: Predicting polyelectrolyte complex coacervation from a molecularly-informed field-theoretic simulation approach My Nguyen, Nick Sherck, Kevin Shen, Brian Yoo, Stephan Kohler, Joshua Speros, Kris T Delaney, M. Scott Shell, Glenn H Fredrickson Understanding the phase behavior of polyelectrolyte coacervation is crucial for many applications, including a range of consumer products. However, in most cases, modeling coacervation is not easily accessible by molecular simulation methods due to the long-range nature of electrostatic forces and the typical high molecular weights of the species involved. We present a new simulation strategy to study complex coacervation leveraging the strengths of both particle and polymer field-theoretic simulations. Field theory is uniquely suited to capture larger length scales that are inaccessible to particle simulations, but its predictive capability is limited by the need to specify emergent (e.g. χ) parameters. Using model coacervate forming systems consisting of polyelectrolytes and/or surfactants, we show an original way to use small-scale, atomistic simulations to parameterize field theory models via the relative entropy coarse-graining approach. The capability of this approach is demonstrated by the prediction of the dependence of coacervation on important solution variables such as added salt and charged group composition. This synergistic approach opens the door to systematic design of a wide variety of polymeric formulations via simulations. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A31.00003: Polyelectrolyte Complex Coacervation across a Broad Range of Charge Densities Angelika S Neitzel Polyelectrolyte complex coacervates of homologous (co)polyelectrolytes with a near-ideally random distribution of a charged and neutral ethylene oxide comonomer were synthesized. The unique platform provided by these building blocks enabled an investigation of the phase behavior across charge fractions 0.10 ≤ f ≤ 1.0. Experimental phase diagrams for f = 0.30–1.0 were obtained from thermogravimetric analysis of complex and supernatant phases and contrasted with molecular dynamics simulations and theoretical scaling laws. At intermediate to high f, a dependence of polymer weight fraction in the salt-free coacervate phase (wP,c) of wP,c ∼ f0.37±0.01 was extracted; this trend was in good agreement with accompanying simulation predictions. Below f = 0.50, wP,c was found to decrease more dramatically, qualitatively in line with theory and simulations predicting an exponent of 2/3 at f ≤ 0.25. Preferential salt partitioning to either coacervate or supernatant was found to be dictated by the chemistry of the constituent (co)polyelectrolytes. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A31.00004: Transfer Matrix Model of of pH Effects in Polymeric Complex Coacervation Ashley R Knoerdel, Whitney C Blocher McTigue, Charles E Sing Oppositely-charged polyelectrolytes can undergo an associative phase separation driven by electrostatic attraction. This process is known as polymeric complex coacervation and leads to the formation of a polymer dense coacervate phase and a coexisting polymer-dilute supernatant phase. Complex coacervates have uses in personal care products and as biomolecular encapsulants, applications that require a full understanding of the fundamental molecular physics of coacervation. We aim to reconcile a notable difference between most experiments and theoretical models. Experiments often use weak polyelectrolytes whose charge state depends on solution pH, while theoretical models typically assume strong polyelectrolytes. There have only been a few models to try to account for pH effects on complex coacervation. We modify the transfer matrix theory of coacervation to account for pH effects. We demonstrate that asymmetric phase diagrams can exist when charge stoichiometry is not equal, leading to a partitioning of one salt species into the coacervate phase to maintain electroneutrality which can suppress phase separation. We also demonstrate that mixtures off-stoichiometric in volume fraction but stoichiometric in charge have the greatest propensity to form coacervate phases. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A31.00005: Polyelectrolyte complex coacervation in solvent mixtures Yuanchi Ma, Jan Obrzut, Jack F Douglas, Vivek M Prabhu A lower critical solution temperature (LCST) behavior was recently observed in the polyelectrolyte complex coacervation of stoichiometric mixtures in potassium poly(styrene sulfonate) (KPSS) and poly(diallyldimethylammonium bromide) (PDADMAB) in water with added KBr salt. Many features are explained by an interplay of entropy of mixing, electrostatic correlations, and solvent quality arguments. While the electrostatic correlations are quantified by magnitude of the Bjerrum length, the temperature dependence of the dielectric constant of water must be considered. However, alternate solvents should also independently tune the Bjerrum length (via the dielectric constant) beyond that achieved with water. We will show experimental measurements of the effects of solvent mixtures on the coacervation behavior of KPSS/PDADMAB through a combination of static and dynamic light scattering, turbidity, and measurements of the static dielectric constant. We identify regimes where solvent quality (hydrophobicity) become a predominant factor in coacervation. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A31.00006: Pathway and Driving Force in Polyelectrolyte Complex Coacervation Shensheng Chen, Zhen-Gang Wang Polyelectrolyte complex coacervation is a liquid–liquid phase separation when mixing a polycation solution with a polyanion solution. There has been extensive research on this problem in recent years due to its fundamental role in biology and in materials and biomedical applications. However, little is known about the pathway for the coacervate from the dilute phase, and there is considerable controversy regarding the thermodynamic driving force. Theory and simulation have suggested that the polycations and polyanions exist as pairs in the supernatant phase. Here, using umbrella sampling, we perform MD simulations to study the potential of mean force (PMF) between two pairs of polycation and polyanion in dilute solution. Our result shows that the merging of the two pairs is slightly dominated by energy in salt-free condition, and becomes entropy-driven in the presence of added salts. We further estimate the polymer concentration in the dilute phase from the calculated PMF. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A31.00007: Stabilization of polyelectrolyte complexes via cation-π interactions Jennifer E Laaser, Jun Huang, Lexi R Knight We investigate the impact of cation-π and π-π interactions on the phase behavior and thermodynamics of polyelectrolyte complexation in a series of well-defined polyelectrolytes with aromatic (benzyl) and non-aromatic (cyclohexanemethyl) sidechains. The phase behavior of the complexes is quantified using optical turbidity in the presence of salts with different expected cation-π interaction strengths. We find that for the non-aromatic polymers, the measured salt resistances are independent of salt choice. For the aromatic polymers, on the other hand, the salt resistance increases as the salt is changed from KCl to NaCl to LiCl, reflecting decreasing ability of the inorganic salt to compete with and break apart inter-chain cation-π interactions. The thermodynamics driving this behavior are further quantified via isothermal titration calorimetry, and reveal that the enthalpy of complexation is significantly higher in the aromatic systems with weakly interacting salts. These results suggest that cation-π interactions can be an important driver of polyelectrolyte complexation, and should be accounted for when analyzing and interpreting complexation experiments on other aromatic polyelectrolytes. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A31.00008: Water-, salt-, and temperature-induced phase transitions in polyelectrolyte complexes Chikaodinaka I Eneh, Jodie Lutkenhaus Oppositely charged polyelectrolytes may experience a solid-liquid (precipitate) or liquid-liquid (coacervate) phase separation upon aqueous assembly. This phase separation is influenced by polymer properties such as molecular weight and charge density, solvent properties such as pH and ionic strength, and environmental properties such as temperature and humidity. Understanding polyelectrolyte complexes is valuable for advancing drug delivery systems, underwater adhesives, and multi-compartment cells. Many theories define the coacervate-solution phase boundary exist, but a gap in the knowledge of the coacervate-precipitate boundary remains. In this study, using turbidity, conductivity measurements, thermogravimetric analysis (TGA), and optical microscopy (OM), we identify the phase boundaries of poly(diallyldimethyl ammonium)/poly(acrylic acid) complexes. We observe reversible temperature-induced phase transitions using OM and quantify the water content in both macro- and micro-phase separated coacervates as a function of temperature and salt. These results provide more understanding of salt, water, and polymer contributions to phase transitions. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A31.00009: Charged Complexes of Random Copolymers for Applications in Environmental Sustainability Jeremy Wang, Curt Waltmann, Han Umana-Kossio, Carolyn E Mills, Danielle Tullman-Ercek, John M Torkelson, Monica Olvera De La Cruz
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Monday, March 14, 2022 10:12AM - 10:24AM |
A31.00010: Scattering Function in Systems of Charged Polymers: From Polyelectrolyte Solutions to Polyelectrolyte Complexes Yuan Tian, Ryan Sayko, Heyi Liang, Andrey V Dobrynin The peak in the scattering function, appearing at intermediate length scales, is a unique feature of solutions of charged polymers. To elucidate the effect of counterion valence (degree of polymerization of neutralizing chains) on the peak position and the form of the scattering function, we use a combination of coarse-grained molecular dynamics simulations and analytical calculations in the framework of the Random Phase Approximation (RPA). Both simulations and RPA calculations show that the peak location q* in the structure factor S(q) moves towards smaller q values with decreasing solution concentration. In particular, we find that q* scales with concentration as ρ-0.25. Furthermore, we demonstrate that the plateau in S(q) at small q is controlled by the system compressibility and increases with increasing degree of polymerization of polymeric counterions. The observed changes in the shape of the structure factor S(q) obtained from simulations can be fit by a scattering function derived in the framework of RPA by considering a solution of neutral chains as a reference system. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A31.00011: Interlude of Mesomorphic State in Polyelectrolyte Complexation Di Jia, Murugappan Muthukumar Liquid-liquid phase separation of a solution of oppositely charged macromolecules into precipitation upon a decrease in concentration of added salt is well known. Here, using light scattering studies on complexation in aqueous solutions of polycations and oppositely charged organic salt, we report an unusual phenomenon of the emergence of a mesomorphic state. This state occurs with well-defined self-assembled structures in between the homogeneous solution and precipitation as the salt concentration is progressively decreased. Using systematic variations in the concentration c_p and molecular weight of the polymers, charge ratio between the two species, and salt concentration, the mesomorphic state is quantified. For the example of poly(L-lysine) bromide and sodium acrylate, the linear size R of self-assembled structures obeys the universal law of proportionality between R and c_p^(1/6). The mesomorphic state is flanked by precipitation at lower ionic strengths and homogeneous phase at higher ionic strengths. Furthermore, the mesomorphic state disappears by self-poisoning upon increasing polymer concentration at fixed charge ratio. These novel results are interpreted using dipolar interactions and Debye screening. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A31.00012: Role of entropy in charged polymers and its complexes Soumik Mitra, Arindam Kundagrami The thermodynamics of charged polymer systems is characterized by the interaction potentials and entropy of the connected monomers and free counterions respectively. We review the role of entropy in several charged polymer systems. From single polyelctrolyte(PE) chain to PE networks it is seen that the ideal gas entropy of free counterions and the configurational entropy of polymers play important roles in determining the equilibrium structure of the PEs. The pressure due to confined counterions is important in dictating the kinetics of conformational changes in single PE chain. In PE gels, the free ion entropy lurks beneath the mixing entropy to characterize its swollen state in solution. A system of two oppositely charged interacting polyelectrolytes identify the strong role played by the free counterion entropy in complex formation and shows its dependence on the ambient conditions, like temperature and salt concentration. Though the bound ion pair enthalpy is an important entity in charged polymer systems, the complexation between two oppositely charged PE chains show a large release of counterions from the respective chains, resulting in a large entropy gain which drives the process. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A31.00013: Monovalent salt induced simple coacervation of guanidinium-functionalized polyelectrolytes Seunghwan Oh, Jinhoon Lee, Minhwan Lee, Seulwoo Kim, Wonbo Lee, Dongwoog Lee, SooHyung Choi Liquid-liquid phase separation (LLPS) is frequently induced by the non-covalent intermolecular associations such as electrostatic, π-π, cation-π, and hydrophobic interactions, which is actively observed in biological system. Recently, an arginine residue containing a flat and positively charged guanidinium functional group is of great interest due to the distinct amphiphilicity and strong interaction. Herein, the salt-induced LLPS of guanidinium-functionalized polyelectrolytes is addressed. The polyether-based guanidinium functionalized poly(allyl glycidyl ether) (G-PAGE) was synthesized by anionic ring-opening polymerization and post-modification. We observed that the G-PAGE solution shows that LLPS occurs when the electrostatic repulsion is sufficiently reduced by adding monovalent salt, and the coacervates follows the upper critical solution temperature (UCST) behavior. The larger and more polarizable monovalent anions screen the electrostatic repulsion more efficiently by counterion adsorption. Our finding suggests that that the π-π stacking between guanidinium groups is strong and crucial to lead the LLPS of guanidinium-rich polyelectrolyte in biological contexts. |
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