Polyelectrolyte Solutions Research Articles

Ion-specific effects in polyelectrolyte solutions: chain–chain interactions, chain rigidity and dynamics

Ion-specific effects in polyelectrolyte solutions: chain–chain interactions, chain rigidity and dynamics

Microfluidic purification of genomic DNA

We describe a microfluidic device to extract DNA from a cell lysate, without the need for centrifuges, magnetic beads, or gels. Instead, separation is driven by transverse migration of DNA, which occurs when a polyelectrolyte solution flowing through a microfluidic channel is subjected to an electric field. The coupling of the weak shearing with the axial electric field is highly selective for long, flexible, charged molecules, of which DNA is the sole example in a typical cell lysate. As a result of migration to the walls, DNA is held near the channel inlet by electrophoresis (there is no flow near the channel walls), while the remaining components are eluted by the much larger (at least 10-fold) convective flow. We have demonstrated the feasibility of the device by recovering up to 40 ng of purified DNA in less than 30 min from 10 μL of Escherichia coli lysate. Gel electrophoresis indicates minimal additional fragmentation during purification, up to the maximum length recorded by the gel (60 kbp). Electropherograms were also obtained for purified mammalian DNA, using a Femto Pulse system (fragment lengths up to 165 kbp). Extracted samples show strong amplification by PCR, while the original lysate does not. Mixtures of λ-DNA and BSA were used to determine the extent of the separation of DNA from a physiological concentration of proteins (30 mg/mL). The protein concentration in the extract (0.3 to 0.5 ng/µL) was reduced by five orders of magnitude from the initial mixture.

Self-Diffusion of Star and Linear Polyelectrolytes in Salt-Free and Salt Solutions.

This work explored solution properties of linear and star poly(methacrylic acids) with four, six, and eight arms (LPMAA, 4PMAA, PMAA, and 8PMAA, respectively) of matched molecular weights in a wide range of pH, salt, and polymer concentrations. Experimental measurements of self-diffusion were performed by fluorescence correlation spectroscopy (FCS), and the results were interpreted using the scaling theory of polyelectrolyte solutions. While all PMAAs were pH sensitive and showed an increase in hydrodynamic radius (R h) with pH in the dilute regime, the R h of star polymers (measured at basic pH values) was significantly smaller for the star polyacids due to their more compact structure. Fully ionized star PMAAs were also found to be less sensitive to changes in salt concentration and type of the counterion compared to linear PMAA. While R h of fully ionized linear PMAA decreased in the series Li+ > Na+ > K+ > Cs+ in agreement with the Hofmeister series, R h of star PMAAs was virtually independent of type of the counterion for eight-arm PMAA. However, molecular architecture strongly affected interactions of counterions with PMAAs. In particular, 7Li NMR revealed that the spin-lattice relaxation time T 1 of Li+ ions in low-salt solutions of eight-arm PMAA was ∼2-fold smaller than that in the solution of linear PMAA, suggesting slower Li+-ion dynamics within star polymers. An increase in concentration of monovalent chloride salts, c s, above that of the PMAA monomer unit concentration (c m) resulted in shrinking of both linear and star molecules, with the hydrodynamic size R h scaling as R h ∝ c s -0.11±0.01. Self-diffusion of linear and star polyelectrolytes was then studied in a wide range of polyelectrolyte concentrations (10-3 mol/L < c m < 0.5 mol/L) in low-salt (<10-4 mol/L of added salt) and high-salt (1 mol/L) solutions. In both the low-salt and high-salt regimes, diffusion coefficient D was lower for PMAAs with a larger number of arms at a fixed c m. In addition, in both cases, D plateaued at low polymer concentrations and decreased at higher polymer concentrations. However, while in the high-salt conditions, the concentration dependence of D reflected transitions between the dilute to semidilute solution regimes as expected for neutral chains in good and theta solvents, analysis of the diffusion data in the low-salt conditions using the scaling theory revealed a different origin of the concentration dependence of D. Specifically, in the low-salt solutions, both linear and star PMAAs exhibited unentangled (Rouse-like) dynamics in the entire range of polyelectrolyte concentrations.

Ion Activity Coefficient of Sodium Halides in Anion-Exchange Polymers: Empirical Model Based on Manning’s Counterion Condensation Theory

The theory of electrolyte solution provides a precise description of the thermodynamic state and non-ideality of electrolyte solutions, allowing for the accurate prediction of the crystallization separation process of Salt Lake brine. Analogously, we attempt to describe the non-ideality of ions in ion-exchange polymers based on Manning’s Counterion Condensation Theory, which was originally used to describe the thermodynamics of polyelectrolyte solutions, has amply proven the potential to extend to ion-exchange polymers. In this article, equilibrium solvent and solute concentrations in aminated cross-linked polystyrene AEM were determined experimentally as a function of external NaCl concentration, and ion activity coefficients in the membranes were obtained via a thermodynamic treatment. With the recombination and empirical parameters added to Manning’s model, the ion activity coefficient of NaCl and NaBr in the aminated cross-linked polystyrene AEM can be accurately described in concentration ranges of 0.01 mol·kg−1~3 mol·kg−1. Compared with the original model, the Coefficient of Determination between the improved model and the experimental data was increased from 0.65 to 0.95. The Residual Sum of Squares is reduced by about one order of magnitude, significantly improving the Manning model’s adaptability when applied to AEM.

Influence of Solvent Dielectric Constant on the Complex Coacervation Phase Behavior of Polymerized Ionic Liquids.

Complex coacervation is an associative phase separation process of oppositely charged polyelectrolyte solutions, resulting in a coacervate phase enriched with charged polymers and a polymer-lean phase. To date, studies on the phase behavior of complex coacervation have been largely restricted to aqueous systems with relatively high dielectric constants due to the limited solubility of most polyelectrolytes, hindering the exploration of the effects of electrostatic interactions from differences in solvent permittivity. Herein, we prepare two symmetric but oppositely charged polymerized ionic liquids (PILs), consisting of poly[1-[2-acryloyloxyethyl]-3-butylimidazolium bis(trifluoromethane)sulfonimide] (PAT) and poly[1-ethyl-3-methylimidazolium 3-[[[(trifluoromethyl)sulfonyl]amino]sulfonyl]propyl acrylate] (PEA). Due to the delocalized ionic charges and their chemical structure similarity, both PAT and PEA are soluble in various organic solvents with a wide range of dielectric constants, ranging from 16.7 (hexafluoro-2-propanol (HFIP)) to 66.1 (propylene carbonate (PC)). Notably, no significant correlation is observed between the solvent dielectric constant and the phase diagram of the complex coacervation of PILs. Most organic solvents lead to similar phase diagrams and salt resistances regardless of their dielectric constants, except two protic solvents (HFIP and 2,2,2-trifluoroethanol (TFE)) showing significantly low salt resistances compared to the others. The low salt resistance in these protic solvents primarily arises from strong hydrogen bonding between PILs and solvents as evidenced by 1H NMR and small-angle neutron scattering (SANS) experiments. Our finding suggests that for the coacervation of PILs, particularly those with delocalized and weak charge interactions, entropy from the counterion release and polymer-solvent interaction χ parameter play a more important role than the electrostatic interactions of charged molecules, rendered by the dielectric constant of the solvent medium.

Dynamic Surface Properties of Styrene and Hydrophobized 4-Vinylbenzyl Chloride Copolymers at the Air-Water Interface

The kinetic dependences of surface tension, dilatational dynamic surface elasticity and ellipsometric angles of solutions of copolymers of styrene and 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine, as well as the micromophology of adsorption and spread layers of this polyelectrolyte were determined. All kinetic dependences of the dynamic surface elasticity were found to be monotonic, in contrast to the results for previously studied polyelectrolyte solutions without polystyrene fragments. The peculiarities of surface properties of the studied solutions may be related to the formation of microaggregates in the surface layer, preventing the formation of loops and tails of polymer chains at the interfacial boundary, and, consequently, the decrease in surface elasticity after the local maximum. The occurrence of aggregates with sizes of 1–4 nm in the Z-direction in the surface layer is also indicated by atomic force microscopy data. The obtained results confirm the earlier conclusions about the formation of aggregates in the surface layer of polyelectrolyte solutions containing sodium polystyrene sulfonate (PSS) fragments. A two-dimensional phase transition to a denser surface phase at surface pressures of 25–30 mN/m and the formation of aggregates with a size of 40 nm in the Z-direction were found for applied polyelectrolyte layers without styrene monomers on an aqueous substrate.

Ion Transport and Solution Behavior of Polyanion-Type Li Salts in Nonaqueous Solvents

To achieve fast charging and discharging of Li-ion batteries, it is important to improve the ionic conductivity (σ) of the electrolyte as well as the Li-ion transference number (t Li) [1]. While nonaqueous polyelectrolyte solutions exhibit high Li-ion transference number(t Li = 0.81) upon immobilization of the anion on a polymer backbone, the ionic conductivity (σ = 1.3 mS cm-1) is inferior to that of conventional electrolytes (σ ~10 mS cm-1). One of the reasons for the low ionic conductivity is low dissociation degree caused by the counter-ion condensation on the polymer backbone. To gain an insight into a design strategy of polyelectrolyte-based liquid electrolytes for LIBs, we studied the effects of polyelectrolyte structure and solvent polarity on the transport properties and Li-ion solvation of the polyelectrolytes in carbonate solvents. Here, we employed two polyelectrolyte copolymers with different sequences; random copolymers of the Li salt of a weakly coordinating polyanion, poly[(4-styrenesulfonyl)-(trifluoromethanesulfonyl)amide] (poly(LiSTFSA)) with neutral comonomer unit, and poly[(4-maleimide-N-[(trifluoromethyl)sulfonyl]-benzenesulfonamide lithium salt] (poly(sa-PMI))-based alternating copolymers with neutral comonomer unit. For the random copolymers, the ionic conductivity increased as the ratio of the neutral comonomer increased. This was attributed to the suppression of counter-ion condensation and increased dissociation. The alternating copolymer solution showed higher dissociation than the random copolymers. The highest ionic conductivity was unexpectedly observed for the lowest polar mixture (such as a dimethyl carbonate rich mixture) at the highest salt concentration despite the low dissociation degree of the polyelectrolytes. A unique conduction resulting from the faster diffusion of transiently solvated Li ions along the interconnected aggregates of polyanion chains was suggested in the highly concentrated polyelectrolyte solutions in low polar solvents. A Li/LiFePO4 cell using the polyelectrolyte solution demonstrated a good charge-discharge performance and rate capability[2].

Complex Coacervates: From Polyelectrolyte Solutions to Multifunctional Hydrogels for Bioinspired Crystallization

Hydrogels represent multifarious functional materials due to their diverse ranges of applicability and physicochemical properties. The complex coacervation of polyacrylate and calcium ions or polyamines with phosphates has been uncovered to be a fascinating approach to synthesizing of multifunctional physically crosslinked hydrogels. To obtain this wide range of properties, the synthesis pathway is of great importance. For this purpose, we investigated the entire mechanism of calcium/polyacrylate, as well as phosphate/polyamine coacervation, starting from early dynamic ion complexation by the polymers, through the determination of the phase boundary and droplet formation, up to the growth and formation of thermodynamically stable macroscopic coacervate hydrogels. By varying the synthesis procedure, injectable hydrogels, as well as plastic coacervates, are presented, which cover a viscosity range of three orders of magnitude. Furthermore, the high calcium content of the calcium/polyacrylate coacervate (~19 wt.%) enables the usage of those coacervates as an ions reservoir for the formation of amorphous and crystalline calcium-containing salts like calcium carbonates and calcium phosphates. The exceptional properties of the coacervates obtained here, such as thermodynamic stability, viscosity/plasticity, resistance to acids, and adhesive strength, combined with the straightforward synthesis and the character of an ions reservoir, open a promising field of bioinspired composite materials for osteology and dentistry.

Constructing a Thin Layer of the Concentrated Polyelectrolyte Solution on the Hydrogel Surface That Can Considerably Improve the Solar Evaporation Efficiency

Constructing a Thin Layer of the Concentrated Polyelectrolyte Solution on the Hydrogel Surface That Can Considerably Improve the Solar Evaporation Efficiency

Competitive effects of anion mobility and viscous forces on the interactions of hyaluronic acid and alginic acid with hofmeister salts

The specific ion effect takes into account the hydration, mobility, and kosmotropic/chaotropic effects. However, another important aspect to consider is the solution viscosity, which influences ion mobility. A limited number of publications have considered the impact of specific ion effects on polyelectrolytes. However, none of the studies have considered the viscous effect of polyelectrolytes. This study aims to investigate the impact of kosmotropic and chaotropic anions on negatively charged alginic acid and hyaluronic acid using dynamic light scattering, rheology, and molecular dynamic simulations. Different concentration regimes and the change in the chain conformations in these regimes, along with the viscosity scaling and impact of the salts on the polyelectrolytes, have been discussed. An interesting finding regarding the solution viscosity was reported. The solution viscosity leads to the reversal of the diffusivity and viscosity trend of the polymer with kosmotropes and chaotropes. A threshold is also identified above which viscous forces dominate. Specific ion effects dominate below the threshold. It was concluded that the specific ion effect shows a competitive nature with the viscous forces in the case of a high-viscosity polyelectrolyte solution, which becomes an important aspect to consider for unveiling such interactions. Prior knowledge of the conformations of polymers can be used for designing drug delivery/nutrient delivery systems and for understanding phase separation behavior. Considering the viscosity of polymer solution becomes an important factor which, in turn, impacts the anion's mobility and ultimately influences the polymer conformations.

Harvesting Enhanced Blue Energy in Charged Nanochannels Using Semidiluted Polyelectrolyte Solution.

Blue energy generation in nanochannels based on salinity gradients is currently the most promising method in the area of nonconventional energy production. We used a semidiluted pure sodium carboxymethylcellulose (NaCMC)-KCl aqueous solution to study the characteristics of blue energy generation within a charged nanochannel. We solve the corresponding equations for ionic transport using a numerical technique based on the finite element method. Our analysis focused on the electric double layer (EDL) potential field, open circuit current, diffuse potential, electric conductance, maximum generated pore power, and maximum energy conversion efficiency by varying concentrations of the salt in the left-side reservoir and the bulk polyelectrolyte. The results indicate that as the polyelectrolyte concentration increases, the extent of EDL overlap considerably reduces. With an increase in polyelectrolyte concentration, the open circuit current increases, while the diffuse potential reduces. It was observed that both electrical conductance and maximal pore power improve considerably with higher polyelectrolyte concentrations. Interestingly, our modeling framework demonstrates a power density substantially higher (up to 16.31 W/m2) than earlier configurations and surpasses the established commercial limit (5 W/m2). Furthermore, our findings reveal that the reservoir salt concentration significantly affects the rate of decline in the maximum energy conversion efficiency as the polyelectrolyte concentration increases. The research paves the way for the development of high-power-density devices with several practical applications.

Diffusive Trends in Concentrated Oppositely-Charged Polyelectrolyte Solutions and Onset of Glassy Dynamics.

We utilize single particle tracking studies to investigate the diffusion of polylysine through concentrated matrices of cationic polylysine and anionic polyglutamic acid with no added salts. These studies show that diffusivity has a strong apparently exponential dependence on concentration in crowded systems that does not appear to be a function of the charge sign. These trends are consistent in both single-phase systems prepared at concentrated conditions and polymer-rich coacervate phases formed from dilute phase-separating systems. The likely origin of this behavior is the onset of glassy dynamics spurred by a decrease in plasticization by water and the large excluded volume associated with charge-bearing species. This effect can be contextualized through free volume-based theories such as the Vrentas-Duda model. Overall, we obtain dynamic behavior that is distinctly different from behavior observed in more dilute systems and warrants further investigation.

Oscillatory Interactions between Colloidal Particles in Polyelectrolyte Solutions: Linear Response Theory

Oscillatory Interactions between Colloidal Particles in Polyelectrolyte Solutions: Linear Response Theory

Two Methods Based on Integral Equation Approaches in Analyzing Polyelectrolyte Solutions: Macrophase Separation.

To understand the phase behaviors of polyelectrolyte solutions, we provide two analytical methods to formulate a molecular equation of state for a system of fully charged polyanions (PAs) and polycations (PCs) in a monomeric neutral component, based on integral equation theories. The mixture is treated in a primitive and restricted manner. The first method utilizes Blum's approach to charged hard spheres, incorporating the chain connectivity contribution by charged spheres via Stell's cavity function method. The second method employs Wertheim's multi-density Ornstein-Zernike treatment of charged hard spheres with Baxter's adhesive potential. The pressures derived from these methods are compared to available molecular dynamics simulations data for a solution of PAs and monomeric counterions as a limiting case. Two-phase equilibrium for the system is calculated using both methods to evaluate the relative strength of phase segregation that leads to complex coacervation. Additionally, the scaling exponents for a selected solution near its critical point are examined.

Critical adsorption and charge reversal in polyelectrolyte solutions: Analytical mean-field theory.

An analytical linearized mean-field theory is presented to describe the adsorption behavior of polyelectrolytes near charged colloidal surfaces with additional short-ranged non-electrostatic interactions. The coupling between the polyelectrolyte segment density and electrostatic potential is explicitly accounted for in a self-consistent manner. This coupling gives rise to highly non-linear behavior, such as oscillations of the electrostatic potential. We derive analytical expressions for the critical surface charge density σc, after which adsorption takes place, and recover the well-known σc∼ns3/2 scaling regime, where ns is the salt concentration. In addition, the theory yields a new ns1 scaling regime if the surface is hard and a unified ns1 scaling regime if the surface also possesses some short-ranged attraction with the polyelectrolyte. Furthermore, we derive an analytical expression to describe the critical polyelectrolyte concentration φc to achieve complete charge reversal, which is found to scale as φc ∼ σ2/(f2c2), where c is related to the magnitude of short-ranged interactions and f is the average charge per monomer of the polyelectrolyte. It is observed that within our theory, complete charge reversal can only take place if the short-ranged interactions are sufficiently strong to completely compensate for the entropy loss of adsorption.

GCMe: Efficient Implementation of the Gaussian Core Model with Smeared Electrostatic Interactions for Molecular Dynamics Simulations of Soft Matter Systems.

In recent years, molecular dynamics (MD) simulations have emerged as an essential tool for understanding the structure, dynamics, and phase behavior of charged soft matter systems. To explore phenomena across greater length and time scales in MD simulations, molecules are often coarse-grained for better computational performance. However, commonly used force fields represent particles as hard-core interaction centers with point charges, which often overemphasizes the packing effect and short-range electrostatics, especially in systems with bulky deformable organic molecules and systems with strong coarse-graining. This underscores the need for an efficient soft-core model to physically capture the effective interactions between coarse-grained particles. To this end, we implement a soft-core model uniting the Gaussian core model with smeared electrostatic interactions that is phenomenologically equivalent to recent theoretical models. We first parametrize it generically using water as the model solvent. Then, we benchmark its performance in the OpenMM toolkit for different boundary conditions to highlight a computational speedup of up to 34 × compared to commonly used force fields and existing implementations. Finally, we demonstrate its utility by investigating how boundary polarizability affects the adsorption behavior of a polyelectrolyte solution on perfectly conducting and nonmetal boundaries.

Why Single-Chain Nanoparticles from Weak Polyelectrolytes Can Be Synthesized at Large Scale in Concentrated Solution?

Here, the unresolved question of why single-chain nanoparticles (SCNPs) prepared from a weak polyelectrolyte (PE) precursor can be synthesized on a large scale in a concentrated solution is addressed, unlike SCNPs obtained from an equivalent neutral (nonamphiphilic) polymer precursor. The combination of the standard elastic single-chain nanoparticles (ESN) model -developed for neutral chains- with the classical scaling theory of PE solutions provides the key. Essentially, the long-range repulsion between electrostatic blobs in a weak PE precursor restricts the cross-linking process during SCNPs formation to the interior of each blob. Consequently, the maximum concentration at which PE-SCNPs can be prepared without interchain cross-linking is not determined by the full size of the PE precursor but, instead, by the smaller size of its electrostatic blobs. Therefore, PE-SCNPs can be synthesized up to a critical concentration where electrostatic blobs from different chains touch each other. This concentration can be 30 times higher than that for non-PE polymer precursors. Upon progressive dilution, the size of PE-SCNPs synthesized in concentrated solution increases until it reaches the bigger size of PE-SCNPs prepared under highly diluted conditions. PE-SCNPs do not adopt a globular conformation either in concentrated or in diluted solution. It shows that the main model predictions agree with experimental results.

Extreme dependence of dynamics on concentration in highly crowded polyelectrolyte solutions.

Charge-carrying species, such as polyelectrolytes, are vital to natural and synthetic processes that rely on their dynamic behavior. Through single-particle tracking techniques, the diffusivity of individual polyelectrolyte chains and overall system viscosity are determined for concentrated polylysine solutions. These studies show scaling dependences of D ~ c-6.1 and η ~ c7.2, much stronger than theoretical predictions, drawing the applicability of power law fits into question. Similar trends are observed in concentrated solutions prepared at various pH and counterion conditions. These hindered system dynamics appear universal to polyelectrolyte systems and are attributed to the large effective excluded volumes of polyelectrolyte chains inducing glassy dynamics. The framework of the Vrentas-Duda free-volume theory is used to compare polyelectrolyte and neutral systems. Supported by this theory, excluding counterion mass from total polymer mass results in all environmental conditions collapsing onto a common trendline. These results are applicable to crowded biological systems, such as intracellular environments where protein mobility is strongly inhibited.

Bubbling up in a Lab-on-a-Chip: A gravity-driven approach to the formation of polyelectrolyte multilayer capsules and foams

The generation of multi-functional capsules often requires the sequential deposition of different components on the surface of bubbles or drops. Batch-based methods lack fine control over the capsule sizes, including risk of fusion, and cannot ensure identical environments for each capsule. To overcome these issues, different micro/milli-fluidic methods have been developed in the past. However, a major challenge remains in combining an explicit and flexible control over the capsule generation and their residence time in the different solutions within the same device. Using for the first time the example of bubbles covered by layers of oppositely charged polyelectrolytes (PSS/PAH), we introduce an original millifluidic Lab-on-a-Chip device with two novel functions: (1) Size and separation of the bubbles are tuned at constant flow conditions via gas injection through a movible, circular dispense tip into the cross-flow of a rectangular channel. We provide a detailed exploration of the bubbling parameters together with physical justification of the observations. (2) The device exploits gravity to make the generated bubbles rise between horizontally stacked millifluidic chips containing each the controlled flow of a specific polyelectrolyte solution. In analogy with electric circuits, we show how the flow resistance of each chip can be adapted such that bubbles move smoothly between them while avoiding undesired mixing of the solutions. We show first examples of obtained multilayer capsules and discuss their peculiar features, in particular, their outstanding stability with respect to coalescence and dissolution. While our methods use polyelectrolyte assembly on bubbles, they can be readily transferred to other types of solutions or even to drops and particles.

Microstructures and Rheological Properties of Short-Side-Chain Perfluorosulfonic Acid in Water/2-Propanol.

The viscosity and viscoelasticity of polyelectrolyte solutions with a single electrostatic interaction have been carefully studied experimentally and theoretically. Despite some theoretical models describe experimental results well, the influence of multiple interactions (electrostatic and hydrophobic) on rheological scaling is not yet fully resolved. Herein, we systematically study the microstructures and rheological properties of short-side-chain perfluorosulfonic acid (S-PFSA), the most promising candidate of a proton exchange membrane composed of a hydrophobic backbone with hydrophilic side-chains, in water/2-propanol. Small-angle X-ray scattering confirms that semiflexible S-PFSA colloidal particles with a length of ~38 nm and a diameter of 1-1.3 nm are formed, and the concentration dependence of the correlation length (ξ) obeys the power law ξ~c-0.5 consistent with the prediction of Dobrynin et al. By combining macrorheology with diffusing wave spectroscopy microrheology, the semidilute unentangled, semidilute entangled, and concentrated regimes corresponding to the scaling relationships ηsp~c0.5, ηsp~c1.5, and ηsp~c4.1 are determined. The linear viscoelasticity indicates that the entanglement concentration (ce) obtained from the dependence of ηsp on the polymer concentration is underestimated owing to hydrophobic interaction. The true entanglement concentration (cte) is obtained by extrapolating the plateau modulus (Ge) to the terminal modulus (Gt). Furthermore, Ge and the plateau width, τr/τe (τr and τe denote reptation time and Rouse time), scale as Ge~c2.4 and τr/τe~c4.2, suggesting that S-PFSA dispersions behave like neutral polymer solutions in the concentrated regime. This work provides mechanistic insight into the rheological behavior of an S-PFSA dispersion, enabling quantitative control over the flow properties in the process of solution coating.