Polyelectrolyte Solutions Research Articles

Salt effects on knot dynamics in polyelectrolyte solutions

ABSTRACT We study the dynamics of linear polyelectrolyte (PE) knot in solution with doping salt by molecular dynamics simulations. The molecular mechanisms of PE knot dynamics are explained. The knot dynamics are the coupling results by the moving effect of chain entanglement and by the breathing effect of knot fluctuations. The moving effect is important as the whole chain is in the random coil state and becomes weak as shrinking to the close-to-globule (CTG) state. Interestingly, as the chain in the CTG state, the knot swells with occupying more segments. The breathing effect dominates the knot dynamics in the CTG state. This nontrivial behaviour (in comparison to neutral polymer knot) is prominent for the cases of doping salt with high concentration or of doping high-valent salt, which attributes to the enhanced electrostatic interactions and long-range fluctuation effects.

Nanodispersions of Polyelectrolytes Based on Humic Substances: Isolation, Physico-Chemical Characterization and Evaluation of Biological Activity.

Natural polyelectrolytes, including in the form of complexes with colloidal particles, are increasingly used in pharmacy due to the possibility of regulated attachment of medicinal substances and their targeted delivery to the target organ. However, the formation, stability, and molecular-mass characteristics of polyelectrolyte nanodispersions (ND) vary depending on the nature and composition of the medium of their origin. This is due to the lack of standardized approaches to quality control and regulatory documentation for most natural ND. In this paper, we first introduced the isolation, followed by investigations into their physico-chemical properties and bioactivity. Using the dried droplet method, we were able to detect the “coffee ring effect”. Fractographic studies of the surface structure of EHA and FA dried samples using SEM showed its heterogeneity and the presence of submicron particles encapsulated in the internal molecular cavities of polyelectrolyte. FTIR spectroscopy revealed the ND chemical structure of benzo-α-pyron and benzo-γ-pyron, consisting of nanoparticles and a branched frame part. The main elements detected by X-ray fluorescence in humic substance extract and fulvic acid include Si, P, S, K, Ca, Mn, Fe, Cu, Zn, whereas Fe is in high concentrations. The UV-spectra and fluorescent radiation demonstrated the possibility of studying the effect of the fulvate chromone structure on its optical properties. It is shown that dilution of the initial solutions of polyelectrolytes 1:10 contributes to the detection of smaller nanoparticles and an increase in the absolute value of the negative ζ-potential as a factor of ND stability. A study of the EHS effect on the SARS-CoV-2 virus infectious titer in the Vero E6 cell showed the effective against virus both in the virucidal scheme (the SI is 11.90–22.43) and treatment/prevention scheme (the SI is 34.85–57.33). We assume that polyelectrolyte ND prevent the binding of the coronavirus spike glycoprotein to the receptor. Taking into account the results obtained, we expect that the developed approach can become unified for the standardization of the ND natural polyelectrolytes complex, which has great prospects for use in pharmacy and medicine as a drug with antiviral activity.

Solution Properties of Polyelectrolytes with Divalent Counterions

Divalent ions are known to strongly influence the phase behavior, conformation, and flow properties of polyelectrolytes in solution. Here, we report small-angle neutron scattering and viscosity data for the magnesium salt of polystyrene sulfonate (MgPSS) in salt-free water and compare these results with analogous measurements for NaPSS. In a dilute solution, both salts are found to exhibit a rod-like conformation for high degrees of polymerization, but the chain dimensions of MgPSS are significantly smaller than for NaPSS, which is consistent with the lower charge density of MgPSS found from conductivity data. In the semidilute regime, the correlation length scales as ξ ≃ 3.7c–1/2 nm for NaPSS and ξ ≃ 5.4c–1/2 nm for MgPSS. At high concentrations, deviations to weaker power laws are observed for both salts. The variation of the viscosity with the degree of polymerization (ηsp ∼ N) is consistent with unentangled, Rouse-like dynamics. Fuoss-law-type behavior (ηsp ∼ c1/2) is observed at low polymer concentrations, which turns into a stretched exponential dependence at high c, perhaps due to an increase in the local friction experienced by polymer segments.

Overlap Concentration in Salt-Free Polyelectrolyte Solutions

For strongly charged polyelectrolytes in salt-free solutions, we use molecular dynamics simulations of a coarse-grained bead-spring model to calculate overlap concentrations c* and chain structure ...

Design of High-Relaxivity Polyelectrolyte Nanocapsules Based on Citrate Complexes of Gadolinium(III) of Unusual Composition.

Through nuclear magnetic relaxation and pH-metry, the details of the complexation of gadolinium(III) ions with citric acid (H4L) in water and aqueous solutions of cationic polyelectrolytes are established. It is shown that the presence of poly(ethylene imine) (PEI) in solution affects magnetic relaxation behavior of gadolinium(III) complexes with citric acid (Cit) to a greater extent than polydiallyldimethylammonium chloride (PDDC). A large increase in relaxivity (up to 50 mM−1s−1) in the broad pH range (4–8) is revealed for the gadolinium(III)–citric acid–PEI system, which is particularly strong in the case of PEI with the molecular weight of 25 and 60 kDa. In weakly acidic medium (pH 3–7), the presence of PEI results in the formation of two tris-ligand associates [Gd(H2L)3]3− and [Gd(H2L)2(HL)]4−, which do not exist in aqueous medium. In weakly alkaline medium (pH 7–10), formation of ternary complexes Gd(III)–Cit–PEI with the Gd(III)–to–Cit ratio of 1:2 is evidenced. Using transmission electron microscopy (TEM) and dynamic light scattering techniques (DLS), the formation of the particles with the size of 50–100 nm possessing narrow molecular-mass distribution (PDI 0.08) is determined in the solution containing associate of PEI with tris-ligand complex [Gd(H2L)2(HL)]4−.

Quantifying the Effect of Multivalent Ions in Polyelectrolyte Solutions

Quantifying the Effect of Multivalent Ions in Polyelectrolyte Solutions

Noncontact characterization of microstructured optical fibers coating in real time.

Functional nanocoatings have allowed hollow-core microstructured optical fibers (HC-MOFs) to be introduced into biosensing and photochemistry applications. However, common film characterization tools cannot evaluate the coating performance in situ. Here we report the all-optical noncontact characterization of the HC-MOF coating in real time. Self-assembled multilayers consisting of inversely charged polyelectrolytes (PEs) are deposited on the HC-MOF core capillary, and a linear spectral shift in the position of the fiber transmission minima with increasing the film thickness is observed as small as ∼1.5-6nm per single PE bilayer. We exemplify the practical performance of our approach by registering an increase in the coating thickness from 6±1 to 11±1nm per PE bilayer with increasing ionic strength in the PE solutions from 0.15 to 0.5 M NaCl. Additionally, we show real-time monitoring of pH-induced coating dissolving. Simplicity and high sensitivity make our approach a promising tool allowing noncontact analysis of the HC-MOF coating which is still challenging for other methods.

Simulation Study of the Conformational Properties of Diblock Polyelectrolytes in Salt Solutions.

Coarse-grained molecular dynamics simulations are performed to understand the behavior of diblock polyelectrolytes in solutions of divalent salt by studying the conformations of chains over a wide range of salt concentrations. The polymer molecules are modeled as bead spring chains with different charged fractions and the counterions and salt ions are incorporated explicitly. Upon addition of a divalent salt, the salt cations replace the monovalent counterions, and the condensation of divalent salt cations onto the polyelectrolyte increases, and the chains favor to collapse. The condensation of ions changes with the salt concentration and depends on the charged fraction. Also, the degree of collapse at a given salt concentration changes with the increasing valency of the counterion due to the bridging effect. As a quantitative measure of the distribution of counterions around the polyelectrolyte chain, we study the radial distribution function between monomers on different polyelectrolytes and the counterions inside the counterion worm surrounding a polymer chain at different concentrations of the divalent salt. Our simulation results show a strong dependence of salt concentration on the conformational properties of diblock copolymers and indicate that it can tune the self-assembly behaviors of such charged polyelectrolyte block copolymers.

Ion-Specific Effects on the Growth of Single Ice Crystals.

Understanding the effects of soluble impurities or suspended particles on ice growth is of significant importance from Earth science to materials engineering. Ions are common impurities with ice in a wide range of fields, but their effects on ice growth remain largely elusive. Here, we studied the ion-specific effects on single ice crystal growth in various electrolyte and polyelectrolyte solutions and found F- and NH4+ show remarkable abilities of inducing single ice crystals to form hexagonal shapes and reducing the growth rates of ice crystals. Molecular dynamics simulations reveal the accumulation of F- around the ice/solution interface that plays a key role in the shapes and growth rates of single ice crystals. The understanding of ion-specific effects on ice growth opens up more possibilities for improving related fields, e.g., freeze desalination and cryopreservation.

Polyelectrolyte solutions in Taylor-Couette flows

Taylor-Couette (TC) flow is ideal for studying the flow behavior of complex solutions due to the wide variety of available hydrodynamic flow states. For non-Newtonian solutions, the presence of polymers in solution changes the solution rheology, which in turn modifies accessible flow states. While significant prior work exists on the effects of elasticity and shear thinning of polymer solutions on TC flow, the effects of changes in polymer chain conformation on these properties and the resultant changes in the TC flow states have not been extensively studied. Here, we have explored the effects of changing polymer chain conformation of polyelectrolyte solutions on laminar and turbulent TC flow by using a quasi-static ramp protocol to vary the inner cylinder rotation rates. The ionic strength of the cationic polyacrylamide (CPAM) solution was varied to modify the equilibrium polymer equilibrium conformation and solution rheological properties. In general, as the increasing solution ionic strength increases polymer chain flexibility and decreases elasticity and degree of shear thinning, there is a shift toward more Newtonian-like flow behavior. Additionally, the effects of co- and counter-rotation of the cylinders on the stability of flow states were observed as a function of solution ionic strength, and phase diagrams of the resulting flow states were mapped as a function of the inner and outer cylinder Reynolds numbers. It was found that co-rotation of the cylinders stabilizes some of the polymer-influenced flow states, while counter-rotation de-stabilizes flow states.

Polyelectrolytes as Building Blocks for Next-Generation Membranes with Advanced Functionalities.

The global society is in a transition, where dealing with climate change and water scarcity are important challenges. More efficient separations of chemical species are essential to reduce energy consumption and to provide more reliable access to clean water. Here, membranes with advanced functionalities that go beyond standard separation properties can play a key role. This includes relevant functionalities, such as stimuli-responsiveness, fouling control, stability, specific selectivity, sustainability, and antimicrobial activity. Polyelectrolytes and their complexes are an especially promising system to provide advanced membrane functionalities. Here, we have reviewed recent work where advanced membrane properties stem directly from the material properties provided by polyelectrolytes. This work highlights the versatility of polyelectrolyte-based membrane modifications, where polyelectrolytes are not only applied as single layers, including brushes, but also as more complex polyelectrolyte multilayers on both porous membrane supports and dense membranes. Moreover, free-standing membranes can also be produced completely from aqueous polyelectrolyte solutions allowing much more sustainable approaches to membrane fabrication. The Review demonstrates the promise that polyelectrolytes and their complexes hold for next-generation membranes with advanced properties, while it also provides a clear outlook on the future of this promising field.

Comparative experimental and computational study of synthetic and natural bottlebrush polyelectrolyte solutions.

We systematically investigate model synthetic and natural bottlebrush polyelectrolyte solutions through an array of experimental techniques (osmometry and neutron and dynamic light scattering) along with molecular dynamics simulations to characterize and contrast their structures over a wide range of spatial and time scales. In particular, we perform measurements on solutions of aggrecan and the synthetic bottlebrush polymer, poly(sodium acrylate), and simulations of solutions of highly coarse-grained charged bottlebrush molecules having different degrees of side-branch density and inclusion of an explicit solvent and ion hydration effects. While both systems exhibit a general tendency toward supramolecular organization in solution, bottlebrush poly(sodium acrylate) solutions exhibit a distinctive "polyelectrolyte peak" in their structure factor, but no such peak is observed in aggrecan solutions. This qualitative difference in scattering properties, and thus polyelectrolyte solution organization, is attributed to a concerted effect of the bottlebrush polymer topology and the solvation of the polymer backbone and counterions. The coupling of the polyelectrolyte topological structure with the counterion distribution about the charged polymer molecules along with direct polymer segmental hydration makes their solution organization and properties "tunable," a phenomenon that has significant ramifications for biological function and disease as well as for numerous materials applications.

Preparation of shaped non-polyelectrolyte hydrogel particles with decomposable and recyclable performance by vortex ring freezing

The vortex-ring derived particles are new type of non-spherical hydrogel particles, which are prepared by imitating the process of vortex-ring in nature. However, the traditional existing vorticity ring derived hydrogel particles were prepared by dropping polyelectrolyte solution into contra-ion coagulation bath, which limited the choice of materials. In this paper, a strategy of preparation non-spherical hydrogel particles by using non-polyelectrolyte polyvinyl alcohol through the method of vortex ring was proposed. Based on the principle that the boraciated polyvinyl alcohol solution could be quickly gelled under alkaline condition, the spherical and various derivative shapes (red cell, bowl, dish, ring) of polyvinyl alcohol vortex-ring derived hydrogel particles (PVHP) were prepared. The hydrogel particles have the ability to assemble into different modules by dynamic borate bond in the hydrogel particles. Also, this dynamic borate bond endowed the PVHP decomposable and recyclable performances. In addition, two-compartments, three-compartments and magnetic PVHP were also prepared, endowing PVHP with several functions. which opens up a new environmentally friendly way for the preparation of multifunctional particles.

Multiphase Coacervates Driven by Electrostatic Correlations.

The liquid-liquid phase separation of a polyelectrolyte solution containing one type of negatively and two types of positively charged polymers with different charge densities is studied theoretically by random phase approximation (RPA). It is predicted that multicoacervate phases could coexist, driven purely by electrostatic correlations. The asymmetry of the linear charge density could induce an effective immiscibility between two positively charged polyelectrolytes, leading to the multiphase separation. Adding salt will induce the disappearance of the dilute phase, forming two coexisting complex phases, instead of fusion between coacervates. Raising temperature could either induce a two coexisting complex phase, or a dilute phase coexisting with a coacervate phase, depending on the bulk concentration. Our predictions are in good agreement with experiments and provide insights in the further designing of the multiphase coacervation system.

Charged Polymers: From Polyelectrolyte Solutions to Polyelectrolyte Complexes

Coarse-grained molecular dynamics simulations, random phase approximation (RPA) approach, and scaling analysis are used to study static and dynamic properties of concentrated polyelectrolyte solutions of positively charged chains with the degree of polymerization N+ = 400 and their mixtures with negatively charged chains with degrees of polymerization N– varying between 10 and 400. Simulations show that both the effective chain Kuhn length and mean-square end-to-end distance of a chain decrease with increasing monomer concentration, pointing out screening of the electrostatic interactions by surrounding chains. The structure factor S(q) has a characteristic peak at intermediate wavenumbers q* which location moves toward smaller q values with decreasing monomer concentration. It is demonstrated that the plateau in S(q) at a small q is controlled by system compressibility and increases with increasing degree of polymerization of negatively charged chains. These results are in agreement with S(q) calculated in the framework of the RPA approach considering a solution of neutral chains as a reference system. In the framework of this approach, the location of the maximum in the scattering function at q* scales with monomer concentration as ρ–0.25. Analysis of the chain dynamics in the mixtures of oppositely charged chains shows that chain relaxation is a combination of constraint release and chain reptation processes. Constraint release is demonstrated to be the dominant mechanism in mixtures with negatively charged chains having intermediate degrees of polymerization. The degree of polymerization Ne between entanglements of the tube and super tube for charged systems is found to scale with concentration as Ne ∼ ρ–2 with corresponding packing numbers Pe = 18.45 ± 0.93. This is in contrast with mixtures of neutral chains, where in addition to Ne ∼ ρ–2 scaling, the degree of polymerization between entanglements of the super tube follows scaling Ne ∼ ρ–4/3 with packing number Pe = 6.64 ± 0.19.

Preparation and characterization of silver orthophosphate photocatalytic coating on glass substrate

The photocatalytic activity of silver orthophosphate Ag3PO4 has been studied and shown to have a high photo-oxidation capability. However, there is few reported example of a simple method to prepare Ag3PO4 coatings on various substrates. In this study a novel and simple method to immobilize Ag3PO4 on the surface of glass substrates has been developed. A silver phosphate paste based on a polyelectrolyte solution was applied to a smooth glass surface. The resulting dried material was calcined to obtain a coating that remained on the glass substrate. The coating layer was characterized by X-ray diffraction and energy dispersive X-ray spectrometry, and the optical band gap of the material was determined. The results indicated that an Ag3PO4 coating responsive to visible light was successfully prepared. The coating, under visible light irradiation, has the ability to decompose methylene blue. Although the coating contained some elemental silver, this did not adversely affect the optical band gap or the photocatalytic ability.

Raman spectroelectrochemical study of pyrrole electropolymerization in the presence of sulfonated polyelectrolytes

We first performed in situ Raman spectroelectrochemical study of pyrrole electropolymerization in the presence of sulfonated polyelectrolytes. To obtain hydrophilic polypyrrole (PPy) films a galvanostatic polymerization of pyrrole was carried out on Pt-electrodes in aqueous solutions of flexible-chain and rigid-chain polyelectrolytes either in the acid or the salt forms. Common electrosyntheses in aqueous sulfuric acid and sodium sulfate were studied for comparison. It was found that polyelectrolytes were included into the film during the electropolymerization giving more protonated films. The form of polyelectrolyte (acid or salt) influences significantly the chemical structure of the forming PPy-polyelectrolyte complexes, the use of the acid forms of flexible-chain polyelectrolytes leading, in general, to higher content of bipolaronic fragments. Contrarily, the film prepared in the presence of rigid-chain polyacid is characterized by lower content of bipolaronic species, which may be explained by insufficient charge compensation in PPy by polyelectrolyte due to steric hindrances therein preventing mutual orientation of charged nitrogen cites and sulfonic groups of the rigid-chain polyacid.

Possibilities of Hyperinflammation Correction in COVID-19

Objective. To evaluate the effect of sodium meglumine succinate on the severity of the systemic inflammatory response syndrome when used in complex therapy in patients with severe COVID-19.Material and Methods. The clinical and laboratory data of 12 patients with the diagnosis «Novel coronavirus infection COVID-19 complicated by community-acquired bilateral polysegmental interstitial pneumonia» were analyzed. All patients underwent intensive therapy with a limited volume of water load in the intensive care unit in accordance with the recommendations of the Ministry of Health of the Russian Federation. Seven patients (observation group) received a polyelectrolyte solution containing meglumine sodium succinate (Reamberin) as part of the therapy at a daily dose of 5 ml/kg during the entire period of stay in the ICU (3–10 days). The control group included 5 patients who received a similar volume of a conventional polyelectrolyte solution containing no metabolically active substrates. The study was pilot in nature due to the small number of patients. The laboratory parameters of arterial and venous blood were measured at the following stages: 1) upon admission to the ICU; 2) 2–4 hours after the completion of Reamberin infusion; 3) 8–12 hours after drug administration; 4) 24 hours after the start of intensive care. Mortality rate and the incidence of thrombotic complications in the groups were assessed on the 28th day of observation. The presence of the therapeutic intervention effect was established using multivariate analysis of variance (MANOVA).Results. A positive effect of the study drug on the severity of systemic inflammatory response syndrome (SIRS) against the background of ongoing etiotropic therapy was noted. Efficiency criteria were the correction of hyperfibrinogenemia, normalization of the platelet count, decrease in the level of C-reactive protein, ferritin, and leukocytosis. A significant decrease in the frequency of thromboembolic events was observed within 28 days of treatment, as well as a reduction in the length of time the patients spent in the ICU.Conclusion. Based on the results of the pilot study, it can be assumed that the antihypoxic and antiradical effects of the drug contribute to the reduction of pulmonary and systemic endotheliitis, which is characteristic of severe forms of the disease and, as a result, inhibits the development of the systemic inflammatory response syndrome. The data obtained can serve as a basis for further in-depth studies.

Thickness Enhancement of Layer‐by‐Layer Multilayered Films Using Counter Polyelectrolyte‐Induced Colloidal Particles

The efficient formation of layer‐by‐layer (LbL) multilayered films is important for wide range applications and industrial productions especially when fabricating multilayered films with expensive materials. It was serendipitously discovered that the thickness of LbL film increased when omitting rinsing steps between the deposition steps. Based on this discovery, we developed an efficient method for systematically increasing the thickness of LbL films by adding a small amount of counter polyelectrolytes as additives in the polyelectrolytes solutions. It was found that the increased thickness is caused by colloidal particles induced by the aggregation of the polyelectrolytes.

Rheological Scaling of Ionic Liquid-Based Polyelectrolytes in the Semidilute Unentangled Regime from Low to High Salt Concentrations

Polymerized ionic liquids (PILs) are a special class of ion-containing polymers with ionic liquid structures. The viscoelastic properties of PILs in IL solutions are expected to be influenced by both polymer–polymer interaction and charge screening by IL ions, which becomes complex at high IL concentrations due to strong ionic correlations. In this work, we aim to understand the effect of the ionic correlations on the shear rheology of PIL in IL solutions in the semidilute unentangled (SU) polymer regime, with moderate polymer–polymer interactions. We conducted systematic rheological characterization of a PIL, poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide), in a mixture of an IL, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and a non-ionic solvent, dimethylformamide, to evaluate the specific viscosity ηsp and the longest relaxation time λ with varying IL concentrations cIL, at a fixed polymer concentration. We found that both ηsp and λ initially decreased with the increasing cIL, following the scaling theory of polyelectrolyte solutions in the low salt concentration regime. However, these values exhibited an upturn at high cIL. We explained the observed non-monotonic viscoelastic behavior by proposing a charge screening model for SU solutions, accounting for both modified screening length in concentrated IL solutions and complete charge screening. Our results demonstrate how the strong ionic correlation in concentrated IL solutions modifies the electrostatics of PILs and their corresponding viscoelastic properties in the presence of moderate polymer–polymer interactions.