Aqueous Polyelectrolyte Solutions Research Articles

Hanging aqueous polyelectrolyte “Dropbags” at liquid surface for Bio-inspired systems

Water surfaces serve as habitats for numerous creatures and have inspired a wide range of innovations. Herein, we demonstrate the fabrication of bag-shaped hanging droplets (dropbags) at the liquid surface using miscible polyelectrolyte aqueous solutions. The surface tension at the liquid-liquid interface maintains the top-opening structure of the dropbag, and the coacervate layer, formed rapidly by electrostatic interactions, inhibits the diffusion of large molecules, providing the dropbag with a flexible shape. Particularly, the "scattered dropbags-in-dropbag" (SDID) system was employed to accelerate the hatching of brine shrimp, such diverse compartmentalized structures and biophilic materials have the potential to be used for the cultivation and research of various creatures.

Structural Properties of Ions and Polyelectrolytes in Aqueous Solutions under External Electric Fields: The Sign Effect

Structural Properties of Ions and Polyelectrolytes in Aqueous Solutions under External Electric Fields: The Sign Effect

Viscosity scaling and entangled solution rheology in aqueous and salt solutions of polyelectrolytes containing diallyl dimethylammonium groups

Viscosity scaling and entangled solution rheology in aqueous and salt solutions of polyelectrolytes containing diallyl dimethylammonium groups

Effect of isopropanol cosolvent on the rheology and spinnability of aqueous polyacrylic acid solutions

AbstractWe investigate the effect of alcohol fraction (isopropanol, IPA) in a binary water‐alcohol solvent mixture on the shear and extensional rheological properties, as well as the role of viscoelasticity on fiber formation of poly(acrylic acid) (PAA) in electrospinning. Comparison of the scaling of both specific viscosities ηsp and extensional relaxation times λE of PAA in water–IPA mixtures, showed stronger scaling compared to salt‐free aqueous polyelectrolyte solutions, except for the ηsp in the unentangled regime displaying a polyelectrolyte‐like scaling ηsp ~ c0.5 for all IPA%. Such deviation suggested IPA induces association/aggregation of PAA. However, the trends between ηsp and λE magnitudes as a function of IPA% differ for concentrations compared in the entangled regime. The ηsp as well as their elastic moduli exhibit a maximum, whereas λE increases monotonically with IPA%, suggesting a complex interplay of various interactions are dictating their structure in water‐IPA mixtures, affecting their shear and extensional response differently. Electrospinning experiments showed increasing IPA% reduces the onset of both beaded and uniform fibers. Analysis using dimensionless numbers indicated the enhancement of their elasticity by IPA, and the consequent stabilizing effect on their jets/filaments against break‐up during electrospinning, plays a role in the improvement of their fiber formation.

Polyelectrolyte-multivalent molecule complexes: physicochemical properties and applications.

The complexation of polyelectrolytes with other oppositely charged structures gives rise to a great variety of functional materials with potential applications in a wide spectrum of technological fields. Depending on the assembly conditions, polyelectrolyte complexes can acquire different macroscopic configurations such as dense precipitates, nanosized colloids and liquid coacervates. In the past 50 years, much progress has been achieved to understand the principles behind the phase separation induced by the interaction of two oppositely charged polyelectrolytes in aqueous solutions, especially for symmetric systems (systems in which both polyions have similar molecular weight and concentration). However, in recent years, the complexation of polyelectrolytes with alternative building blocks such as small charged molecules (multivalent inorganic species, oligopeptides, and oligoamines, among others) has gained attention in different areas. In this review, we discuss the physicochemical characteristics of the complexes formed by polyelectrolytes and multivalent small molecules, putting a special emphasis on their similarities with the well-known polycation-polyanion complexes. In addition, we analyze the potential of these complexes to act as versatile functional platforms in various technological fields, such as biomedicine and advanced materials engineering.

Small Amphiphile-Based Coacervation.

Coacervation plays an important role in the molecular assembly towards soft materials with a diversity of function (e. g., underwater adhesives of mussels and membraneless organelles). Coacervation is observed when one homogenous solution spontaneously separates into two immiscible liquid phases of low and high solute concentration, also known as liquid-liquid phase separation (LLPS), which enables spatiotemporally local concentration of specific molecules. LLPS is a common physical phenomenon in aqueous solutions of polyelectrolytes, surfactants and biomolecules, which has been extensively explored for applications in the fields of environmental remediation, cosmetic formulation, protein purification, extractive fermentation and pharmaceutical microencapsulation. This review summarizes the development of LLPS with low molecular weight amphiphiles to construct simple and complex coacervates using conventional surfactants and novel amphiphiles such as azobenzene-derivatives and peptides. We also highlight the applications of these amphiphile coacervates in the extraction of biomolecules, construction of protocell models and drug delivery.

Thermodynamic modeling of aqueous polyelectrolyte solutions with mixed-valent counterions

Thermodynamic modeling of aqueous polyelectrolyte solutions with salts is of significant interest for many industrial applications. This study applies the polyelectrolyte Nonrandom Two-liquid activity coefficient model to aqueous polyelectrolyte solutions with mixed-valent counterions. A modified Delocalized Binding Theory was proposed to determine the polyion condensation fractions of the mixed counterions. This modified theory accounts for the electrostatic binding of the counterions on the polyion, the dissociation entropy of the counterions, and the electrostatic interactions between the uncondensed ionic species. Given the polyion condensation fractions, the critical value of Manning’s parameter ξ and the amounts of uncondensed polyions and counterions can be calculated along with the activity coefficients of mobile ions. The model successfully correlates experimental data for various aqueous polyelectrolyte systems with mixed-valent counterions.

Structures of cationic and anionic polyelectrolytes in aqueous solutions: the sign effect.

In this study, we use molecular dynamics simulation to explore the structures of anionic and cationic polyelectrolytes in aqueous solutions. We first confirm the significantly stronger solvation effects of single anions compared to cations in water at the fixed ion radii, due to the reversal orientations of asymmetric dipolar H2O molecules around the ions. Based on this, we demonstrate that the solvation discrepancy of cations/anions and electrostatic correlations of ionic species can synergistically cause the nontrivial structural difference between single anionic and cationic polyelectrolytes. The cationic polyelectrolyte shows an extended structure whereas the anionic polyelectrolyte exhibits a collapsed structure, and their structural differences decline with increasing the counterion size. Furthermore, we corroborate that multiple cationic polyelectrolytes or multiple anionic polyelectrolytes can exhibit largely differential molecular architectures in aqueous solutions. In the solvation dominant regime, the polyelectrolyte solutions exhibit uniform structures; whereas, in the electrostatic correlation dominant regime, the polyelectrolyte solutions exhibit heterogeneous structures, in which the likely charged chains microscopically aggregate through counterion condensations. Increasing the intrinsic chain rigidity causes polyelectrolyte extension and hence moderately weakens the inter-chain clustering. Our work highlights the various, unique structures and molecular architectures of polyelectrolytes in solutions caused by the multi-body correlations between polyelectrolytes, counterions and asymmetric dipolar solvent molecules, which provides insights into the fundamental understanding of ion-containing polymers.

Electrostatically self-assembled filamentous sodium alginate/ε-polylysine fiber with antibacterial, bioadhesion and biocompatible in suturing wound

In the work, a novel filamentou sodium alginate (SA) /ε-polylysine (PL) fiber with excellent mechanical properties and controllable sizes is prepared in an efficient and environmentally friendly manner via continuous pulling of an electrostatically assembled SA/PL composites at the contact interface of aqueous solutions of cationic polyelectrolyte ε-PL and anionic natural polysaccharide SA. The SA/PL fiber exhibits good antibacterial activity, low cytotoxicity, anti-hemolysis, bioadhesion, and environmental friendliness due to its natural raw materials and green preparation process. In vivo experiments have shown that the SA/PL fiber can promote the healing and repair of skin wounds on the backs of mice via resistance to pathogen infection, reduction of inflammation, and anti-allogeneic allergy of the wound. In summary, these results demonstrate that the SA/PL fiber is a green and biosafe multifunctional natural polymer material, with potential applications in suturing wound.

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−.

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.

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.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications.

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing–thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Cytocompatible drug delivery devices based on poly[(2-dimethylamino) ethyl methacrylate]/chondroitin sulfate polyelectrolyte complexes prepared in ionic liquids

Important researches aim for the development of efficient and cheaper biomedical devices based on natural polysaccharides. In this facet, polyelectrolytes complexes (PECs) are interesting materials for biomedical purposes because they can be prepared without using conventional and volatile organic solvents and toxic crosslinkers, commonly used in the synthesis of chemical hydrogels. For the first time, we used ionic liquids (1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids, [Bmim][BF4], [Omim][BF4] and [Dmim][BF4]) to prepare poly[(2-dimethylamino) ethyl methacrylate]/chondroitin sulfate (PDMAEMA/CS) PECs in aqueous media. The ionic liquids promoted changes in the PECs morphology, influencing the size of the pore significantly. The presence of ionic liquids in aqueous polyelectrolyte solutions enhanced the interactions between poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA) and chondroitin sulfate (CS), providing organized structures when compared with the PEC yielded only in an aqueous solution. The materials obtained in the ionic liquids' presence were stable and no toxic against epithelial and fibroblast cells. We can modulate the PEC properties by tuning both ionic liquid type and content.

Colorimetric detection of Cu2+ using of a mixture of ponceau 6R and a cationic polyelectrolyte in aqueous solution

A colorimetric chemosensor is reported for Cu2+ by a simple mixture of two commercially available reagents, ponceau 6R (P6R) and poly(diallyldimethylammonium chloride) (PDADMAC) in an aqueous solution. P6R interacted electrostatically with PDADMAC to form the self-aggregate of P6R and exhibit a different sensing capability from P6R alone. The mixture showed high sensitivity and specific selectivity for detection of Cu2+ compared with various physiological and environmentally important metal ions. The addition of Cu2+ caused a hypsochromic shift with a distinct color change from red to yellow. While, upon adding Cu2+ to P6R alone, the solution underwent no distinct color change. The binding mode of P6R with Cu2+ was determined to be a 2:1 stoichiometry from Job plot and Cu2+ titration experiments. The results provide an easy method for developing new colorimetric sensors for metal ions by a combination of anionic dyes and cationic polyelectrolytes.

Multiswitchable photoacid-hydroxyflavylium-polyelectrolyte nano-assemblies.

Light- and pH-responsive nano-assemblies with switchable size and structure are formed by the association of a photoacid, anthocyanidin, and a linear polyelectrolyte in aqueous solution. Specifically, anionic disulfonated naphthol derivatives, neutral hydroxyflavylium, and cationic poly(allylamine) are used as building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to alter the ternary system through external triggering are accessible. The structure and trigger effects can be controlled through the component ratios of the samples. Dynamic and static light scattering (DLS, SLS) and ζ-potential measurements were applied to study the size and the stability of the particles, and information on the molecular structure was gained by UV–vis spectroscopy. Isothermal titration calorimetry (ITC) provided information on the thermodynamics and interaction forces in the supramolecular assembly formation.

Single-molecule studies reveal the distinction of strong and weak polyelectrolytes in aqueous solutions.

Polyelectrolytes are an important class of functional polymers that have the advantages of both polymers and electrolytes due to the presence of charges, and have prospective applications in many fields. The charge of the backbone is an important factor affecting the properties of polyelectrolytes. Therefore, the complex interactions caused by the charges in polyelectrolyte solutions pose a challenge to the study of polyelectrolyte systems, and there is no consensus on the distinction between the behavior of strong and weak polyelectrolytes in solution. Based on single-molecule force spectroscopy (SMFS), the distinction of strong and weak polyelectrolytes is clarified for the first time at the single molecular level by comparing the single-chain elasticity in different environments. It is expected that the single-molecule study will provide the theoretical and experimental basis for the further application of polyelectrolytes.

PH-Dependent complexation and polyelectrolyte chain conformation of polyzwitterion-polycation coacervates in salted water.

The phase behavior and chain conformational structure of biphasic polyzwitterion-polyelectrolyte coacervates in salted aqueous solution are investigated with a model weak cationic polyelectrolyte, poly(2-vinylpyridine) (P2VP), whose charge fraction can be effectively tuned by pH. It is observed that increasing the pH leads to the increase of the yielding volume fraction and the water content of dense coacervates formed between net neutral polybetaine and cationic P2VP in contrast to the decrease of critical salt concentration for the onset of coacervation, where the P2VP charge fraction is reduced correspondingly. Surprisingly, a single-molecule fluorescence spectroscopic study suggests that P2VP chains upon coacervation seem to adopt a swollen or an even more expanded conformational structure at higher pH. As the hydrophobicity of P2VP chains is accompanied by a reduced charge fraction by increasing the pH, a strong pH-dependent phase and conformational behaviors suggest the shift of entropic and enthalpic contribution to the underlying thermodynamic energy landscape and chain structural dynamics of polyelectrolyte coacervation involving weak polyelectrolytes in aqueous solution.

Colorimetric detection of Mn(ii) based on a mixture of an anionic pyridylazo dye and a cationic polyelectrolyte in aqueous solution

AbstractWe have developed a simple and valuable method for the construction of a colorimetric chemosensor for detecting Mn(ii) in aqueous media. The chemosensor was prepared by mixing two commercial products, an anionic organic dye, 2‐(5‐nitro‐2‐pyridylazo)‐5‐(N‐propyl‐N‐sulphopropylamino)phenol (Nitro‐PAPS) and a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC). Upon gradual addition of Mn(ii) to the chemosensor, the absorption spectra showed a remarkable bathochromic shift concomitantly with a distinct colour change from yellow to blue‐green, while Nitro‐PAPS alone could not detect Mn(ii) in a colorimetric method. PDADMAC played a key role in sensing Mn(ii) for the mixture. The colour change might be due to the formation of the aggregate obtained through electrostatic interactions of a Nitro‐PAPS‐based Mn(ii) complex with PDADMAC. This investigation can inform the development of a new chemosensor by the combination of an anionic dye and a cationic polyelectrolyte.

Molecular aggregates of pyronin dyes with polyelectrolyte polystyrene sulfonate (PSS) in aqueous solution

Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containing anionic polyelectrolyte polystyrene sulfonate (PSS) has been studied by using steady-state and time-resolved fluorescence and UV–vis absorption spectroscopy techniques. Although H-aggregates of these pyronin dyes have been previously observed in colloidal suspension, this is the first report of their J-aggregates obtained as a function of dye concentration by using constant concentration of PSS in solution. The best dye concentrations for the J-aggregates were determined as 2.4 × 10−5 M and 1.2 × 10-4 M for PyB and PyY, respectively. Moreover, aggregation equilibrium constants (KD) and thermodynamic functions were determined as a function of temperature for H-type aggregation. By employing the exciton theory, angle (α) between the molecular transition dipole moments and the long aggregate axis, and the intermolecular distance (R) were also calculated for each dye aggregates. In addition, the fluorescence lifetime values were determined from fluorescence decay measurements for the monomer and aggregated species of pyronin compounds in polyelectrolyte aqueous solution.