Strong Polyelectrolyte Research Articles

PH-responsive SERS substrates based on AgNP-polyMETAC composites on patterned self-assembled monolayers

Patterned silver nanoparticle (NP)-poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (AgNP-polyMETAC) composites were prepared by electrochemical lithography, surface-initiated atom-transfer radical polymerization (SI-ATRP) and NP growth inside the polymer brushes. For this purpose, polymer brushes of poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (polyMETAC) were utilized as strong electrolyte brush system. These were introduced in form of patterned polymer brushes to create pH-responsive surface enhanced Raman scattering SERS substrates. It is well-known that the charges of strong polyelectrolyte chains are usually insensitive to pH changes, hence, rarely strong polyelectrolyte brushes have been utilized so far to study pH-responsive properties of such films. Here pH-insensitive polyMETAC brushes exhibit pH-sensitive properties and can be used as pH-responsive surfaces for SERS applications due to the embedding of AgNPs into the polymer brushes. When increasing the pH, the assembly of the AgNPs transfers from quasi two-dimensional (2D) aggregates, attaching mainly to the polymer surface, into a three-dimensional (3D) assembly, where the particles are penetrating into the brushes. These changes result in significant alterations of the SERS efficiency of the polymer brush composite. At pH 5, the enhancement of the Raman scattering approaches its maximum. The fabricated SERS substrates show a high sensitivity as well as good experimental reliability at different pH values. Moreover, electrochemical lithography was utilized to fabricate patterned SERS substrate, which allows an easy combination of multiple other functionalities in hierarchical structuring steps. In addition, the microstructure is in our studies beneficial because of a simplified and reliable characterization of the polymer brushes at defined sample areas. The introduction of the microstructured brush system is regarded moreover attractive for the development of high-throughput platforms for rapid, automated screening and analysis applications.

Influence of charge density and ionic strength on diallyldimethylammonium chloride (DADMAC)-based polyelectrolyte multilayer membrane formation

Although the layer-by-layer technique to produce nanofiltration membranes has been studied frequently, the influence of ionic strength of the coating solution in relation to the charge density lacks understanding. Here, we investigate the effect of both parameters systematically by comparing two strong polyelectrolyte sets: poly(acrylamide-co-diallyldimethylammoniumchloride) (P(AM-co-DADMAC))/ poly(sodium-4-styrenesulfonate) (PSS) and polydiallyldimethylammoniumchloride (PDADMAC)/PSS, with a polycation charge density of 32 and 100%, respectively. The influence of the charge density and the ionic strength during layer formation (5∙10−5 M – 1 M) has been researched in terms of polyelectrolyte adsorbance, membrane surface charge, and filtration performance. A low charge density is a limiting parameter for polyelectrolyte adsorption and retention, due to limited uptake of two bilayers. Consequently, it is impossible to form NF membranes with solely P(AM-co-DADMAC)/PSS layers. For high charge density polyelectrolytes, increasing the ionic strength is crucial to increase PE adsorption and MgSO4 retention. However, there is an opposite effect of ionic strength and charge density on membrane surface charge and pure water permeability. An increasing ionic strength results in a decreasing surface charge and increasing permeability for P(AM-co-DADMAC)-based membranes, and vice versa for PDADMAC. These opposite trends undoubtedly show the importance of simultaneously taking into account the charge density and ionic strength.

On the long-term pH stability of polyelectrolyte multilayer nanofiltration membranes

Long-term pH stability is critical for nanofiltration membranes in many applications, e.g. dairy and mining industry. We present a systematic study on the long-term pH stability of four different polyelectrolyte multilayer (PEM) nanofiltration membranes. The stability was assessed by comparing their performance before and after exposure to up to 1 M HNO3 (~pH 0) and 1 M NaOH (~pH 14), in terms of pure water permeance (PWP), salt retention, and molecular weight cut-off (MWCO).Poly(diallyldimethylammonium chloride) (PDADMAC)/poly(styrenesulfonate) (PSS) nanofiltration membranes show excellent stability under extreme acidic and basic conditions for more than 2 months (10.7 L m−2h−1bar−1 PWP, 95.5% MgSO4 retention, 279 g mol−1 MWCO), attributed to the use of strong polyelectrolytes, of which the charge is unaffected by pH. Poly(allylamine hydrochloride) (PAH)/PSS membranes show stable performance when exposed to extreme acidic conditions (9.7 L m−2h−1bar−1 PWP, 97.5% MgSO4 retention, 249 g mol−1 MWCO). Under these conditions, PAH remains charged and therefore a stable multilayer is maintained. PDADMAC/poly(acrylic acid) (PAA) and PAH/PAA membranes are not stable at extreme pH conditions.These results highlight that PEM nanofiltration membranes, especially PDADMAC/PSS membranes, have tremendous potential for use at extreme pH conditions. Compared to most commercially available membranes they have superior long-term stability and very relevant performance.

Effect of Protein Surface Charge Distribution on Protein–Polyelectrolyte Complexation

Charge anisotropy or the presence of charge patches at protein surfaces has long been thought to shift the coacervation curves of proteins and has been used to explain the ability of some proteins to coacervate on the "wrong side" of their isoelectric point. This work makes use of a panel of engineered superfolder green fluorescent protein mutants with varying surface charge distributions but equivalent net charge and a suite of strong and weak polyelectrolytes to explore this concept. A patchiness parameter, which assessed the charge correlation between points on the surface of the protein, was used to quantify the patchiness of the designed mutants. Complexation between the polyelectrolytes and proteins showed that the mutant with the largest patchiness parameter was the most likely to form complexes, while the smallest was the least likely to do so. The patchiness parameter was found to correlate well with the phase behavior of the protein-polymer mixtures, where both macrophase separation and the formation of soluble aggregates were promoted by increasing the patchiness depending on the polyelectrolyte with which the protein was mixed. Increasing total charge and increasing strength of the polyelectrolyte promote interactions for oppositely charged polyelectrolytes, while charge regulation is also key to interactions for similarly charged polyelectrolytes, which must interact selectively with oppositely charged patches.

Adsorption Behavior of Polyelectrolyte onto Alumina and Application in Ciprofloxacin Removal.

This study aims to investigate the adsorption behavior of a strong polyelectrolyte poly(styrenesulfonate) (PSS) onto alumina particles. Adsorption of PSS onto positively charged alumina surface increased with increasing ionic strength, indicating that non-electrostatic and electrostatic interaction controlled the adsorption. The removal of an emerging antibiotic ciprofloxacin (CFX) from water environment using PSS-modified alumina (PMA) was also studied. The removal of CFX using PMA was much higher than that using alumina particles without PSS modification in all pH ranges of 2–11. The removal of CFX reached 98% under the optimum conditions of pH 6, contact time of 120 min, adsorbent dosage of five milligrams per milliliter and ionic strength 104-M NaCl. The adsorption isotherms of CFX at different salt concentrations fit well with a two-step adsorption model, while the adsorption kinetic fit well with a pseudo-second-order model with a good correlation coefficient (R2 > 0.9969). The CFX-removal from a hospital wastewater using PMA was more than 75%. Our study demonstrates that adsorption of PSS onto alumina to modify the particle surface is important to form a novel adsorbent PMA for CFX-removal from water environments.

Polyelectrolyte Complex Membranes via Salinity Change Induced Aqueous Phase Separation.

Polymeric membranes are used on very large scales for drinking water production and kidney dialysis, but they are nearly always prepared by using large quantities of unsustainable and toxic aprotic solvents. In this study, a water-based, sustainable, and simple way of making polymeric membranes is presented without the need for harmful solvents or extreme pH conditions. Membranes were prepared from water-insoluble polyelectrolyte complexes (PECs) via aqueous phase separation (APS). Strong polyelectrolytes (PEs), poly(sodium 4-styrenesulfonate) (PSS), and poly(diallyldimethylammonium chloride) (PDADMAC) were mixed in the presence of excess of salt, thereby preventing complexation. Immersing a thin film of this mixture into a low-salinity bath induces complexation and consequently the precipitation of a solid PEC-based membrane. This approach leads to asymmetric nanofiltration membranes, with thin dense top layers and porous, macrovoid-free support layers. While the PSS molecular weight and the total polymer concentrations of the casting mixture did not significantly affect the membrane structure, they did affect the film formation process, the resulting mechanical stability of the films, and the membrane separation properties. The salt concentration of the coagulation bath has a large effect on membrane structure and allows for control over the thickness of the separation layer. The nanofiltration membranes prepared by APS have a low molecular weight cutoff (<300 Da), a high MgSO4 retention (∼80%), and good stability even at high pressures (10 bar). PE complexation induced APS is a simple and sustainable way to prepare membranes where membrane structure and performance can be tuned with molecular weight, polymer concentration, and ionic strength.

Colorimetric sensing of barium ion in water based on polyelectrolyte-induced chemical etching of silver nanoprisms

Because water contamination by barium ion (Ba2+) is still common, the ability to detect Ba2+ in aqueous media is important. However, the development of an easy-to-use and point-of-care sensing method for detecting Ba2+ in aqueous media has proven challenging. In the present study, a colorimetric sensing platform for detecting Ba2+ in an aqueous medium was developed. The platform stands on the basis of the localized surface plasmon resonance (LSPR) properties of Ag nanoprisms, where a strong polyelectrolyte, poly(styrene-4-sulfonate) (PSS), is used as a powerful chemical etchant for the nanoprisms. Upon the addition of PSS to a solution of the Ag nanoprisms, the sharp tips of the Ag nanoprisms were immediately etched and the nanoprisms spontaneously transformed into spheroidal nanostructures, giving rise to dramatic changes in their LSPR properties. The chemical etching reaction of Ag nanoprisms exposed to PSS was retarded in the presence of Ba2+, which enabled the design of a new chemical sensing platform for the sensitive and selective detection of Ba2+ in aqueous media. The proposed Ba2+ sensing platform using highly anisotropic Ag nanostructures and a polyelectrolyte etchant offers numerous advantages over existing platforms, including naked-eye recognition and safe use and handling; hence, the developed platform can be used at the point of care.

Electroresponsive Polyelectrolyte Brushes Studied by Self-Consistent Field Theory.

End-grafting of polyelectrolyte chains to conducting substrates offers an opportunity to fabricate electro-responsive surfaces capable of changing their physical/chemical properties (adhesion, wettability) in response to applied electrical voltage. We use a self-consistent field numerical approach to compare the equilibrium properties of tethered strong and weak (pH-sensitive) polyelectrolytes to applied electrical field in both salt-free and salt-containing solutions. We demonstrate that both strong and weak polyelectrolyte brushes exhibit segregation of polyions in two populations if the surface is oppositely charged with respect to the brush. This segregation gives rise to complex patterns in the dependence of the brush thickness on salt concentration. We demonstrate that adjustable ionization of weak polyelectrolytes weakens their conformational response in terms of the dependence of brush thickness on the amplitude of the applied voltage.

Polyelectrolyte Based Sensors as Key to Achieve Quantitative Electronic Tongues: Detection of Triclosan on Aqueous Environmental Matrices.

Triclosan (TCS) is a bacteriostatic used in household items that promotes antimicrobial resistance and endocrine disruption effects both to humans and biota, raising health concerns. In this sense, new devices for its continuous monitoring in complex matrices are needed. In this work, sensors, based on polyelectrolyte layer-by-layer (LbL) films prepared onto gold interdigitated electrodes (IDE), were studied. An electronic tongue array, composed of (polyethyleneimine (PEI)/polysodium 4-styrenesulfonate (PSS))5 and (poly(allylamine hydrochloride/graphene oxide)5 LbL films together with gold IDE without coating were used to detect TCS concentrations (10−15–10−5 M). Electrical impedance spectroscopy was used as means of transduction and the obtained data was analyzed by principal component analysis (PCA). The electronic tongue was tested in deionized water, mineral water and wastewater matrices showing its ability to (1) distinguish between TCS doped and non-doped solutions and (2) sort out the TCS range of concentrations. Regarding film stability, strong polyelectrolytes, as (PEI/PSS)n, presented more firmness and no significant desorption when immersed in wastewater. Finally, the PCA data of gold IDE and (PEI/PSS)5 sensors, for the mineral water and wastewater matrices, respectively, showed the ability to distinguish both matrices. A sensitivity value of 0.19 ± 0.02 per decade to TCS concentration and a resolution of 0.13 pM were found through the PCA second principal component.

Multilayer capsules made of weak polyelectrolytes: a review on the preparation, functionalization and applications in drug delivery.

Multilayer capsules have been of great interest for scientists and medical communities in multidisciplinary fields of research, such as drug delivery, sensing, biomedicine, theranostics and gene therapy. The most essential attributes of a drug delivery system are considered to be multi-functionality and stimuli responsiveness against a range of external and internal stimuli. Apart from the highly explored strong polyelectrolytes, weak polyelectrolytes offer great versatility with a highly controllable architecture, unique stimuli responsiveness and easy tuning of the properties for intracellular delivery of cargo. This review describes the progress in the preparation, functionalization and applications of capsules made of weak polyelectrolytes or their combination with biopolymers. The selection of a sacrificial template for capsule formation, the driving forces involved, the encapsulation of a variety of cargo and release based on different internal and external stimuli have also been addressed. We describe recent perspectives and obstacles of weak polyelectrolyte/biopolymer systems in applications such as therapeutics, biosensing, bioimaging, bioreactors, vaccination, tissue engineering and gene delivery. This review gives an emerging outlook on the advantages and unique responsiveness of weak polyelectrolyte based systems that can enable their widespread use in potential applications.

Modulation of the internal structure and surface properties of natural and synthetic polymer matrices by graphene oxide doping

Controlling the surface properties and structure of thin nanosized coatings is of primary importance in diverse engineering and medical applications. Here we report on how the nanostructure, growth mechanism, thickness, roughness, and hydrophilicity of nanocomposites composed of weak natural or strong synthetic polyelectrolytes (PE) can be tailored by graphene oxide (GO) doping. GO reverses the build‐up mechanism affecting the internal structure and the hydrophilicity in a way depending on the type of the PE‐matrix. The extent of GO‐adsorption and its impact on the surface morphology was found to be independent on the type of the underlying PE‐matrix. The nanostructure of the hybrid films is not significantly altered when a single surface‐exposed GO‐layer is deposited, while increasing the number of embedded GO‐layers leads to pronounced surface heterogeneity. These results are expected to have valuable impact on the construction strategies of coatings with tunable surface properties.

Ionic hydrogen bond effects on polyelectrolyte brushes beyond the hydronium and hydroxide ions.

Herein, we have demonstrated that the properties of both strong and weak polyelectrolyte brushes including hydration, stiffness, conformation, and wettability can be tuned by the hydrogen bonding between the bound counterions and the grafted chains beyond the hydronium and hydroxide ions. This will greatly extend the application of ionic hydrogen bond effects in polymer systems.

Ionic liquid-induced nanoporous structures of polymer films.

We present a new strategy for the fabrication of nanoporous polymer films assembled using strong polyelectrolyte pairs in ionic liquid aqueous solutions. These nanoporous films show good anti-reflection properties.

Rheological investigations of water-soluble polysaccharides from the Tunisian brown seaweed Cystoseira compressa

Rheological characteristics of a sodium alginate and a fucoidan extracted from the brown seaweed Cystoseira compressa harvested from Kerkennah island (Sfax, Tunisia) were investigated. Steady-shear flow and dynamical viscoelasticity were evaluated to describe physicochemical properties of the GulA-rich alginate (ManA/GulA, M/G = 0.77) and highly-ramified fucoidan in semi-diluted media depending on polymer concentration, shear rate, temperature, added mono- (KCl and NaCl) and divalent (CaCl2) salts. Alginate solutions exhibited shear-thinning behavior, with a temperature-dependent behavior highly correlated to the power-law model and the Arrhenius relationship. The results showed strong thixotropic and polyelectrolyte properties, influenced by addition of monovalent and divalent cations. The dynamic rheological characteristics showed a fluid-like viscoelastic behavior (tan δ > 1) whereas the critical overlap concentration C* and specific polymer constant ks were respectively 11 g.L−1 and 4.4 using Williamson model. Fucoidan solutions displayed a shear-thinning behavior with a low viscoelasticity character influenced by temperature and monovalent salts. The flow and viscoelastic characteristics of polysaccharides were described by the Ostwald model.

Counterion-Tunable Thermosensitivity of Strong Polyelectrolyte Brushes.

In this work, poly(sodium styrene sulfonate) brushes have been employed as a precursor to prepare thermosensitive strong polyelectrolyte brushes (SPBs) through a counterion exchange strategy. The substitution of hydrophilic Na+ counterions by hydrophobic tetraalkylphosphonium counterions leads to a thermoresponsivity of the SPBs. The thermosensitive properties including hydration, stiffness, and surface water wettability of the SPBs can be modulated by the type of the tetraalkylphosphonium counterions. Nevertheless, the wet thickness of the SPBs with tetraalkylphosphonium counterions does not exhibit an obvious temperature dependency due to the high steric barrier in the crowded environment of SPBs generated by the large tetraalkylphosphonium counterions. The mixtures of small Na+ counterions and large tetraalkylphosphonium counterions are employed to realize the thermosensitive wet thickness without sacrificing other thermoresponsive properties of the SPBs because the mixed counterions can bring both a certain hydrophobicity and some free space to the brushes. This work opens up the opportunities available for the use of counterions to tune the thermosensitivity of SPBs.

Swelling and dye adsorption properties of polyelectrolyte semi-IPNs including of acrylamide/(3-acrylamidopropyl)trimethyl ammonium chloride/poly(ethylene glycol)

ABSTRACT This study explains the preparation, characterization, and application of acrylamide-based cross-linked polymers as a synthetic sorbent materials for anionic dye calconcarboxylic acid (CCA). Different series of strong polyelectrolyte poly[acrylamide/(3-acrylamidopropyl)trimethyl ammonium chloride)], P(AAm/APTMAC) hydrogels and poly[(acrylamide/(3-acrylamidopropyl)trimethyl ammonium chloride)/poly(ethylene glycol)], P(AAm/APTMAC/PEG) semi-IPNs were prepared. FT-IR analysis and SEM technique were applied and swelling/diffusion parameters were calculated for characterization. Binding parameters of CCA were evaluated via linearization methods such as Klotz (R 2 = 0.9933), Scatchard (R 2 = 0.9902), and Langmuir (R 2 = 0.9952). Quantitative information on the swelling/adsorption behaviors of novel polyelectrolyte hydrogels and semi-IPNs which can be used in many potential applications were given in this study.

Surface Forces of Asymmetrically Grown Polyelectrolyte Multilayers: Searching for the Charges.

Surface forces are used to investigate the polymer conformation and the surface charge of polyelectrolyte multilayers. Films are prepared from strong polyelectrolytes with low and high linear charge density at 0.1 M NaCl, namely poly(diallyldimethylammonium) (PDADMA) and poly(styrenesulfonate) (PSS). The multilayer has two growth regimes: in the beginning, the film can contain as many positive as negative monomers. After about 15 deposited layer pairs, a linear growth regime characterized by an excess of cationic PDADMA monomers occurs. Independent of the film composition, at preparation conditions, the film surface is flat, uncharged and partially hydrophobic. Surface force measurements at decreased ionic strength provide insight. For PSS-terminated films electrostatic forces are found. At the beginning of multilayer formation, the surface charge density is negative. However, in the linear growth regime it is positive and low (one charge per 200-400 nm2). This reversal of surface charge density of PSS-terminated films is attributed to excess PDADMA-monomers within the film. PDADMA terminated films show steric forces, chains protrude into the solution and form a pseudobrush, which scales as a polyelectrolyte brush with a low grafting density (1900 nm2 per chain). We suggest a model of polyelectrolyte multilayer formation: PDADMA with its low linear charge density adsorbs with weakly bound chains. Monovalent anions within the film compensate PDADMA monomer charges. When PSS adsorbs onto a PDADMA-terminated multilayer, PSS monomers replace monovalent anions. While electrostatic bonds are formed and dissolved within the polyelectrolyte multilayer, the surface charge density remains zero.

Influence of pH on the formation of a polyelectrolyte complex by dissipative particle dynamics simulation: From an extended to a compact shape.

This work aims to investigate the influence of pH on the mechanism of assembly of macromolecules. We studied the effect of the pH on the interaction of two polyelectrolytes of opposed charge, having the same size, by means of dissipative particle dynamics method. The system consisted of a strong cationic and a weak anionic polyelectrolyte in an aqueous solution containing monovalent counterions. The analysis was made by varying the pH of the solution, which modifies the charge fraction of the weak anionic polyelectrolyte with a dissociation acid constant pKa of 5.5, while the polycation is fully charged in all the pH range used, characteristic of a strong polyelectrolyte. In order to describe the influence of pH on the complexation process, we have analyzed the pair radial distribution functions polyanion-counterion, polycation-counterion, and polyanion-polycation. The complex conformation was studied by means of the radius of gyration and the end-to-end distance of both chains as the pH varied from 1 to 14. A relevant finding obtained here was the relationship between the radial distribution functions and the counterion release from the polyelectrolytes, which leads to a reduction in the size of the complex when pH increased. Surprisingly, a transition from an extended to a compact polyelectrolyte complex was obtained when the pH reached the dissociation acid constant pKa of the weak polyelectrolyte. This systematic study can help to understand a large number of more realistic problems in biological systems such as protein complex, chromatin phase transition, or in complex systems applied in biomedical science.

Synthesis of (AB)n‐, AnBn‐, and AxBy‐type amphiphilic and double‐hydrophilic star copolymers by RAFT polymerization

ABSTRACTThe synthesis, characterization, and postpolymerization functionalization of star copolymers by RAFT polymerization, using ethylene glycol dimethacrylate as the difunctional monomer for core formation via crosslinking, is presented in this work. The “arm first” approach was used for the synthesis of PDMAEMAnPOEGMAn double‐hydrophilic mikto‐arm stars and PDMAEMAxPLMAy amphiphilic miktoarm stars, while the “core first” approach was used for the synthesis of (PDMAEMA‐b‐POEGMA)n double‐hydrophilic star block copolymers. Methyl iodide was used as the quaternizing agent for the transformation of the star copolymers into strong cationic star polyelectrolytes, through reaction on the dimethylamino groups of PDMAEMA blocks. The stars were characterized at the molecular level by SEC and proton nuclear magnetic resonance. Preliminary light scattering experiments, using THF and H2O as the solvents, were performed in order to get information regarding the solution behavior of the novel star copolymers synthesized. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1771–1783

Stable colloidal dispersion of octylated Ti3C2-MXenes in a nonpolar solvent

Two-dimensional (2D) early transition metal carbides and/or nitrides (MXenes) have shown significant potential in a wide variety of applications. The majority of MXene research has utilized aqueous colloidal dispersions of MXenes because of the unique hydrophilicity of the MXene surface. In some cases, however, aqueous dispersions have various disadvantages such as the degradation of MXenes in long-term storage, incompatibility with water-insoluble polymers, and dewetting on low-surface-energy substrates. Herein, we demonstrated a stable nonpolar colloidal dispersion of MXenes chemically grafted with lipophilic octyltriethoxysilanes (MX@OTS). A high grafting density of OTS on the MXene surface was achieved by employing a strong acid polyelectrolyte, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), as an OTS (water insoluble)-in-water emulsifier while the reaction was carried out in the aqueous media in which the hydrophilic MXenes showed the best dispersion. The remarkable hydrophobicity of these octylated MXenes was demonstrated by a high water-contact angle on the macroscopic MX@OTS surface as well as the high interfacial tension between the MX@OTS-in-hexane dispersion and water, which was almost identical to that for pure hexane/water. Despite the negligible surface charging, the hydrophobic MX@OTS showed excellent colloidal stability in very nonpolar hexanes over four weeks.