Polyelectrolytes Of High Charge Density Research Articles

The comparison of adsorption kinetics of polystyrene particles with two polyelectrolytes near the isoelectric points

Microplastics are widely regarded as an emerging pollution owing to ubiquitous environmental distributions and toxicological characteristics. The adsorption kinetics of microplastic particles with polyelectrolytes is vital to improve the removal efficiency of microplastics, however, the adsorption kinetics of polyelectrolytes onto the particle surface is far from well understood near the isoelectric point. The adsorption of high and low charge density polyelectrolytes was investigated near the isoelectric point based on the measurement of the electrophoretic mobility. The mobility of particles adsorbing high charge density polyelectrolytes reaches the plateau in several seconds, whereas low charge density polyelectrolyte takes about dozens of seconds to reach the plateau of zero. The adsorption of high charge density polyelectrolyte is enhanced with the decrease of ionic strength, whereas, low charge density polyelectrolyte demonstrates the opposite tendency against ionic strength. All results will facilitate the analysis of the flocculation process of microplastic particles.

Effect of mixing intensity on flocculation kinetics of polystyrene latex particles with high-charge density polyelectrolyte at various ionic strengths

Effect of mixing intensity on the flocculation kinetics of polystyrene latex (PSL) particles with a high-charge density polyelectrolyte was analyzed using a small stirred vessel equipped with a four-paddle impeller and four baffles. The intensity of mixing was estimated by the effective shear rate evaluated in terms of collision frequency between the colloidal particles. This estimation was performed by measuring the salt-induced rapid coagulation of PSL particles as a function of the rate of impeller rotation. Acrylamide-(dimethylamino)ethyl methacrylate methyl chloride with nominal molecular weight of 4.9×106 g mol−1 was used as a flocculant. An enhancement factor, determined by the ratio of the rate of flocculation with a polyelectrolyte in the initial stage to that of salt-induced rapid coagulation, was used as the evaluation index. It was found that the enhancement factor goes through a maximum with an increase in mixing intensity, thus implying the presence of an optimal mixing intensity for flocculation. Further, considerable fluctuation was observed for a low mixing intensity and the degree of fluctuation slightly increased as the ionic strength increased.

Brownian flocculation of negatively charged latex particles with low charge density polycation at various ionic strengths

Rate of Brownian flocculation of polystyrene latex particles with low charge density polyelectrolyte (σ=4%, Mw=5.2×106g/mol) was measured by Coulter Counter as a function of the ionic strength. As reported in the case of high charge density polyelectrolyte [L. Feng, Y. Adachi, A. Kobayashi, Colloid Surf. A. 440 (2014) 155–160], the rate of flocculation goes through a maximum against polyelectrolyte dosage, and a maximum rate of flocculation was observed near the isoelectric point. However, several important trends are different from the results obtained with high charge density polyelectrolyte. (1) The rate of flocculation is always slower than that of salt-induced rapid coagulation, even at the isoelectric point. (2) The optimum polyelectrolyte dosage corresponding to the isoelectric point appears several times higher. (3) The shift of isoelectric point was also observed with an increase of ionic strength but toward a lower polyelectrolyte dosage. (4) The thickness of adsorbed polyelectrolyte layer was found to be detectable (about 15nm) at the optimum dosage of flocculation where the fastest rate was observed. These results suggest a picture of bridging flocculation that competes with steric effects of adsorbed polyelectrolytes.

Multilayers of Low Charge Density Polyelectrolytes on Thin Films of Carboxymethylated and Cationic Cellulose

Multilayers with low charge density polyelectrolytes assembled on thin films of cellulose were studied by piezoelectric microgravimetry. The substrates were produced from colloidal suspensions of cotton fibers before and after modification with cationic and anionic groups via epoxy intermediates of quaternary ammonium and carboxymethylation, respectively. Two different levels of ionicity were used for each cellulosic substrate in order to investigate the role of the supporting surface in the buildup of the multilayer. It was found that while electrostatic interactions were leading factors in the assembly of high molecular weight, low charge density polyelectrolytes, other effects such as van der Waals and secondary cooperative forces played important roles. The charge properties of the substrate and the adsorbing polymer were relevant to the behavior of the self-assembled multilayers. Sequential additions of weak polyelectrolytes formed viscoelastic layers on all cellulose substrates. Adsorption of the first layer depended heavily on the charge characteristics of the substrate while the buildup of subsequent layers was mainly affected by the outermost adsorbed polymer. The polyelectrolyte multilayer formation with highest total adsorbed mass occurred on unmodified cellulose surfaces; therefore, in the case of the low charge density polyelectrolytes studied, substrate ionicity and functionalization may not be a requirement. Finally, the effect of anionic weak polyelectrolytes added after the first adsorbed polymer pair is highlighted in the context of reported observations for polyelectrolytes of high charge density.

Polyelectrolyte Adsorption on Thin Cellulose Films Studied with Reflectometry and Quartz Crystal Microgravimetry with Dissipation

Thin cellulose films were prepared by dissolving carboxymethylated cellulose fibers in N-methyl morpholine oxide and forming thin films on silicon wafers by spin-coating. The adsorption of cationic polyacrylamides and polydiallyldimethylammonium chloride onto these films was studied by stagnation point adsorption reflectometry (SPAR) and by quartz crystal microgravimetry with dissipation (QCM-D). The polyelectrolyte adsorption was studied by SPAR as a function of salt concentration, and it was found that the adsorption maximum was located at 1 mM NaCl for polyelectrolytes of low charge density and at 10 mM NaCl for polyelectrolytes of high charge density. Electrostatic screening led to complete elimination of the polyelectrolyte adsorption at salt concentrations of 300 mM NaCl. According to the QCM-D analysis, the cellulose films showed a pronounced swelling in water that took several hours to complete. Subsequent adsorption of polyelectrolytes onto the cellulose films led to a release of water from the cellulose, an effect that was substantial for polyelectrolytes of high charge density at low salt concentrations. The total mass change including water could therefore show either an increase or a decrease during adsorption onto the cellulose films, depending on the experimental conditions.

Interaction of polyelectrolyte with digested sewage sludge and lignite in sludge dewatering

Physical conditioners, often known as skeleton builders, are commonly used for enhancing the rate and the extent of water removal of polyelectrolyte-flocculated sewage sludge. In this study, the interactions of two different cationic polyelectrolytes with lignite (a low rank coal) in conditioning of digested sewage sludge are investigated. Vacuum filtration tests, zeta potential measurements and floc population measurements are performed on flocculated sludge and mixtures of the flocculated sludge and the lignite. The results for the flocculated sludge demonstrate the classical flocculation mechanisms of charge neutralization and particle–particle bridging. However, when lignite is mixed with the flocculated sludge in the conditioning process, the lignite particles agglomerate with the flocculated sludge by polymer bridging, which improves the dewatering properties of the flocculated sludge. The lignite particles strongly agglomerate with the flocculated sludge for the high molecular weight (MW) and low charge density (CD) polyelectrolyte, but the agglomeration is weaker and shear sensitive for the low MW and high CD polyelectrolyte.

Structural and Mechanical Properties of Polyelectrolyte Multilayer Films Studied by AFM

Mechanical properties of polyelectrolyte multilayer thin films were studied by nanoinden- tation experiments using an atomic force microscope. We obtained force-distance measurements for a model polycation/polyanion multilayer system, poly(allylamine hydrochloride) (PAH), and an azobenzene- containing polyelectrolyte (P-Azo) prepared at varying charge densities. The relative Young's modulus of the films was determined as a function of the ionization fraction of the multilayer films, prepared to have identical thickness. Multilayer films assembled with polyelectrolytes of high charge density exhibited an elastic modulus that was significantly larger (nearly 2 orders of magnitude) than those prepared with low charge density. An estimate of the relative loop length between cross-links in the multilayer films is then ascertained by analogy to previously studied covalently cross-linked polymer networks. The modulus values in our films ranged from 10-2 to 10-4 kPa, and this implies loop lengths of 1-50 segments. Atomic force microscopy force-distance measurements were also used to compare the relative adhesion values between polycation and polyanion layers in films constructed with varying charge densities. This was done by coating an AFM tip with multilayers and indenting into a surface containing the same multilayer film but capped with the oppositely charged surface polyelectrolyte layer. Adhesion values were typically between 0.5 and 6.7 nN and were found to depend on the ionic cross-link density of the PAH/P-Azo film, in which the highly ionically cross-linked samples exhibited the largest adhesion.

Nanoscale morphology of polyelectrolyte self-assembled films probed by scanning force and near-field scanning optical microscopy

We applied shear force microscopy, an analog to attractive-mode atomic force microscopy, and near-field scanning optical microscopy (NSOM) to the study of surface roughness and nanoscale morphology in polyelectrolyte self-assembled layers. Our data show that the surface roughness of multilayer films on glass grows linearly with the number of polyelectrolyte bilayers for the first 10 bilayers, and then asymptotes at a surface roughness of 4 nm. The surface of these films is characterized by bumps of 100–500 nm in diameter and 25–50 nm tall. In addition, the size and density of the bumps for each bilayer are uncorrelated to the previous surface. This result is in sharp contrast to what is observed for other self-assembled layer structures, such as metal-phosphonate and Langmuir–Blodgett self-assembly, where the surface roughness linearly increases with the number of layers. Subsurface morphology in thin films was observed via fluorescence NSOM of a dye-doped polyelectrolyte film. The NSOM images show domains of higher and lower fluorescence intensity, which could be assigned to local changes in the film thickness, suggesting that the dye molecules are uniformly distributed within the film. We also show that both the initial and asymptotic surface roughness can be dramatically decreased if the bare glass surface is treated with a high charge-density polyelectrolyte, such as poly(ethyleneimine) (PEI), prior to the bilayer formation. Finally, we observed that if the initial substrate is rough, growth of the polyelectrolyte layers acts to smooth the surface until the equilibrium value is reached.

Pervaporation separation of water/alcohol mixtures using composite membranes based on polyelectrolyte multilayer assemblies

Composite pervaporation membranes composed of an asymmetric polyamide-6 membrane and an ultrathin self-assembled polyelectrolyte separating layer are described. The supporting membrane was prepared from both an unmodified polyamide-6 and a comb-like polymer with carboxyl terminated polyamide-6 side chains. A high end group concentration was found to be advantageous for sufficient adhesion of the multilayer systems on the supports. Up to 20 layers were deposited onto the membrane surface by dipping the membranes in aqueous solutions containing oppositely charged polyelectrolytes. The polyanions used were poly(acrylic acid), poly(styrene sulfonic acid) and alginic acid. The polycations used were poly(diallyldimethylammoniumchloride), chitosan and poly(ethylenimine). Performance of these membranes depends strongly on the layer number and on the type of polyelectrolytes. In general, membranes modified with two weak polyelectrolytes of high charge density gave the best separation properties while those modified with strong polyelectrolytes of low charge density led to poorer separation properties. However, the highest separation factor (≥10,000) for a water/2-propanol mixture (12/88 w/w) at permeate flux of 300 g/m 2h was obtained with six double layers consisting of poly(ethylenimine) and alginic acid. These composite membranes were stable over an operating period of at least 400 h.

Polyelectrolytes of High Charge Density in Organic Solvents. Synthesis and Viscosimetric Behavior

An easy anion exchange between electrolyte monomers of the quaternary ammonium halide type such as [(2-methacryloyloxy)ethyl]trimethylammonium chloride or 1-vinyl-3-methylimidazolium iodide and various cyanocarbon salts such as 1,2,2-tricyanoethenolate, 1,1,2,3,3-pentacyanopropenide, α,α-dicyano-p-toluoylcyanide, or p-(tricyanovinyl)phenyldicyanomethide readily leads to a series of new hydrophobic electrolyte monomers with yields generally over 70%. [(2-Methacryloyloxy)ethyl]trimethylammonium 1,1,2,3,3-pentacyanopropenide is a most representative example. Its free radical polymerization in homogeneous solution (DMF, 60 °C) currently yields atactic chains (Bernoulli stereopropagation process, probability of meso placement Pm = 0.31) of fairly high degree of polymerization (DPw ∼ 1600) which show an unique spectrum of solubility in dipolar organic solvents (dipole moment μ > 2.6 D) covering a very broad range of dielectric constants (e ∼ 10−180). Viscosity measurements performed in 13 solvents allow us to a...

Polyelectrolyte solutions. Electrical conductivity and counterion condensation

AbstractWe have analyzed the electrical conductivity of a linear high charge density polyelectrolyte aqueous solution, finding that the counterion association order follows the same pattern as that described for a cyclic monomeric polyelectrolyte, i.e. NO > Br− > Cl− > F−. However, these counterions interact in a very different manner with this polyion, making Eisenberg's relationship inapplicable in this system. Consequently, an alternative method is proposed for treating data.

Simulations on the Primitive Electrolyte Environment of a High Charge-density Polyelectrolyte. A Sampling Problem and its Solution

Abstract We show that the classical Metropolis Monte Carlo (MMC) algorithm converges very slowly when applied to the primitive electrolyte environment for a high charge-density polyelectrolyte. This slowness of convergence, which is due to the large density inhomogeneity around the polyelectrolyte, produces noticeable errors in the ion distribution functions for MMC runs of 1.3 × 106 trial steps started from nonequilibrium distributions. We report that an algorithm which we call DSMC (for density-scaled Monte Carlo) overcomes this problem and provides relatively rapid convergence in this application. We suggest that DSMC should be well-suited for other Monte Carlo simulations on physical systems where large density inhomogeneities occur.

Conductivity of polyelectrolytes in very dilute solutions

The conductivity behaviour of polyelectrolytes in very dilute solutions has been investigated. It is in general not possible to extrapolate the equivalent conductivity, Λ, to infinite dilution, primarily because the solvent conductivity, κ0, is affected by the polyelectrolyte. However, from the slope of the conductivity against concentration curve it is possible to determine the limiting equivalent conductivity, Λ°, which characterises the conductivity in a concentration region where the interionic interactions are limited to interactions between the polyion and its counter-ion atmosphere.Conductivity measurements were carried out with polyacrylic acid and carboxymethylated hydroxyethyl cellulose. Of the latter polyelectrolyte, samples with widely differing charge densities were used. From measurements performed with the sodium and potassium salts of the polyacids the limiting equivalent conductivity and friction coefficient of the polyions were determined. The experimental results in general did not conform to current polyelectrolyte theories and there was no direct evidence of counter-ion condensation in polyelectrolytes of high charge density.