Surface Charge Density Of Particles Research Articles

Adsorption mechanism of poly(vinyl alcohol) on the surfaces of synthetic zeolites: sodalite, Na-P1 and Na-A

The structure of poly(vinyl alcohol)—PVA layers adsorbed on the synthetic zeolites surfaces was determined. Three zeolites: sodalite, Na-P1 and Na-A were obtained using hydrothermal conversion of fly ash with aqueous sodium hydroxide. The effects of solution pH and zeolite type on the adsorption mechanism of the polymer were examined. The analysis of the results obtained by means of spectrophotometric and microelectrophoretic measurements as well as potentiometric titrations enabled description of interfacial behaviour of adsorbed macromolecules. It was shown that the presence of poly(vinyl alcohol) layers modifies the surface properties of applied zeolites. The evidence of this are changes in the surface charge density and zeta potential of solid particles observed in the polymer presence. Moreover the PVA chains exhibit different adsorption affinity for the examined zeolites depending mainly on the mean pore size of these aluminosilicates which is very important for penetration of internal zeolite structure by polymeric macromolecules.

Investigations of chromium(III) oxide removal from the aqueous suspension using the mixed flocculant composed of anionic and cationic polyacrylamides.

The main purpose of experiments was determination of the adsorption mechanism of two forms of ionic polyacrylamide (PAM) on the surface of chromium(III) oxide dispersed in the aqueous medium. This was performed in relation to anionic polyacrylamide (AN PAM) and cationic one (CT PAM) in the simple systems (containing only one selected polymer) and in the mixed systems (containing both ionic forms of PAM). The turbidimetry was applied to determine the stability of examined suspensions. To explain the obtained changes in suspension stability after the polymer addition, polyacrylamide adsorbed amount, surface charge density and zeta potential of solid particles were determined. It was found that the solution pH, order of both adsorbates addition as well as the time interval between the AN and CT PAM addition have considerable influence on the structure of polymeric adsorption layer formed on the Cr2O3 surface. It was also proved that changes in the PAM adsorbed amount in the systems containing mixed adsorbates result from formation of AN PAM - CT PAM complexes. They are bounded at the interface in the formed multilayer. As a result, the dual-polymer flocculation occurs more effectively than the destabilization process in the suspensions containing only one type of adsorbate.

STABILITY OF METAL OXIDE SUSPENSION IN THE CATIONIC POLYACRYLAMIDE PRESENCE

The stability of metal oxide aqueous suspension in the cationic polyacrylamide (PAM) presence was examined. For this purpose the turbidimetry method was applied. Chromium(III) oxide, zirconium(IV) oxide and aluminium(III) oxide were selected for experiments. The ionic polyacrylamide with molecular weight 7 000 000 Da and containing 50% of cationic groups was applied as an adsorbate. To explain the obtained changes in the stability parameters of metal oxide suspensions in the polymer presence the spectrophotometric and electrokinetic measurements were performed. They enable determination of PAM adsorbed amount, as well as surface charge density and zeta potential of solid particles without and covered with polymeric layers. The analysis of these data led to the description of the most probable stability mechanism of solid suspension containing cationic polyacrylamide

Relaxation Effect on Intrapore Diffusivities of Highly Charged Colloidal Particles Confined in Porous Membranes

During the particle intrapore diffusion, the particle–pore hydrodynamic interaction enhances the drag on the particle, resulting in a particle diffusivity reduction. For charged particles submerged in an electrolytic solution, the distortion of electrical double layer caused by particle motion creates an additional drag: a phenomenon known as the relaxation effect. Such effect on intrapore diffusivities of rigid spherical particles confined in long cylindrical pores is determined by employing a perturbation scheme involving particle Peclet number. Comparison between present simulation results and previous results from perturbations involving both particle Peclet number and surface charge density indicates that the perturbation involving surface charge density overestimates the electrokinetic retardation. Our results demonstrate that, whereas a particle surface charge density increase always amplifies the excess drag due to relaxation, effects of pore surface charge density are more complicated and dependent on values of particle surface charge density and Debye length. If a highly charged particle is confined in a charged pore, this additional drag increases as a function of Debye length if the Debye length is small, but becomes constant despite the increasing Debye length if the Debye length is comparable or larger than the pore radius. For particles confined in uncharged pores, however, the Debye length increase always amplifies the electrokinetic retardation, causing the particle diffusivity reduction of a highly charged particle in an uncharged pore to be larger than that of a similar particle confined in a charged pore if the Debye length is comparable to or larger than the pore radius.

Flocculation efficiency of the Sinorhizobium meliloti 1021 exopolysaccharide relative to mineral oxide suspensions – A preliminary study for wastewater treatment

Abstract The main aim of the study was to examine the Sinorhizobium meliloti1021 exopolysaccharide (EPS) flocculation efficiency relative to mineral oxide suspensions and verify if EPS can be used in the wastewater treatment procedure. The paper compares the EPS adsorption influence on the stability of various mineral oxide suspensions (chromium(III) oxide, silica, zirconia). Moreover, it indicates the solid whose aqueous suspension is the most destabilized in the EPS presence. The selected adsorbents have different surface properties. They are characterized by different pHpzc (zero surface charge) and pHiep (isoelectric) points. The highest adsorption amount was observed on the chromium(III) oxide surface. It resulted in the greatest changes in the particle zeta potential and surface charge density. The exopolysaccharide addition affects the stability of all mineral oxide suspensions. The most significant changes were observed for chromium(III) oxide and zirconia at pH 9. Under these conditions there is a bridging flocculation in the system, so the S. meliloti exopolysaccharide can be regarded as a potential flocculant related to these solids. In turn, the silica suspension stability changes insignificantly in the EPS presence.

Synthesis, processing and electron paramagnetic resonance response of Y1.98Eu0.02O3 micro rods

Innovating dosimetric materials, which includes design and development of new dosimetric materials based on rare earth oxides, is challenging. Yttrium oxide (Y[Formula: see text]O[Formula: see text] is one of the most important sesquioxides and presents crystal characteristics that enable doping with rare earth ions, making it a promising material for radiation dosimetry. This paper reports on the development and measurement of Electron Paramagnetic Resonance (EPR) signal response for Y[Formula: see text]Eu[Formula: see text]O[Formula: see text][Formula: see text]micro rods that have undergone facile low-pressure hydrothermal synthesis and bio-prototyping. As- synthesized powders with narrow sub-micrometer particle size distribution with d[Formula: see text][Formula: see text] of 584 nm exhibited a reactive surface, which led to the formation of stable aqueous suspensions by controlling the surface charge density of particles through alkaline pH adjustment. Ceramic samples with dense microstructure were formed by sintering at 1600 [Formula: see text]C for 4h at ambient atmosphere. Y[Formula: see text]Eu[Formula: see text]O[Formula: see text][Formula: see text]micro rods were irradiated using a [Formula: see text]Co source with doses from 1 to 100 kGy, and EPR spectra were measured at room temperature in X-band microwave frequencies. Sintered samples exhibited linearity of the main EPR signal response from 10 Gy to 10 kGy. Supralinearity was observed for higher doses, which is possibly ascribed to formation of more defects. Using europium as a dopant enhanced the EPR signal of yttrium rods remarkably, due to 4f–4f transitions of the Eu[Formula: see text] ion. These innovative findings make europium-doped yttrium oxide a promising material for radiation dosimetry.

Formation of Colloidal Nanocellulose Glasses and Gels.

Nanocellulose (NC) suspensions can form rigid volume-spanning arrested states (VASs) at very low volume fractions. The transition from a free-flowing dispersion to a VAS can be the result of either an increase in particle concentration or a reduction in interparticle repulsion. In this work, the concentration-induced transition has been studied with a special focus on the influence of the particle aspect ratio and surface charge density, and an attempt is made to classify these VASs. The results show that for these types of systems two general states can be identified: glasses and gels. These NC suspensions had threshold concentrations inversely proportional to the particle aspect ratio. This dependence indicates that the main reason for the transition is a mobility constraint that, together with the reversibility of the transition, classifies the VASs as colloidal glasses. If the interparticle repulsion is reduced, then the glasses can transform into gels. Thus, depending on the preparation route, either soft and reversible glasses or stiff and irreversible gels can be formed.

The Investigation of Dynamic Changes of the Particle Surface Charge with Resistive-Pulse Technique

In the resistive-pulse technique, individual particles passing through a pore cause transient changes of the transmembrane current, and the amplitude of the current change corresponds to the object size. This method has been applied to detect cells, viruses, molecules (e.g. DNA and proteins) and particles. With the special structure of track-etched polycarbonate pores, i.e. narrower entrances and cylindrical interior, the events of highly carboxylated charged polystyrene particles can show a current decrease when a particle enters the pore, a flat region in the center part, and a current increase when the particle exits the pore. The current increase results from concentration polarization as well as ionic sourcing effects, which depend on the particle surface charge density. Thus, the characteristics of the obtained resistive-pulse signal carry information not only on the size of the objects, but also on dynamic changes of the particle surface charge via protonation/deprotonation of surface carboxyl groups. Experiments were performed with a pH gradient set across the pore, so that the particles while translocating would change their effective surface charge due to the dependence of protonation of carboxyl groups on the local proton concentration. Analysis of the current increase at the end of the event revealed that the process of deprotonation/protonation required longer time than the transit time. This finding was unexpected, because the transit times were tens of milliseconds thus significantly longer then the chemical reaction time estimated based on proton diffusion. Our experiments also indicated that a longer pore and a higher pH gradient led to a more complete protonation/deprotonation in the pore during transit. Using our finding, we designed a protocol to trap individual particles in a pore for as long as 3 seconds. The experiments are important for developing new methods which can be used to in situ characterize and precisely control single molecules and particles.

The effect of particle surface charge density on filter cake properties during dead-end filtration

During the filtration of suspended organic material, filter cakes with high specific resistances are often formed. The properties of these filter cakes differ markedly from the classical filtration properties derived from inorganic suspensions, not only by having a higher specific resistance but also by being highly compressible. These organic substances typically have a high surface charge density, due to the different functional groups on their surfaces, so a set of model particles was synthesized in which the surface charge density can be varied while keeping all other properties constant. The synthesized monodisperse particles all have a polystyrene core and varying ratios of charged (i.e. polyacrylic acid) and uncharged (i.e. hydroxypropyl cellulose) stabilizing polymers covalently grafted to the surface. All used particles have proven to be stable against aggregation during storage and are easily redispersed upon agitation. Aqueous suspensions of the particles were filtered in a dead-end setup at constant pressure to determine the filter cake properties. Results indicate that the specific cake resistance, cake compressibility, and cake porosity increase with the particle surface charge. Comparison with two empirical models of filter cake resistance demonstrates that particle charge is more important than is porosity, as highly charged filter cakes have resistances orders of magnitude higher than calculated, which is not the case for filter cakes of uncharged particles. DLVO theory suggests that the results cannot be explained in terms of classical double-layer effects, even in the extreme case of very small interparticle distances. Deviations from this classical behavior, arising from the confinement of charged particles by charged walls or pores, are a possible explanation, allowing the high resistances to be interpreted as increased osmotic pressure due to the distribution of counterions in the pores. Calculations indicate that osmotic pressure increases with particle charge and with decreasing porosity, but remains close to zero for uncharged particles.

Probing charges on solid-liquid interfaces with the resistive-pulse technique.

Our manuscript addresses the issue of probing an effective surface charge that any surface can acquire at the solid/liquid interface. Even if a particle is predicted to be neutral based on its chemical structure, the particle can carry finite surface charges when placed in a solution. We present tools to probe the presence of surface charge densities of meso-particles, characterized with zeta potentials below 10 mV. The tools are based on the resistive-pulse technique, which uses single pores to probe properties of individual objects including molecules, particles, and cells. The presented experiments were performed with particles 280 and 400 nm in diameter and single pores with opening diameter tuned between ∼ 200 nm and one micron. Surface charge properties were probed in two modes: (i) the passage of the particles through pores of diameters larger than the particles, as well as (ii) an approach curve of a particle to a pore that is smaller than the particle diameter. The curve in the latter mode has a biphasic character starting with a low-amplitude current decrease, followed by a current enhancement reaching an amplitude of ∼10% of the baseline current. The current increase was long-lasting and stable, and shown to strongly depend on the particle surface charge density. The results are explained via voltage-modulation of ionic concentrations in the pore.

Adsorption of poly(acrylic acid) on the surface of microporous activated carbon obtained from cherry stones

The adsorption properties of microporous activated carbon (CSDA) obtained by direct activation of cherry stones in relation to low-molecular weight poly(acrylic acid) − PAA were examined. The solution pH influence and molecular weight of the polymer were examined. The PAA adsorbed amounts were correlated with the solid surface charge density and zeta potential of the solid particle in the polymer presence. The obtained results indicated that the highest adsorption on the activated carbon surface is exhibited by PAA with lower molecular weight at pH 3 (it reaches the level of 25mg/g). Thus, under such conditions the CSDA is the most efficient adsorbent for poly(acrylic acid) removal from aqueous solution. The polymeric adsorption layer at pH 3 is composed of more coiled macromolecules (low degree of PAA carboxyl groups dissociation) which are electrostatically attracted to the positively charged solid surface. It was also proved that applied low-cost activated carbon can be used for removal of undesirable low-molecular polymers from wastewaters.

Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles.

Single pores in the resistive-pulse technique are used as an analytics tool to detect, size, and characterize physical as well as chemical properties of individual objects such as molecules and particles. Each object passing through a pore causes a transient change of the transmembrane current called a resistive pulse. In high salt concentrations when the pore diameter is significantly larger than the screening Debye length, it is assumed that the particle size and surface charge can be determined independently from the same experiment. In this article we challenge this assumption and show that highly charged hard spheres can cause a significant increase of the resistive-pulse amplitude compared to neutral particles of a similar diameter. As a result, resistive pulses overestimate the size of charged particles by even 20%. The observation is explained by the effect of concentration polarization created across particles in a pore, revealed by numerical modeling of ionic concentrations, ion current, and local electric fields. It is notable that in resistive-pulse experiments with cylindrical pores, concentration polarization was previously shown to influence ionic concentrations only at pore entrances; consequently, additional and transient modulation of resistive pulses was observed when a particle entered or left the pore. Here we postulate that concentration polarization can occur across transported particles at any particle position along the pore axis and affect the magnitude of the entire resistive pulse. Consequently, the recorded resistive pulses of highly charged particles reflect not only the particles' volume but also the size of the depletion zone created in front of the moving particle. Moreover, the modeling identified that the effective surface charge density of particles depended not only on the density of functional groups on the particle but also on the capacitance of the Stern layer. The findings are of crucial importance for sizing particles and characterizing their surface charge properties.

Effect of Relaxation on Drag Forces and Diffusivities of Particles Confined in Rectangular Channels

When a particle is moving inside a channel, its hydrodynamic interaction with channel walls increases its drag coefficient, causing a diffusivity reduction. For charged particles moving in an electrolytic solution, there is an additional drag due to the distortion of an electrical double layer caused by particle motion known as the relaxation effect. Effects of relaxation on drag forces on spheres confined in rectangular channels are computed employing perturbations involving particle Peclet number and surface charge densities. Results indicate that confinement amplifies electrokinetic retardation; increasing the relative particle size or decreasing the channel cross section area enhances the relaxation effect. With the relative particle size kept constant, the relaxation effect on the drag exerted on charged spheres in cylindrical pores with its smaller cross section area is stronger than that on charged spheres in rectangular channels and slit pores. However, for certain values of Debye length and particle size, the ratio between excess drag due to relaxation on confined charged spheres and hydrodynamic drag on uncharged spheres confined at the same location is higher for particles in rectangular channels, resulting in higher percentages of diffusivity reduction. Diffusivity reduction due to relaxation of charged particles in square ducts displays a maximum as a function of relative particle size, whereas that of charged particles in rectangular channels with higher cross section aspect ratio increases monotonically as particle size increases.

Fluorine sorption by aluminosilicate-modified diatomite from highly concentrated fluorine solutions: 1. Adsorption equilibrium

The adsorption capacity of natural (D1) and chemically structure-modified diatomite (DMA) in the removal of fluorine ions from highly concentrated fluorine solutions (up to 0.3 mol/L) under static conditions at room temperature is studied. The effect of different parameters—solution pH, initial fluorine concentration, sorbent weight, and particle surface charge density—is examined to determine the adsorption properties of DMA under different process conditions. It is shown that the solution pH plays a crucial role in the removal of fluorine from solutions. An efficient removal of fluorine occurs at a pH of 4.5–5.5. Under equilibrium conditions, upon the saturation of the DMA surface with fluorine ions, the adsorption capacity of DMA achieves 58 mmol/g of sorbent; this value is 5.5 times higher than that of unmodified D1. Fluorine adsorption isotherms for DMA samples are derived; equilibrium adsorption data are modeled using a twostage Langmuir model; it is shown that the experimental and calculated data on fluorine adsorption are in good agreement: correlation coefficient R2 for the D1 and DMA samples is 0.9952 and 0.9687, respectively. The fluorine adsorption mechanism is studied. X-ray diffraction and chemical analyses, FTIR spectroscopy, potentiometric titration, and adsorption–desorption experiments reveal that the diatomite–NaF–H2O system is characterized by the occurrence not only of physical adsorption and ion exchange but also of the chemical bonding of the fluorine ions with the active sites of the sorbent surface, i.e., the formation of weakly soluble fluorine compounds with Al on DMA and with Ca on D1 (AlF3, Na3AlF6, СаF2).

Electrosurface properties of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the Γ H + (pH) and Γ OH - (pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.

Adsorption properties of the nanozirconia/anionic polyacrylamide system—Effects of surfactant presence, solution pH and polymer carboxyl groups content

The adsorption mechanism of anionic polyacrylamide (PAM) on the nanozirconia surface was examined. The effects of solution pH, carboxyl groups content in macromolecules and anionic surfactant (sodium dodecyl sulfate—SDS) addition were determined. The more probable structure of polymer adsorption layer was characterized based on the data obtained from spectrophotometry, viscosimetry and potentiometric titration methods. The adsorbed amount of polymer, size of macromolecules in the solution and surface charge density of ZrO2 particles in the absence and presence of PAM were assessed, respectively. Analysis of these results indicated that the increase of solution pH and content of carboxyl groups in the polymeric chains lead to more expanded conformations of adsorbing macromolecules. As a result, the adsorption of anionic polyacrylamide decreased. The SDS presence caused the significant increase of PAM adsorbed amount at pH 3, whereas at pH 6 and 9 the surfactant addition resulted in reduction of polymer adsorption level.

Nano ellipsoids at the fluid-fluid interface: effect of surface charge on adsorption, buckling and emulsification.

In this contribution, we discuss the role of surface charge on the adsorption of shape anisotropic particles to fluid-fluid interfaces in the context of their application in particle-stabilized emulsions. Starting with a pendent aqueous drop containing nano-ellipsoids of known surface charge density suspended in an oil medium, we study the kinetics of adsorption of the ellipsoids to the water-decane interface using pendant drop tensiometry. The interfacial tension of the drop is recorded as a function of time by analyzing the shape of the drop. We show that the particles that are weakly charged readily adsorb to the water-decane interface and the adsorption behavior is influenced by the particle surface charge density. Furthermore, as the area available for the particles deposited at the interface is reduced, the interface populated with self-assembled ellipsoids shows wrinkles indicating buckling of the particle-laden interface under compression. However, the buckling is not observed if nano-ellipsoids are highly charged confirming that the particles do not adsorb to the interface when they are highly charged. This suggests that in several examples where the particles at interfaces concept is exploited, the repulsive energy barrier due to the particle surface charge plays a key role in the adsorption of particles to the interfaces. However, once the particles are adsorbed, the interfacial properties of the monolayer depend on the particle-particle interactions. Thus a combination of these interactions determines the concentration of particles at the interface, their microstructure and interfacial properties. The effect of these interactions on the quantity and size of the emulsion drops stabilized by ellipsoidal particles is also explored.

The non-dominance of counterions in charge-asymmetric electrolytes: non-monotonic precedence of electrostatic screening and local inversion of the electric field by multivalent coions.

The asymptotic convergence of the thermodynamic and structural properties of unequally-sized charge-symmetric ions in strong electric fields was postulated more than thirty years ago by Valleau and Torrie as the dominance of counterions via the non-linear Poisson-Boltzmann theory [Valleau and Torrie, J. Chem. Phys., 1982, 76, 4623]. According to this mean field prescription, the properties of the electrical double layer near a highly charged electrode immersed in a size-asymmetric binary electrolyte converge to those of a size-symmetric electrolyte if the properties of counterions are the same in both instances. On the other hand, some of the present authors have shown that, in fact, counterions do not dominate the electrical properties of a spherical macroion in the presence of unequally-sized ions, symmetric in valence, if ion correlations and ionic excluded volume effects are taken into account consistently. These ingredients are neglected in the classical Poisson-Boltzmann picture. In the present work, we show the occurrence of the non-dominance of counterions in the opposite scenario, that is, when ions are equally-sized but asymmetric in valence. This is performed in the presence of highly charged colloidal surfaces of spherical and planar geometries for different ionic volume fractions. In addition to the phenomenon of non-dominance of counterions, our simulations and theoretical data also exhibit a non-monotonic order or precedence in the mean electrostatic potential, or electrostatic screening, at the Helmholtz plane of a charged colloid. This interesting behaviour is analyzed as a function of the coion's valence, the ionic volume fraction, and the charge and size of the colloidal particle. All these phenomena are explained in terms of the decay of the electric field near the colloidal surface, and by the appearance of a local inversion of both the electric field and the integrated surface charge density of the colloidal particle in the presence of monovalent counterions and multivalent coions.

Synthetic polyacrylamide as a potential flocculent to remove commercial chromium(III) oxide from aqueous suspension

The effects of solution pH and cationic group contents in polyacrylamide (PAM) macromolecules on the polymer adsorption mechanism on chromium(III) oxide surface were studied. The structure of PAM adsorption layer was also characterized to explain the changes in solid suspension stability. The following methods were applied: turbidimetry, spectrophotometry, potentiometric titration and microelectrophoresis. Thanks to them, the stability of the Cr2O3–polymer systems, polymer-adsorbed amount, surface charge density and zeta potential of solid particles were determined. The experimental results indicate that adsorption of cationic PAM increases with the rising pH. The larger the content of cationic groups in PAM chains is, the higher the adsorption level is observed. The most effective chromium(III) oxide removal is achieved at pH 9 after addition of PAM with the largest content of cationic groups (i.e. 80 %). The neutralization of solid surface negative charge by positively charged polymer chains (assuming more coiled conformation) is responsible for this.

Influence of temperature on adsorption mechanism of anionic polyacrylamide in the Al2O3 –aqueous solution system

The influence of temperature on the adsorption mechanism of anionic polyacrylamide (PAM) on the alumina surface was studied in the temperature range 15–35 °C. The structure of polymer adsorption layer was determined from spectrophotometric, surface charge and zeta potential measurements. These methods enable determination of the following parameters: adsorbed amount of polymer, surface charge density and zeta potential of Al2O3 particles in the absence and presence of PAM. The influence of carboxyl groups content in the polyacrylamide macromolecules (varying from 5 to 50%) was also examined. The obtained results indicate that temperature influences the adsorption behaviour of anionic polyacrylamide on the Al2O3 surface. Slight increase of PAM adsorbed amounts with the temperature rise was obtained for the polymer samples characterized by the higher anionic group content (20, 30 and 50%). In the case of PAM with 5% content of these groups significantly larger adsorption was observed at 25 °C. The PAM presence causes also changes in electrokinetic properties (zeta potential and surface charge density values, as well as pHpzc and pHiep positions) of the examined system in the temperature range 15–35 °C.