Surface Charge Density Of Particles Research Articles

Effect of flow path structure on solid/liquid separation under electric field

Electroosmosis is especially effective in removing liquid from a highly compressible difficult-to-filter solid/liquid mixture. The extent of solid/liquid separation depends on the electroosmotic pressure gradient (Epg) which is a combination of applied electric field, the surface charge density of solid particles and the flow path structure in the mixture. The larger the Epg value, the higher the solid content of the treated mixture. A theoretical equation of Epg for a capillary flow is derived from the Navier–Stokes equation, and its extensions to a flow through porous materials are examined by using experimental Epg values from constant-current electroosmotic dewatering (EOD), electroosmotic permeation (EOP) and electro-forced sedimentation (EFS) tests. It has been clarified that the specific hydrodynamic resistance α has the most effect on the Epg value. The larger the α value of the material, the larger its Epg value. Modifications to the existing theories were suggested to understand the effect of solid/liquid mixture concentration on the separation under electric field more precisely.

Rheology behavior of sulfonate functional Colloidal Unimolecular Polymer (CUP) particles

Colloidal Unimolecular Polymer (CUP) particles were prepared by water-reduction of copolymers of methyl-methacrylate and 2-acrylamido-2-methylpropane sulfonic acid. Absence of additives like surfactant or emulsifier, easy synthesis and controllable particle size in the true-nano region (diameter 3–9nm) make the CUP systems an excellent material to study the electro-viscous effects and the effect of surface water on the rheological behavior of charged nanopolymers. In the dilute concentration regime (volume fraction<0.10), the tertiary electroviscous effects dominated the rheology behavior and the associated water fraction on the surface of sulfonate (SO3−)-CUPs increased with increasing molecular weight or surface charge density of the CUP particles. The SO3−-CUPs had a thicker and a denser surface water layer than the carboxylate (CO2−) functional CUPs.

Lysozyme adsorption on the colloidal chromium(III) oxide surface: Its impact on the system stability

This paper describes the lysozyme (LSZ) presence effect on the chromium(III) oxide (Cr2O3) suspension stability. First, the electrokinetic properties of the examined system, i.e. surface charge density and zeta potential of solid particles in the absence and presence of LSZ, were determined. The lysozyme addition reduces the metal oxide surface charge, which may be related to the interaction of the LSZ protonated amino groups with the adsorbent surface moieties. The LSZ macromolecules undergo adsorption on the Cr2O3 surface only under electrostatic attraction. At the LSZ concentrations above 50ppm the macromolecules cover completely the particle surface, which is evidenced by the observed zeta potential values. The LSZ influence on the Cr2O3 suspension stability depends on the solution pH value. At pH 3, 4.6 and 7.6, the LSZ addition improves the system stability. In turn, at pH 9 it is associated with the slight suspension destabilization.

Biphasic Resistive Pulses and Ion Concentration Modulation during Particle Translocation through Cylindrical Nanopores

We investigated the biphasic resistive pulses during particle translocation through cylindrical nanopores at low salt concentration by simulation, and the effects of electrolyte concentration, surface charge, electric potential, and pore geometry were systematically discussed. The formation of positive peaks in the pulses is ascribed to the surface charge on the particle and the pore. The peak current enhancement/decline ratio increases linearly with the particle surface charge density but decreases with the salt concentration increase. We find that there is an optimum electric potential for the peak current enhancement ratio to reach the maximum value. When a negatively charged particle is at the orifice of the pore on the low/high potential side, the ion concentration inside and around the pore is significantly depleted/enriched, while inverse electric potential or inverse surface charge has an opposite effect. The extent of such ion modulation is larger with a longer pore. The peak current enhancement/decline ratio is quantitatively linked to the percent of ion concentration enrichment/depletion inside and around the pore, by considering particle occupied volume and concentration change.

Synthesis and characterization of cationic colloidal unimolecular polymer (CUP) particles

Cationic colloidal unimolecular polymer (CUP) particles were prepared by using a lower concentration of the quaternary ammonium functional copolymers during the process of water reduction. True nanoscale (diameter 3–9 nm), zero-volatile organic content (VOC), spheroidal CUP particles, and self-stabilized via electro-repulsion of surface cationic groups were obtained. The viscosity of the cationic CUP systems was influenced by the electroviscous effects arising from the surface charge and the associated surface water layer. The density of surface water was 1.6 % greater than the bulk water density which was attributed to the structuring of water around charged quaternary ammonium groups. The equilibrium surface tension values decreased linearly with increasing concentration and surface charge density of CUP particles due to a greater reduction in surface energy. The rate of surface tension reduction determined by maximum bubble pressure method decreased with increasing concentration and the molecular weight of the CUP due to diffusion effects.

Impact of anionic and cationic polyacrylamide on the stability of aqueous alumina suspension—comparison of adsorption mechanism

In the present study, particular emphasis was put on the effects of the type of functional groups of anionic and cationic polyacrylamide (PAM) and solution pH on the mechanism of polymer adsorption on the surface of dispersed alumina. The polymer-adsorbed amount, surface charge density and zeta potential of solid particles without and with PAM, as well as the stability of Al2O3 suspension containing the polymer, were determined. For this purpose, the spectrophotometry, potentiometric titration, microelectrophoresis and turbidimetry were applied. It was shown that adsorption of anionic PAM decreases with the pH rise, whereas in the case of cationic PAM, it increases. High adsorption level is a result of more coiled structure of adsorbed macromolecules. The anionic PAM has greater impact on the suspension stability deterioration in comparison to the cationic polymer in the whole range of studied pH values. The more pronounced effect of alumina suspension destabilization in the anionic PAM presence was obtained at pH 6, at which solid surface charge neutralization occurs.

실리카졸의 표면 전하 밀도와 염료 흡착과의 상관성

In this study, we investigated the relationship between the adsorption property of Methyl violet or Tartrazine dye onto silica sol surface and surface charge density of the sol. The adsorption ratio of Methyl violet dye on silica sol decreased to 74% and 92% for the 68nm and 94nm silica sol, respectively, at dye concentration of 175μg/m 2 . However, the adsorption ratio of Tartrazine dye on 68nm and 94nm silica sol was about 0% for both of them. The surface charge density is 0.40C/m 2 , -0.26C/m 2 for 68nm and 94nm silica sol, respectively. The amount of Methyl violet dye adsorbed on silica sol increased with an increase of surface charge density of particle at the same concentration of the dye. The adsorbed amount of the silica having high surface charge density is larger at high pH domain. But adsorbed amount of the silica having low surface charge density is larger at low pH domain.

Effect of the presence of cationic polyacrylamide on the surface properties of aqueous alumina suspension-stability mechanism

The effects of solution pH and the content of cationic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of aqueous alumina suspension were investigated. The following experimental techniques were applied: spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry. They enable determination of polymer adsorbed amount, surface charge density and zeta potential of solid particles in the presence and absence of PAM, as well as thickness of polymer adsorption layer, size of macromolecules in the solution and stability of the Al2O3–polymer systems, respectively. The obtained results indicate that adsorption of PAM increases with the increasing pH, whereas the thickness of polymeric adsorption layer decreases. Additionally, the greater the number of cationic groups in the PAM chains is, the higher adsorption was found. The polymer presence influences on the alumina suspension stability. At pH 3 and 6 the slight deterioration of stability conditions of solid particle covered with polyacrylamide was observed. At pH 9 the systems containing polymer are unstable, similarly to the suspension without PAM, but the mechanism of their destabilization is different.

Impact of particle size and surface charge density on redispersibility of spray-dried powders

To understand the impact of surface charge density on the redispersibility of spray dried powders, the redispersibility of styrene-butadiene (SB) powders prepared from latexes with various particle sizes and acid contents was investigated. The redispersibility of these powders showed a step function from fully redispersible to non-redispersible. The phase boundary between these two regimes is determined by the product of the latex particle size and acid content, which is strongly related to the surface charge density of the latex particle. Results indicate that to achieve fully redispersible polymer powder, a proper balance of latex particle size and surface charge is needed. For the class of SB latexes studied in this work, with a certain acid level, it is possible to predict the minimum latex particle size that enables redispersibility of its spray dried powder. This phenomenological observation is unique and it may help us to reveal the fundamentals which govern the redispersibility. To maintain the redispersibility of a spray dried powder, a colloidal stabilizer that adsorbs onto the surfaces of latex particles is required. When latexes are brought to close proximity, strong van der Waals forces may deplete the surface stabilizers, causing irreversible latex agglomeration at spray drying temperatures. A qualitative DLVO analysis was employed to study the impact of various colloidal interactions in this system, including van der Waals, electrostatic, and steric interactions. Zeta potential measurements of the mixture of SB latex and polyvinyl alcohol (PVOH, used as a colloidal stabilizer) suggest that the surface charge density plays a significant role on redispersibility, and strong electrostatic repulsive interactions are needed to overcome the attractive van der Waals interaction. Size exclusion chromatography of serum phase analysis indicated that PVOH adsorption onto latex particles did not change significantly at different acid levels, suggesting low impact of steric repulsion on redispersibility. Conclusions from this work provide additional means to control the performance of redispersible materials.

Analysis of electrostatic powder charging for fractionation of foods

Electrostatic separation based on different tribo-electric charging behaviours of components has emerged as a novel, sustainable dry fractionation process. This study aims to characterise charging behaviour of single-component particles in nitrogen gas flowing through aluminium tubes. Experiments were carried out with polystyrene (PS) particles and wheat gluten as model particles. Results indicated that specific charge increased linearly with gas velocity up to 28 m/s for both materials. It was found that surface charge densities of different-sized PS particles overlapped for laminar gas flow, whereas for higher stronger gas flow rates, surface charge density of the smallest particles deviated from that of larger particles. Specific charge of PS particles increased linearly with increasing tube length from 125 to 225 mm. Additionally, charging of PS particles was unaffected by relative humidity (RH) of gas; however, specific charge of wheat gluten decreased for RH > 80%. Concluding, these results provide insight in critical parameters affecting charging behaviour, thus facilitating the development of electrostatic separation processes to fractionate food ingredients.

Characterization of surface charge and zeta potential of colloidal silica prepared by various methods

Colloidal silica is prepared by hydrolysis of TEOS, direct oxidation of Si powder, condensation of silicic acid, etc. There are differences in surface reactivity of silica particle due to the preparation routes. Therefore, it is useful to evaluate surface properties accurately in order to understand the physiochemical properties of the products. The surface charge density, site density and zeta potential with respect to three types of colloidal silica were estimated and discussed. The surface charge density was different depending on preparation method. It is decreasing in the order of direct oxidation, ion exchange, TEOS hydrolysis. The zeta potential is decreasing in the order of ion exchange, TEOS hydrolysis, direct oxidation. The order in surface charge density is different from that in zeta potential because of the difference in stability depending on the particle size and surface charge density.

Analytical model for surface charge property of pH-regulated nanorods

An analytical model for the zeta potential and the surface charge density of pH-regulated nanorod particles is derived for the first time. This extends existing models by taking account of the effects of multiple ionic species, surface chemistry reactions, Stern layer, and surface curvature, all of practical significance. Our model predicts excellently the experimental data in the literature for the zeta potential of 11-mercaptoundecanoic acid functionalized gold nanorod. The validated analytical multi-ion model provides valuable information for applications involving pH-tunable nanorods.

Adsorption of cationic nanospheres on cotton fibers: the effect of emulsifiers used in the cationic emulsion polymerization

Cationic p(St-co-BA) nanospheres were prepared and their adsorption on cotton fibers was carried out. The effect of Gemini emulsifier ethanediyl bis(hexadecyl dimethyl ammonium bromide) (G16-2-16) on the colloidal features and adsorption properties of the cationic nanospheres was investigated. To get a clear understanding, the corresponding single-chain emulsifier hexadecyl trimethyl ammonium bromide (CTAB) was used as a comparison. Colloidal features, such as particle size and surface charge density, and adsorption properties, such as adsorption rate, were measured. G16-2-16 produced cationic p(St-co-BA) nanospheres with bigger particle size, better monodispersity, and higher surface charge density than CTAB. Compared with CTAB, G16-2-16 resulted in higher adsorption rate and more uniform arrangement of nanospheres at the cotton fiber surface.

Modification of the alumina surface properties by adsorbed anionic polyacrylamide—Impact of polymer hydrolysis

The effects of solution pH and degree of polymer hydrolysis on the adsorption mechanism of anionic polyacrylamide (PAM) on the alumina surface were investigated. The spectrophotometry, potentiometric titration, microelectrophoresis and thermogravimetry were applied to determine polymer adsorbed amount, surface charge density and zeta potential of solid particles in the presence and absence of PVA, as well as thermal characteristics of Al2O3 surface with the adsorbed polymer, respectively. The obtained results indicate that adsorption of PAM decreases with the increasing pH. Additionally, the polymer adsorption level depends on its degree of hydrolysis (which is equivalent to the content of carboxyl groups).

Analytical model for charge properties of silica particles

An analytical model for surface charge density and zeta potential of silica particles is derived and verified. The model takes into account surface chemistry reactions of the silanol groups and multiple ionic species. The predictions are in good agreement with the experimental data available from the literature. Surface charge density and zeta potential of silica particles strongly depend on both pH and background salt concentration of the aqueous solution.

Advanced soap-free emulsion polymerization for highly pure, micron-sized, monodisperse polymer particles

A previously proposed method of soap-free emulsion polymerization employing an amphoteric initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] (VA-057), was extended to synthesize micron-sized, monodisperse polystyrene (PSt) particles at low impurity levels. Initial pH values of solutions in which anionic PSt particles were formed were adjusted between neutral pH and 8.9 with a tiny amount of strong base such as NaOH to constitute a low-impurity polymerization system. Micron-sized polymer particles with a narrow size distribution were obtained in a pH range of 8.1–8.9. Different strong bases of KOH, Ca(OH)2 and tetramethylammonium hydroxide were also added to examine electrostatic interaction between PSt particles formed in the low-impurity system, indicating that surface charge density of PSt particles is an important factor to determine size distributions of PSt particles formed. Polymerizations at high styrene concentrations and an appropriate VA-057 concentration succeeded in preparation of highly pure, monodisperse PSt particles with an average size of 1.86 μm.

Novel polyelectrolyte complex membranes containing free sulfate groups with improved pervaporation dehydration of ethanol

Novel polyelectrolyte complexes containing free sulfate (SO3) groups (PECSs) were synthesized, with the sulfation of NH2 groups in the soluble chitosan (CS)/sodium carboxymethyl cellulose (CMC) complexes, and their membranes (PECSMs) were subjected to pervaporation dehydration of ethanol. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the chemical structure and the composition of PECSs. Zeta (ξ) potential and field emission scanning electron microscopy were used to investigate the surface charge density of the PECS particles and the morphology of their membranes. The effects of the chemical composition on the swelling degree, the hydrophilic property, and the pervaporation dehydration performance of PECSMs were determined. It was found that free SO3 groups were successfully incorporated into PECSMs. Both the flux and the separation factor of PECSMs increased with increasing SO3 groups. The permeation flux of PECSMs increased, and their selectivity was almost invariable with increasing temperature. A high separation performance of PECSMs was achieved in the dehydration of 10wt% water–ethanol mixtures at 70°C, yielding a flux and a separation factor for the PECSM-20 at 1385g/m2h and 1571, respectively. These results indicated that the introduction of free SO3 groups into PECSMs was an effective strategy to improve the pervaporation dehydration performance of PECSMs.

Aggregation and Charging Behavior of Polydisperse and Monodisperse Colloidal Epoxy-Amine Adducts

An investigation is presented into the effect of particle size distribution on the aggregation behavior of colloidal dispersions and validity of the Derjaguin-Landau-Verwey-Overbeek(DLVO) theory. The colloidal dispersions of epoxy amine adducts were prepared with various particle size distributions (PSD) and surface charge densities. Moreover, the Fuchs stability ratios W were obtained in aqueous solution with and without consideration of the viscous effects. It was found that PSD of colloidal dispersions affect the reliability of the prediction of DLVO theory. In order to achieve a good agreement between experimental and theoretical critical coagulation concentration (CCC) values of the colloidal dispersions, a new expression with consideration of particle size distribution was introduced.

Effect of Surface Charge Density on the Affinity of Oxide Nanoparticles for the Vapor–Water Interface

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.

Highly charged hollow latex particles prepared via seeded emulsion polymerization

The carboxylated hollow latex (HL) particles possessing high surface charge density were conveniently prepared by using poly(styrene-co-acrylic acid) (P(St/AA)) as seed particles and methyl methacrylate (MMA)/divinylbenzene (DVB)/AA as monomers. Without seed removal, the hollow structure was simply tuned by adjusting the monomer/seed ratio and the monomer content. The monodisperse, spherical, and non-collapsed HL particles with double shell having the void of 280nm were obtained from P(St/AA) seeds of 300nm. The conductimetric back titration, SEM, TEM, and dynamic light scattering measurement revealed that the surface charge density, surface roughness, and size of HL particles significantly increased when applying the stepwise charging monomers/initiator. The highly charged HL particles would be well dispersed in coating film providing good optical properties, for example, opacity and whiteness.