Zeta Potential Of Silica Particles Research Articles

Zeta Potential of Nanosilica in 50% Aqueous Ethylene Glycol and in 50% Aqueous Propylene Glycol.

A sufficient amount of ionic surfactants may induce a zeta potential of silica particles dispersed in water-glycol mixtures of about 100 mV in absolute value. Nanoparticles of silica were dispersed in 50-50 ethylene glycol (EG)-water and 50-50 propylene glycol (PG)-water mixtures, and the zeta potential was studied as a function of acid, base, and surfactant concentrations. The addition of HCl had a limited effect on the zeta potential. The addition of NaOH in excess of 10-5 M induced a zeta potential of about -80 mV in 50% EG, but in 50% PG the effect of NaOH was less significant. The addition of CTMABr in excess of 10-3 M induced a zeta potential of about +100 mV in 50% EG and in 50% PG. The addition of SDS in excess of 10-3 M induced a zeta potential of about -80 mV in 50% EG and in 50% PG. Long-chained analogs of SDS were even more efficient than SDS, but their application is limited by their low solubility in aqueous glycols.

Structured silica materials as innovative delivery systems for the bacteriocin nisin

Nisin was encapsulated in silica through sol–gel process by acid-catalyzed routes. The silica xerogels were characterized through nitrogen adsorption isotherms, small-angle X-ray scattering (SAXS), zeta potential, X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy (FTIR). SAXS results showed that the particle diameters in a second level of aggregation varied from 4.78 to 5.86 nm. Zeta potential of silica particles were from −9.6 to −25.3 mV, while the surface area and pore diameters ranged from 216 to 598 m2 g−1 and 2.53 to 2.90 nm, respectively, indicating the formation of mesoporous nanostructures. Nisin retained the antimicrobial activity against all microorganisms tested after encapsulation in silica materials. These novel silica-based structures can be valuable carriers for nisin delivery in food systems.

Yield stress of mixed suspension of silica particles and lysozymes: The effect of zeta potential and adsorbed amount

To investigate the interactions between colloidal particles in the presence of oppositely charged proteins, the yield stress of a mixed suspension of silica particles and lysozymes was measured as a function of lysozyme dose and pH. Further, the corresponding surface properties of silica particles covered with lysozymes were determined by measuring the adsorbed lysozyme amount and zeta potential. The present results indicated that an increase in the adsorbed lysozyme amount increases the zeta potential of silica particles from negative to positive through an isoelectric point. As expected from the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, the maximum value of yield stress is obtained around the isoelectric point and the yield stresses decrease with an increase in the zeta potential magnitude. However, the maximum yield stress depends on the pH, and yield stresses at the same zeta potential magnitude are different depending on the zeta potential sign even if the pH values are similar. That is, the relationship between yield stress and zeta potential is asymmetric with respect to the isoelectric point. These asymmetric results of the yield stress indicate the existence of non-DLVO forces, such as patch-bridging attraction and lateral repulsion between adsorbed lysozymes, affected by the adsorbed amount of lysozyme. Our analysis suggested that the relative adsorbed amount, defined as the ratio of the adsorbed amount to the maximum adsorbed amount, can be used as a parameter to explain the asymmetric feature of the yield stress with respect to the zeta potential. In addition to the zeta potential, the surface occupation of adsorbed substances is critical in controlling particle–particle interactions.

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.

Wetting and electrokinetic properties of cholesterol—Revisited

The important role of cholesterol in human body is well known. Therefore its properties have been investigated in many aspects. However, still some of its surface physicochemical properties are not well understood. Among them are wetting and electrokinetic properties. Therefore the aim of this paper was to study these properties and to compare them with the published literature data. For this purpose the advancing and receding contact angles of water, formamide and diiodomethane on the surface of cholesterol pellets and on its layers deposited on glass from its solution in chloroform were measured and then the surface free energy γS of the layers was calculated from van Oss’ (LWAB) and Chibowski's (CAH) models. Also the images of the surfaces from SEM, confocal and optical microscopes, and profilometer were obtained. It was found that the surface of cholesterol pellets is more hydrophobic than this of the deposited layers, even if up to 200 statistical monolayers have been deposited on glass surface. From the images it was seen that the deposited layers were not uniform and at a larger coverage the needle-like cholesterol crystals were formed on the surface. From the zeta potential of cholesterol as a function of pH in 10−3M NaCl was found that cholesterol shows the isoelectric point at pH 2.65, which is within the range of the literature data 1.8–3. The hydroxyl ions OH–are the potential determining and probably adsorb on OH groups of cholesterol molecules. In the pH range 3–6 the literature and our results of the negative zeta potential of cholesterol are convergent, except for those measured on a cholesterol suspension precipitated in water from its solution in 1-propanol. The zeta potential of silica particles covered with statistical monolayer of cholesterol lie between those of pure silica and cholesterol suspensions. The calculated electrokinetic charge at the cholesterol surface is very low, e.g. at pH 11, where ζ=−50mV, it amounts one excess negative charge (OH−ion) on the surface of 73 cholesterol molecules (σd=0.422μC/cm2). The results obtained in this paper partially confirm those obtained previously and bring new insight into the structures of cholesterol layers deposited on glass.

粒子表面物性を利用した微粒子分級システムの開発

This study introduces a novel classification system on the basis of particle surface properties. We focused our attention on the zeta potential of silica particles dispersed by beads milling. As a result, it was found that the zeta potential of the particles was enhanced as the particle size became smaller, therefore indicating size dependency. We succeeded in developing a classification apparatus using electrophoresis. This apparatus is able to classify sub-micron sized silica particles with continuous operation and a low running cost.In the case of a dry-cyclone, classification performance was improved by preparing an acetone solution in the dust box of the cyclone to make an acetone vapor in the cyclone. Under these conditions, the ratio of the mass of the powders collected by the upper part of the cyclone to the mass of the total feeding powder was enhanced. One of the reasons for this was the attractive force between the silica particles and the wall of the cyclone resulting from static electricity. Therefore, the cut size was controllable by changing the amount of acetone in the dust box of the dry-cyclone.

Classification of Submicron Silica Particles Using Electrophoretic Phenomenon

The effect of pH, and the concentration of KNO3 and LiNO3 on the electrophoretic mobility and zeta potential of fine silica particles having a different median particle size were studied in order to classify submicron silica particles by electrophoretic phenomenon. The silica particles of 0.05 μm or abradant silica particles (median diameter: 0.067 μm) and silica particles of 0.5 μm were classified by a batch and continuous classification equipment designed in our laboratory. The absolute values of electrophoretic mobility and zeta potential of silica particles are found to be increased with increasing pH. Electrolytes containing cations with different hydration number were added to the particles of 0.05 and 0.5 μm. The electrophoretic mobility of 0.05 μm particles in KNO3 solution is higher than that in LiNO3. On the other hand, electrophoretic mobility of 0.5 μm particles has almost the same value by the addition of two kinds of electrolytes. These results imply that electrophoretic effect works to smaller particles, while do not act large particles. The electrophoretic mobility decreases when the particle size becomes smaller because of strongly acting asymmetric effect and electrophoretic effect. On the other hand, the electrophoretic mobility decreases with increasing a particle size due to the resistance force with viscosity, when the particle size is larger than 1 μm. It is found that the electrophoretic mobility of particles mainly depends on the particle size. In the case of a batch type classification equipment, classification of fine and coarse particles is advanced by applying weak electric field for long period. Classification of fine and coarse particles with a continuous classification equipment shows the possibility of classification using electrophoretic phenomenon.

Characteristics of Zeta Potential Distribution in Silica Particles

Most experimental studies available in the literature on filtration are based on observed average zeta potential of particles (usually 10 measurements). However, analyses of data using the average zeta potential alone can lead to misleading and erroneous conclusions about the attachment behavior because of the variation of particle zeta potentials and the heterogeneous distribution of the collector surface charge. To study characteristics of zeta potential, zeta potential distributions (ZPDs) of silica particles under 9 different chemical conditions were investigated. Contrary to many researchers’ assumptions, most of the ZPDs of silica particles were broad. The solids concentration removal was better near the isoelectric point (IEP) as many researchers have noticed, thus proper destabilization of particles is very important to achieve better particle removal in particle separation processes. While, the mean zeta potential of silica particles at a given coagulant dose was a function of particle concentration; the amount of needed coagulant for particle destabilization was proportional to the total surface charge area of particles in the suspension.

Particle formation in the hydrolysis of tetraethyl orthosilicate in pH buffer solution.

Particle formation in the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) was studied by varying pH (9.5-11) with the basic catalysts NH3, methylamine (MA), and dimethylamine (DMA) in the presence of 5 mol/m3 CH3COOH, which was chosen to suppress time variations of pH and ionic strength during the reaction. Spherical particles were formed for MA and DMA at catalyst concentrations of 0.02-0.2 kmol/m3 and for NH3 at catalyst concentrations of 0.1-1.5 kmol/m3. In a common range of catalyst concentrations for spherical particle formation, average particle size was largest for DMA and smallest for NH3. Hydrolysis rate of TEOS could be quantified by the use of buffer systems as a function of TEOS and OH- concentrations. A specific relation was not found between the hydrolysis and the particle size. The zeta potential of silica particles measured in the reaction solvent was in the order DMA < MA < NH3, and ionic strength, estimated from pH in the reactions, was in the order DMA approximately equal to MA > NH3. This suggested that the particle sizes were controlled by electrostatic particle interactions.

Post cleaning of chemical mechanical polishing process

We describe a study on the effect of the electrostatic nature in silica particles on the post CMP cleaning behavior. A fall-off for the zeta potential of silica particles is observed as the pH of dip solutions is increased. In this study, we also observed that particle counts on the SiO 2 and the Si 3N 4 dielectric films had a similar dependence on the pH. Furthermore, we confirmed that surface hardness of the wafer is an important factor for particles physically embedded in different dielectric materials during and after the CMP process. The nanoscale surface hardness of dielectric films was measured by the nanoindentation technique. Experimental results showed that particles had difficulty attaching to a harder surface of the dielectric film.

Three-Dimensional Particle Tracking for the Characterization of Micrometer-Size Colloidal Particles

A simple technique based on microscopy and computer digitalized images is used to record the three-dimensional trajectory of colloidal particles. The vertical motion is controlled with the help of a piezoelectric actuator and a procedure has been developed in order to keep the particle in the focal plane. This technique allows one to obtain simultaneously the hydrodynamic radius and the density of a particle by following both the Brownian motion and the sedimentation. A demonstration of the capability of the method is given for micrometer-size latex particles. With semitransparent electrodes it is also possible to determine the electrophoretic mobility of a particle. We show that this determination is more accurate than using electrophoretic light scattering when the particles have a low mobility. We apply this technique to determine the diameter, the density, and the zeta potential of silica particles in silicone oil.

Effect of adsorption of non-ionic surfactant and non-ionic—anionic surfactant mixtures on silica—liquid interfacial properties

Adsorption of non-ionic surfactants and non-ionic—anionic surfactant mixtures is shown to have marked effects on silica—liquid interfacial properties such as hydrophobicity and zeta potential. The hydrophobicity of silica surface is found to be dependent on both adsorption density and structure of the non-ionic surfactants. At relatively low adsorption densities, non-ionic surfactant with long ethoxyl chain (C 8φEO 40) is observed to impart hydrophobicity to silica surface, but further adsorption restored hydrophilicity to the silica surface. Such changes in hydrophobicity are not observed with non-ionic surfactant with shorter ethoxyl chain and this difference in hydrophobicity effects is related to the conformational behavior of the adsorbed molecules. Anionic surfactant, which by itself does not adsorb on silica, shows significant adsorption in the presence of the non-ionic surfactant and markedly changes the zeta potential of silica particles. Surfactant adsorption mechanisms responsible for changes in silica—liquid interfacial properties are discussed in this paper.