Zeta Potential Of Silica Research Articles

Primary study of synthesis and dispersion of zirconia and silica nanoparticles for post-endodontic composite

Zirconia and silica-based composite are introduced as an alternative to post-core systems due to their high elastic modulus. The cast metal post-core systems in the application of dental material can cause stress concentration within the surrounding radicular dentin, resulting in root fractures. These materials provide more esthetical appealing and biocompatible restorations. However, the use of zirconia and silica nanoparticles as fillers tends to agglomerate in an organic solvent. The objective of the present report is to synthesize zirconia and silica nanoparticles by solgel method and subsequently, disperse them in an organic solvent by beads milling methods. The particle size distribution and stability were observed correspondingly using the particles size analyzer (PSA) and zeta potential. The initial average sizes of silica and zirconia particles in organic media were correspondingly 2.7 mm and 191 nm, respectively. After beads milling for 5 hours, silica and zirconia nanoparticles successfully were dispersed with average particles size of 91.5 nm and 124 nm, respectively. The zeta potentials of silica and zirconia suspensions were - 21.1 and -10.6 mV, respectively. The SEM image for both particles showed spherical morphology with agglomerated particles having primary particle sizes below 100 nm. Therefore, it was concluded that both particles can be applied as filler for a post-endodontic composite with an additional surfactant before polymerization.

Preparation and characterization of modified silica eugenol nanocapsules and their interaction with leather

Aromatic leather products can cover the peculiar smell of traditional leather products. Microencapsulation is the main way of leather perfuming, but the interaction between microencapsulated fragrance and leather is lacking. This study mainly discussed the preparation of a silicon-based fragrance nanocapsules and their interaction with leather. (3-aminopropyl) triethoxysilane (APTES) modified silica nanoparticles (MSN) were prepared by sol-gel method and encapsulated eugenol, and MSN with an average particle size of 328.75 nm was obtained. According to results found that the zeta potential of silica is −38.35 mV, there is a strong electrostatic attraction between it and leather, according to infrared, thermogravimetric analysis, there are hydrogen bonding, van der Waals forces, chemical bonding and other non-covalent forces between them, and the adhesion force was found to be 30.74 ± 1.62 nN by AFM force curve. Combined with the adsorption thermodynamic model, leather has strong adsorption on MSN, and its adsorption behavior is physical adsorption. The introduction of new groups has a positive enhancement effect on the adsorption effect. Therefore, the MSN can be well applied to leather perfuming, to provide new ideas for in-depth understanding of the adsorption behavior and mechanism of action of microencapsulated fragrance in aromatic leather on the leather surface, and promotes the development of aromatic leather.

Electro-osmotic flow of surfactant assisted zeta potential tuned silica frits

The choice of surfactant is vital for tailoring the zeta potential of silica which in turn improves the electro-osmotic performance.

Zeta potential of CO2-rich aqueous solutions in contact with intact sandstone sample at temperatures of 23 °C and 40 °C and pressures up to 10.0 MPa

Despite the broad range of interest and applications, controls on the electric surface charge and the zeta potential of silica in contact with aqueous solutions saturated with dissolved CO2 at conditions relevant to natural systems, remains unreported. There have been no published zeta potential measurements conducted in such systems at equilibrium, hence the effect of composition, pH, temperature and pressure remains unknown.We describe a novel methodology developed for the streaming potential measurements under these conditions, and report zeta potential values for the first time obtained with Fontainebleau sandstone core sample saturated with carbonated NaCl, Na2SO4, CaCl2 and MgCl2 solutions under equilibrium conditions at pressures up to 10 MPa and temperatures up to 40 °C.The results demonstrate that pH of solutions is the only control on the zeta potential, while temperature, CO2 pressure and salt type affect pH values. We report three empirical relationships that describe the pH dependence of the zeta potential for: i) dead (partial CO2 pressure of 10-3.44 atm) NaCl/Na2SO4, ii) dead CaCl2/MgCl2 solutions, and iii) for all live (fully saturated with dissolved CO2) solutions. The proposed new relationships provide essential insights into interfacial electrochemical properties of silica-water systems at conditions relevant to CO2 geological storage.

Analysis of Silica Pulp Viscoelasticity in Saline Media: The Effect of Cation Size

The effect of alkali metal chlorides on the viscoelastic behavior and yielding properties of silica suspensions was studied through creep-recovery and dynamic oscillatory tests with stress control. Then, the viscoelasticity of the pulps was correlated with the silica zeta potential, aggregate size, and the percentage of cations adsorbed on the surface of the ore. The results indicate that larger cations are more prone to adhere to the silica surface, which increases the number of ionic bonds that bind the particles. This generates stronger particle networks and a greater agglomeration of particles, especially those smaller than 10 µm. As the size of the bare cations increases, the rheological response provides higher values of yield stress, complex viscosity, and viscoelastic moduli, but in turn, pulps undergo minor deformations under the application of stress. Dynamic oscillatory tests suggest structural changes, with the phase angle following the inverse relationship with the bare cation size, indicating that the liquid-like character of the pulps increases as the size of the cations increases.

Durability enhancement of a Pt/C electrocatalyst using silica-coated carbon nanofiber as a corrosion-resistant support

Electrochemical oxidation of a carbon support is one of the major challenges to making proton exchange membrane fuel cells (PEMFCs) durable. The aim of this study was to develop a durable carbon-based electrocatalyst support for use in PEMFCs. Platelet-type carbon nanofiber (PCNF) was coated in a uniform and discrete manner with silica by successive hydrolysis of two kinds of silica precursors, APTES and TEOS. The shape and thickness of the silica coating on carbon was controlled by adjusting the amount of APTES and TEOS. The platinum was mainly deposited on silica rather than carbon because the zeta potential of silica is more favorable to binding platinum precursor ions than that of PCNF. Accelerated degradation testing of the silica-coated catalysts (Pt/PCNFSiO2) and Pt/PCNF showed that Pt/PCNFSiO2 possess higher durability than Pt/PCNF under potential cycling. After 30,000 potential cycles ranging from 1.0 V to 1.5 V, the electrochemical surface area losses were 21%, 16%, and 11% and the half-wave potential (E1/2) degradation losses were 16 mV, 9 mV, and 8 mV for Pt/PCNF and Pt/PCNFSiO2 with two different amounts of silica wt%. Silica-coated carbon nanofibers are expected to be a suitable electrocatalyst support for PEMFCs.

Impact of gypsum supersaturated solution on surface properties of silica and sphalerite minerals

In some sulphide mineral flotation operations, the process water contains high concentrations of calcium and sulphate ions that exceed the solubility limit of gypsum. It has been speculated that the gypsum supersaturated process water would lead to precipitation of gypsum which could coat on mineral surfaces by either nucleation or coagulation, resulting in reduced flotation recovery and selectivity. In this study, a laboratory prepared gypsum supersaturated solution is used to represent the gypsum supersaturated process water, the effect of gypsum supersaturated solution on the surface properties of silica and sphalerite minerals was investigated using zeta potential distribution measurements, scanning electron microscope (SEM), X-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), and quartz crystal microbalance with dissipation (QCM-D). Our results show that silica and sphalerite minerals carry identical surface charge (−10mV of zeta potential) in the gypsum supersaturated solution at pH 10 although they are charged differently in simple electrolyte solution at the same pH. Needle shape gypsum precipitates are found in both silica and sphalerite minerals systems conditioned with gypsum supersaturated solution. The gypsum precipitates do not grow on the minerals surfaces but form in the bulk gypsum supersaturated solution. The heterocoagulation between the examined minerals and gypsum particles is insignificant in the gypsum supersaturated solution. It is the high calcium concentration in the gypsum supersaturated solution that has significant effect on the surface properties of silica and sphalerite minerals. The zeta potentials of silica and sphalerite in a 800ppm calcium solution (similar to the calcium concentration in the gypsum supersaturated solution) are similar to those measured in the gypsum supersaturated solutions. Both silica and sphalerite minerals surfaces are indiscriminately coated with calcium. The surface coating of calcium results in the identical surfaces between silica and sphalerite minerals, and ultimately causes problems for the flotation separation of silica and sphalerite.

Manipulating microparticle interactions using highly charged nanoparticles

An experimental study was performed to investigate the potential use of highly charged, spherical nanoparticles to control the forces between spherical microparticles, with the aim of developing novel methods for reversibly controlling the stability of a colloidal dispersion. A specific focus of the project was to determine the degree to which the nanoparticles strongly adsorb to the microparticles, as such adsorption would severely limit reversibly controlling forces and stability. Colloidal probe atomic force microscopy (CP-AFM) was used to measure the force between a silica microparticle and a silica plate in solutions of highly charged polystyrene nanoparticles at varying pH, covering the range over which the silica surfaces were very weakly charged (e.g., pH≤3) to highly charged (e.g., pH 6.0). It was found that except for the highest pH, where the silica zeta potential was approximately −60mV, addition of relatively low concentrations of the nanoparticles (e.g., 0.1% vol.) led to an increased repulsion between the microparticle and plate. This increased repulsion was evident even at pH 4.0 when the fractional surface coverage of the nanoparticles was only 1%. At low nanoparticle concentrations, this force decayed exponentially with a decay length equal to the bulk Debye length, indicating that it was electrostatic in origin. At higher nanoparticle concentrations (1.0% vol.), long-range depletion forces became significant, causing a deviation from the exponential behavior. This increased repulsion did not disappear upon flushing the nanoparticles out of the system, indicating that the nanoparticles were held in relatively deep energy wells. These results suggest that strong adsorption of nanoparticles should be expected in all but the most highly repulsive systems and also illustrate the challenges associated with using charged nanoparticles as a tool for controlling stability.

Surface modification of glass plates and silica particles by phospholipid adsorption

The effect of phospholipid adsorption on the hydrophobicity of glass plates and on the surface charge of silica particles using contact angle and electrophoretic mobility measurements, respectively, was investigated. Deposition of successive statistical monolayers of dipalmitoylphosphatidylcholine (DPPC) on the glass surface showed zig-zag changes of water contact angle, especially on the first few monolayers. This behavior is qualitatively coherent with the oscillations observed in zeta potential values for increasing DPPC concentration. The results indicate that the phospholipid is adsorbed vertically on the plates, exposing alternately its polar head and non-polar hydrocarbon chains in successive layers. On the other hand, experiments conducted on glass plates prior hydrophobized by contact with n-tetradecane suggest that DPPC molecules may to some extent dissolve in the relatively thick n-alkane film and then expose their polar heads over the film surface thus producing polar electron-donor interactions. The effect of both DPPC and dioleoylphosphatidylcholine (DOPC) on the electrokinetic potential of silica spheres confirms adsorption of the phospholipids, leading to a decrease in the (originally negative) zeta potential of silica and even reversal of its sign to positive at acidic pH. Hydrophobic interactions between phospholipid molecules in the medium and those already adsorbed may explain the overcharging. The adsorption of neutral phospholipids may reduce the zeta potential as a consequence of the shift of the electrokinetic or slip plane. The effect is more evident in the case of DOPC, suggesting a less efficient packing of this phospholipid because of the presence of double bonds in its molecule, which in fact is well known.

Preparation of high purity nano silica particles from blast-furnace slag

High purity nano silica was synthesized using acid treatment and surface modification from blast-furnace slag generated in the steel industry. Blast-furnace slag was treated with nitric acid to extract high-purity insoluble silica. Nano silica was then produced using filtration and surface modified by cation surfactant-Cetyltrimethyl Ammonium Bromide (CTAB). The Zeta potential of silica was tested under various alkaline conditions. Synthesized silica remained electronegative throughout the pH range tested and the number of hydroxyl groups existing on the silica surface was highest when the pH was 9. The size of silica particles was smallest when the modification temperature was 60 °C. The average size of silica particles modified with 3 wt% CTAB was 107.89 nm, while the average size of unmodified silica was 240.38 nm. After extracting silica, pH of the remaining solution was adjusted by adding CaO and then highpurity calcium nitrate crystals were extracted using solubility difference. It was found experimentally that enriching the solution to a high specific gravity (1.63–1.65) before crystallization is preferable for efficient calcium nitrate recovery.

Zeta-potentials and enthalpy changes in the process of electrostatic self-assembly of cations on silica surface

Zeta potentials of silica were measured at different pH. With the increment of pH values, zeta potentials increased accordingly, resulting from the increase of the concentration of the negative charges on the silica surface. With further increment of pH values, however, zeta potentials decreased when pH value reached beyond 10.55. When HCl was added into the system to increase pH, negative charges on the silica surface reduced and so the zeta potential decreased. The isoelectric point of silica colloid appeared at pH 2.99. The density of negative charges was also measured in the process of electrostatic self-assembly of nine kinds of cations (LiCl, NaCl, KCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2, AlCl 3, NH 4Cl). The increased ionity and number of charges of cations were favorable for coagulation of silica colloids. Only Al 3+ can make the negative charges positive without causing colloid to coagulate. The changes of enthalpy and Gibbs free energy in the process of electrostatic self-assembly were determined by calorimetry and calculation, respectively. With the decreased disorder and exothermal change, the electrostatic self-assembly of cations on silica surface is regarded as an “enthalpy-driven” reaction.

Viscoelastic and Shear Viscosity Studies of Colloidal Silica Particles Dispersed in Monoethylene Glycol (MEG), Diethylene Glycol (DEG), and Dodecane Stabilized by Dodecyl Hexaethylene Glycol Monoether (C12E6)

Silica dispersions stabilized by a nonionic surfactant, dodecyl hexaethylene glycol monoether (C 12E 6), were studied using rheological measurements. The viscosity-shear rate flow behavior of silica in monoethylene glycol (MEG) is shear thinning at low shear rates, leading to a Newtonian plateau at high shear rates for all dispersions studied. All rheological properties showed an increase above a critical surfactant concentration. The dispersions were stable at low levels of C 12E 6 concentrations because of electrostatic repulsions as deduced from the zeta potentials of silica that were on the order of about -30 to -65 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high-molecular-weight polymers, was observed in MEG. Viscoelatic measurements of silica in monoethylene glycol at various surfactant concentrations showed a predominantly viscous response at low frequency and a predominantly elastic response at high frequencies, indicative of weak flocculation. Instability is explained in terms of hydrophobic and bridging interactions. Restabilization observed at high surfactant concentration was due to the steric repulsion of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion that moderated rheological measurements in glycol media and introduced the charge reversal of silica particles in dodecane.

Dispersion properties of silica particles in nonaqueous media with a non-ionic surfactant, dodecyl hexaethylene glycol monoether, C 12E 6

An experimental programme is described that evaluated the role of charge and steric stabilisation in glycol and dodecane dispersions of colloidal silica particles on addition of trace water and acid. The surfactant used for steric stabilisation was a non-ionic surfactant, Dodecyl hexaethylene glycol monoether, C 12E 6 with a geometric head-to-tail length of 3.85 nm. The study showed using the self-consistent field theory of adsorption (SCFA), electrophoresis and electroacoustic sonic amplitude (ESA), that the C 12E 6 molecules adsorbed with the ethoxy group attached to the silica surface and the alkyl group in the bulk glycol solution. The thickness of the adsorbed layer as estimated from electrophoretic and viscosity measurements was found to be 8 and 10 nm, respectively, indicative of globular aggregation. The dispersions were stable at low levels of C 12E 6 concentrations due to electrostatic repulsions as deduced from the zeta potentials of silica which were of the order of about −30 to −50 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high molecular weight polymers, was observed in MEG. Critical flocculation concentrations of C 12E 6, ϕ floc, increased with decrease in volume fraction of the silica particles in MEG. Instability is suggested to be from bridging interactions. Restabilisation observed at high surfactant concentration was due to steric repulsions of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion which moderated rheological measurements in glycol media and introduced reversal of charge of silica particles in dodecane.

Optimization of High Flow Rate Nanoporous Electroosmotic Pump

We present a theory for optimizing the thermodynamic efficiency of an electroosmotic (EO) pump with a large surface area highly charged nanoporous silica disk substrate. It was found that the optimum thermodynamic efficiency depends on the temperature, the silica zeta potential, the viscosity, the permittivity, the ion valency, the tortuosity of the nanoporous silica but mainly the effective normalized pore radius of the substrate scaled with respect to the Debye length. Using de-ionized water as the pumping liquid, the optimized EO pump generates a maximum flow rate of 13.6ml∕min at a pressure of 2kPa under an applied voltage of 150V. The power consumed by the pump is less than 0. 4W. The EO pump was designed to eliminate any bubble in the hydraulic circuit such that the pump can be operated continuously without significant degradation in the performance.

The Effect of Additives in Post-Cu CMP Cleaning on Particle Adhesion and Removal

The adhesion force of silica particles to Cu films and the role of additives on adhesion and removal of particles have been theoretically and experimentally investigated in citric-acid-based post-Cu chemical mechanical planarization (CMP) cleaning solutions. The zeta potential of silica and Cu slightly increases when citric acid is added due to the adsorption of citrates. Citric acid is adsorbed on silica and Cu surfaces, resulting in more negative charges on these surfaces. The adhesion force of silica particles on Cu decreases as the citric acid concentration increases due to more repulsive electrostatic interaction between surfaces. The addition of benzotriazole in the cleaning solution initially decreases adhesion then increases it at high concentrations due to the change in zeta potentials. The addition of tetramethylammonium hydroxide to citric acid increases the particle adhesion force. However, the addition of results in the lowest adhesion forces. The highest particle removal efficiency is observed when using cleaning solutions that yield the lowest adhesion force. © 2004 The Electrochemical Society. All rights reserved.

Organization of amphiphiles VI. A comparative study of the orientation of polyoxyethylated alkyl phenols at the air‐water and the silica‐water interface

AbstractThe adsorption behavior on silica of a series of polyoxyethylated alkyl phenols of varying hydrophobicities and hydrophilicities was studied by determining the adsorption isotherm along with the zeta potential of silica. An increase in the concentration of each of the surfactants caused the zeta potential to become less negative and ultimately to reach a plateau; similarly, the adsorption isotherm also plateaued. These results were attributed to the flat orientation of the surfactants caused by hydrogen bonding of the oxygen atom of the oxyethylene group with the silanol group of the silica, which led to the formation of a thin oxyethylene layer at the silica‐water interface. This layer masked a constant fraction of the silica surface. A model for the orientation of the surfactants at the silica‐water interface was proposed, based on a “molecular parking area” (i.e., space occupied by the molecule during adsorption at the silica‐water interface) of the surfactants on the silica surface.

Scanning Probe Characterization of Localized pH Changes on a Sapphire Surface in the Presence of an Applied Field

ABSTRACTSingle crystal sapphire substrates were lithographically patterned with a system of parallel platinum electrodes, which were used to manipulate 1.58μm silica particles inplane, in the presence of an aqueous solution. Observation of the motion of these particles revealed the adhesion of some of them to the sapphire surface near the platinum working electrode, even in the range of pH where the zeta potentials of silica and sapphire are of the same sign. This phenomenon suggests the existence of localized differences in pH, attributable to the presence of potential determining ions produced in the faradaic processes occurring at the electrodes during the electrophoretic manipulation of silica particles. Atomic force microscopy (AFM) was used to corroborate this hypothesis, measuring the forces between a silica particle and a sapphire substrate in the presence of an applied field. The resultant force-distance curves demonstrate a change in the interaction forces between particle and substrate as a function of distance from the electrode. Variations in this interaction correspond to localized differences in the zeta potential of the substrate, which, in turn, are related to localized differences in pH. Quantification of these spatial variations in pH as a function of time yields further information about the diffusion of these faradaically produced potential determining ions across the substrate.

Multiinstrument study of the electrophoretic mobility of fumed silica.

Although silica is one of the most common adsorbents, the position of its isoelectric point (IEP) on the pH scale remains an open question. Different values from 1 to 4 have been published, and there is even a controversy about the very existence of the IEP. The discrepancies in the literature are at least partially due to application of different instruments. Different zetameters produce different zeta potentials of silica in the acidic range and different IEP.

Zeta potentials of monodispersed, spherical silica particles in mixed solvents as a function of cesium chloride concentration

Zeta potentials of silica are negative in most mixed solvents (99% organic co-solvent, 1% water), but in t-butanol and pyridine they are positive. When CsCl is added to the suspension as a probe substance, two types of behavior are observed. In solvents of ε>25, the ζ potential asymptotically approaches zero, while in solvents of lower dielectric constant, the sign of ζ potential is reversed to positive at a sufficiently high CsCl concentration, c rev. In order to evaluate the nature of interaction leading to different solvent responses, a range of frequently used solvent scales relating to specific interactions between the components of the system were compared. A moderate correlation was found between c rev for silica and one solvent property alone, and those previously found for anatase, respectively. Using linear combinations of two solvent scales improved the correlation, but it was still not satisfactory. However, considering separately the contributions from both solvent components, a nearly statistically significant correlation was found. The results are evaluated considering the particular behaviour of each solvent group, and the specific influence of the material properties of silica and of possible impurities present in the system.

STUDIES OF ADHESION OF METAL PARTICLES TO SILICA PARTICLES BASED ON ZETA POTENTIAL MEASUREMENTS

The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum.