Silica Particles In Solutions Research Articles

Electrodeposition of bismuth telluride thin films containing silica nanoparticles for thermoelectric applications

The electrodeposition of bismuth telluride (Bi2Te3) with incorporated silica nanoparticles (diameter = 16 nm) was studied in ethylene glycol using a rotating disk electrode. "By matching the refractive index of the silica nanoparticles to the refractive index of the electrolyte i.e. "refractive index matching", the attractive van der Waals force between particles was minimized. Refractive index matching was used to avoid agglomeration of the silica particles in solution due to the attractive van der Waals forces and resulted in Bi2Te3 coatings that contain up to 8vol% of individual silica particles as verified by TEM. The concentration of the incorporated silica nanoparticles was found to be influenced by several parameters: the applied current density, rotation speeds and silica concentration in the electrolyte. A model was developed to predict the amount of incorporated particles. The effect of each parameter was predicted by this model and verified experimentally. The Seebeck coefficient and thermal diffusivity of bismuth telluride films with and without silica nanoparticles were measured.

Interactions between silica particles in the presence of multivalent coions.

Forces between charged silica particles in solutions of multivalent coions are measured with colloidal probe technique based on atomic force microscopy. The concentration of 1 : z electrolytes is systematically varied to understand the behavior of electrostatic interactions and double-layer properties in these systems. Although the coions are multivalent the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory perfectly describes the measured force profiles. The diffuse-layer potentials and regulation properties are extracted from the forces profiles by using the DLVO theory. The dependencies of the diffuse-layer potential and regulation parameter shift to lower concentration with increasing coion valence when plotted as a function of concentration of 1 : z salt. Interestingly, these profiles collapse to a master curve if plotted as a function of monovalent counterion concentration.

Development of a silica sol reinforced monetite cement matrix

The objective of this work is to develop silica sol reinforced monetite cement matrix and study the related reinforcement kinetics. Preparation of monetite cement powder was done using a microwave processing method with active Ca2+ present on particles surface as effective silica bonding sites. The incorporated silica sol significantly improved the compressive strength of the final matrix. It was noted surface areas of silica particles in solution together with the solution concentration were the main factors influencing reinforcement level. In vitro bioactivity and biodegradation indicated silica sol can be a beneficial additive to bone cement.

Adsorption of gold on albite in acidic chloride media

The ability of albite, an aluminosilicate mineral typical of those present in many gold ores, to adsorb gold is examined at varied pH levels in chloride media. The adsorption of gold on albite is intimately associated with the leaching behaviour of albite in acidic solutions. The preferential leaching of Na and Al from albite leads to the formation of an altered silica-rich surface layer as the gold sorbent. Gold adsorption increases at lower pH due to a greater extent of albite leaching. The majority of gold adsorption onto albite occurs within the first 0.5h of contact, and the gold concentration in solution then increases after an extended contact period due to the partial relocation of the adsorbed gold from the altered albite surface to freshly formed nanoscale silica particles in solution. Surface activation by fine milling increases the extent of gold adsorption on albite, correlated with enhanced leaching of albite. The gold adsorbed on processed albite surface exists as Au3+, Au+ and Au0, indicating the reduction of Au3+ in chloroauric acid to lower oxidation states in the silica-rich layers during adsorption.

Scalable PEO-PPO-PEO triblock copolymer purification from Pluronics through competitive adsorption

A new scalable method for large scale purification of Pluronic block copolymers has been developed using a slurry of cyano(CN)-modified silica particles and Pluronic block copolymers in a solution. We have taken advantage of the competitive adsorption of polymers onto nanoporous CN-modified silica particles in solution to purify polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymers from as-received (AR) Pluronic samples, such as F108, F127 and F68. Interaction chromatography and size exclusion chromatography revealed that significant levels of low molecular weight (MW) impurities exist in AR Pluronics. We found that more than 20 wt.% impurities exists in AR F108 and AR F127, while the purified PEO-PPO-PEO triblock copolymers contained less than 2 wt.% of the low MW impurities after using the silica slurry method. In the case of AR F68, which contains about 9 wt.% impurities, it is possible to completely remove the low MW impurities. A multiple injection interaction chromatography technique has been employed to reveal the surface displacement of pre-adsorbed low MW impurities by the triblock copolymers in solution. By tuning the solvent quality, this report finally highlights that the impurities can be effectively removed in laboratory for a large scale purification using the silica slurry. For example, using about 10 g of the bulk silica packing material, it was possible to obtain 1 g of purified triblock copolymers.

Characterisation of silica nanoparticles prior to in vitro studies: from primary particles to agglomerates

The size, surface charge and agglomeration state of nanoparticles under physiological conditions are fundamental parameters to be determined prior to their application in toxicological studies. Although silica-based materials are among the most promising candidates for biomedical applications, more systematic studies concerning the characterisation before performing toxicological studies are necessary. This interest is based on the necessity to elucidate the mechanisms affecting its toxicity. We present here TEM, SAXS and SMPS as a combination of methods allowing an accurate determination of single nanoparticle sizes. For the commercial material, Ludox TM50 single particle sizes around 30 nm were found in solution. DLS measurements of single particles are rather affected by polydispersity and particles concentration but this technique is useful to monitor their agglomeration state. Here, the influence of nanoparticle concentration, ionic strength (IS), pH and bath sonication on the agglomeration behaviour of silica particles in solution has been systematically investigated. Moreover, the colloidal stability of silica particles in the presence of BSA has been investigated showing a correlation between silica and protein concentrations and the formation of agglomerates. Finally, the colloidal stability of silica particles in standard cell culture medium has been tested, concluding the necessity of surface modification in order to preserve silica as primary particles in the presence of serum. The results presented here have major implications on toxicity investigations because silica agglomeration will change the probability and uptake mechanisms and thereby may affect toxicity.

Immobilization of the restriction enzymesHaeIII andHindIII on porous silica particles via a glutaraldehyde linkage for the micro-digestion of dsDNA with analysis by capillary electrophoresis

Solid-Phase DNA restriction digest reactors have been developed consisting of silica particles modified with a covalently tethered restriction enzyme. This solid-phase restriction reactor enables digestion and separation of minute quantities of DNA with minimal reagent consumption. In this study, the restriction enzymes, HaeIII, PstI, and HindIII, were successfully immobilized via glutaraldehyde linkages to porous silica micro-particles. Studies were carried out to examine the impact of immobilization on enzymatic activity. Digestions of ϕX174-RF DNA phage and SV40 viral DNA were performed with the immobilized enzymes by placing the silica particles in solution with the target DNA with digestion times of 120 min and 240 min respectively. The digests were analyzed off-line using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Timed studies were performed to establish optimal conditions for complete digestion. Digests utilizing immobilized HaeIII and HindIII were similar in composition to homogeneous, free solution digests. PstI showed no evidence of activity upon immobilization. The immobilized restriction enzymes could also be used for multiple rounds of digestion; however, longer incubation times were required for successive runs probably due to partial denaturation of the restriction enzyme. Digests also were prepared and isolated by use of a simple micro-spin column consisting of a layer of immobilized enzyme-coated silica on a molecular weight cut-off filter. Using this approach, digestion times were comparable to solution digests as previously mentioned; however, enzyme reuse and reaction product isolation was facilitated.

Proposed mechanism of C-S-H growth tested by soft X-ray microscopy

The reaction of silica particles in solutions saturated or supersaturated with respect to portlandite is observed by transmission soft X-ray microscopy, and a model for calcium silicate hydrate (C-S-H) growth is proposed which corresponds with the morphology observed in the X-ray images. These images show a product that consists of bundles of dendrites that appear to diverge as the growth process continues, resulting in the formation of a characteristic morphology which is narrowest in the middle and broadened at the end — the “sheaf-of-wheat” morphology. In many cases, the dendrites appear to be oriented about a common axis, and it is proposed that this axis corresponds to a common origin in a single crystalline nucleus.

Small-angle neutron scattering from silica particles in solution with different concentrations

The effect of concentration of silica particles in hydrogenated solutions on the small-angle neutron scattering was investigated in the scattering vector range between 6.3 × 10 3 and 3.5 × 10 −1 åA −1. The samples were prepared with volume concentrations from 0.3 up to 16.3%. The experimental data show interference of the scattered neutrons, whose peak shifts towards higher Q values with increasing concentration. The form factor of the silica particle population was determined and, from this, the structure factor was extracted, from which the effective reduced pair correlation functions for the silica particles could be evaluated. Ordering effects of silica particles at various concentration were studied in hydrogenated solutions by SANS.

Layer by Layer Deposition of 5–50-nm Colloidal Silica Particles Studied by Quartz Microbalance

The adsorption on a gold surface of 5–50-nm silica particles in solution has been studied by the piezoelectric quartz crystal microbalance technique. The parameters of the solution where a reproducible layer by layer deposition is possible have been characterized. The uptake depends strongly on the ionic strength of the solution, but only weakly on the particle size or concentration. The strong dependence on ionic strength is attributed to electrostatic screening.

NMR investigations of the silanophilic interactions of alkyl-modified silica

The 13C NMR spin lattice relaxation times have been measured for suspensions of chemically bonded silica particles in solutions of an organic base in deuteroacetonitrile, CD3CN, at different base concentrations. A correlation has been observed between the relaxation rates and the ratio of the amounts of base and silica in the suspension. Thus, silanophilic interactions of chemically bonded silicas can be monitored using 13C NMR relaxation rates. The correlation is interpreted in terms of the rapid exchange model. The method seems to have potential for the rapid and accurate determination of equilibrium isotherms.

Light scattering of silica particles in solution

Static and dynamic light scattering techniques were used to study aggregation of monodisperse silica microspheres prepared by the Stoeber process. The results show that the Stoeber particles form spheroidal aggregates when dispersed in water solutions. In acidic conditions these aggregates tend to coalesce in polydisperse collections of aggregates. These observations are compared with previous works on silica aggregates prepared by different techniques.

Interactions in mixtures of colloidal silica spheres and polystyrene molecules in cyclohexane: II. Light scattering

Light scattering measurements have been conducted on homogeneous systems containing lyophilic, spherical silica particles and polystyrene molecules in cyclohexane at the theta temperature. From the decrease in the apparent molar mass of the silica particles in solutions with increasing concentrations of polystyrene, the negative adsorption of polystyrene on silica was obtained. The negative adsorption, which is caused by the volume restriction effect, increases with increasing molar mass of the polymer. The negative adsorption can be converted formally to an equivalent depletion layer surrounding the particles, in which essentially no polymer is present. The thickness of this layer proves to be comparable with the radius of gyration of the polymer molecules. The apparent optical radius of gyration of the silica particles decreases with increasing polymer concentration and polymer molar mass. This observation is also explained by a negative adsorption of polymer molecules. Calculations show that the decrease in the optical radius of gyration is in agreement with the magnitude of the negative adsorption determined from the apparent molar mass of the silica. The second virial coefficient of the silica particles, determined from the concentration dependence of the light scattering, can become negative, reflecting an effective attraction between the particles. This attraction has been predicted theoretically and can result in phase separation at higher concentrations of polymer.