Presence Of Colloidal Silica Research Articles

Insights into the behavior of ethylene oxide-1,2-epoxybutane diblock copolymers in water as a function of temperature and the presence of colloidal silica

HypothesisNonionic surfactants have been widely used for many consumer products and industrial processes, and their applications often involve temperature-cycling across cloud point temperature (Tcloud). To explore the behavior of nonionic surfactants across Tcloud and when mixed with colloidal silica at a very dilute concentration around 0.1 wt%, a series of 1,2-epoxybutane-capped alcohol ethoxylates (BAEs) with various cloud points is used as a model system. ExperimentsBAEs with cloud points from 15 to 64 °C were successfully prepared by varying the lengths of 1,2-epoxybutane (BO) and ethylene oxide (EO) blocks and their phase behavior across Tcloud was studied using nuclear magnetic resonance spectroscopy (NMR), dynamic light scattering (DLS) and differential scanning calorimetry (DSC). FindingsIn the absence of silica, the NMR signals are not greatly affected by the cloud point transition, but both the water and surfactant exhibit a decrease in spin-spin relaxation time once the temperature reaches the Tcloud. In the presence of silica, the NMR spectra indicate significantly reduced mobility of the EO portion relative to the alkyl and BO segments. Furthermore, our results suggest that the BAE surfactants are not fractionally clouding out or precipitating with a portion of the compositional distribution during the cloud point transition.

Different roles of silica nanoparticles played in virus transport in saturated and unsaturated porous media

Because of the complexity of contaminants infiltrating groundwater, it is necessary to study the co-transport of contaminants in the vadose and saturated zones. To investigate the role of inorganic colloids in the transport of biocolloids through porous media, a series of experiments were performed using columns packed with sand. The Escherichia coli phage (E. coli phage) was used as the model virus and silica as the model colloid in this study. The model virus exhibited a higher degree of attachment when compared with silica under similar experimental conditions. Under unsaturated flow conditions, the degree of virus retention was higher than in the corresponding saturated flow case, regardless of the presence of silica. Mass recovery and breakthrough curve data showed that silica hindered virus transport in saturated porous media. The model virus exhibited a higher degree of retention in the presence of silica. This could be related to pore structure changes caused by aggregated virus-silica particles located within the pores of the sand. Conversely, the suspended virus retained at the air-water interface provided new retention sites for other colloids; the retention was observed to be higher in the presence of colloidal silica in the saturated columns. In the corresponding unsaturated experiments, silica was observed to play the opposite function with respect to virus transport, which demonstrated that silica facilitated virus transport in the presence of unsaturated porous media. Capillary forces were stronger than the virus-silica interactions, and inhibited the aggregation of particles. Suspended silica competes with the virus for sorption sites because of a high affinity for the air-water interface. This competition inhibits virus retention by electrostatic repulsion of like-charged particles, and concomitantly facilitates virus transport under unsaturated conditions.

Spherical Crystalline Anti-Retroviral Drug Particles with Tunable Microstructure

The crystallization of molecular solids is ubiquitous in various contexts, and forms the basis of pharmaceutical drug product design and manufacture. As drug molecules get more complex, their crystallization into well-controlled crystal forms becomes more challenging yet unquestionably important, from a process and product perspective. Here, we demonstrate the fabrication of molecular solids with exquisitely tunable crystalline microstructure by co-confinement of a highly supersaturated drug–colloidal dispersion within submillimeter droplets. Specifically, we show the evaporative solidification of an anti-retroviral drug molecule (Lamivudine, 4-amino-1-[(2R,5S)-2-(hydroxymethyl)-1,3-oxathiolan-5-yl]-2(1H)-pyrimidinone) into spherical crystalline particles in the presence of colloidal silica or polystyrene, where we are able to tune the crystalline microstructure of the drug at the submicron level by using various colloid sizes. Confinement of the drug within droplets generated in a microfluidic device ena...

Preparation and Evaluation of Lipid-Based Liquid Crystalline Formulation of Fenofibrate.

Background:Many drugs have poor water solubility and so the oral delivery of such drugs is usually associated with limitation of low bioavailability and lack of dose proportionality. Lipid-based liquid crystal (LC) systems are excellent potential formulations for increasing dissolution and bioavailability of drugs. The aim of the present study was to formulate lipid-based LC containing fenofibrate (FFB) as a hydrophobic drug.Materials and Methods:The studied variables included lipid and stabilizer concentrations and the type of stabilizer. The LC formation was identified by the polarized optical microscopic method. The effects of variables on formulation characteristics such as particle size, drug release, and rheological behavior were evaluated.Results:The results showed that the prepared formulations had the particle size between 42 and 503 nm. The drug release profiles showed that FFB had the continuous release from the formulations and the highest dissolution efficiency was seen in formulation prepared by 1.5% of glyceryl monostearate and 0.5% of Pluronic F127 as the stabilizer. The change of stabilizer type from colloidal silica to Pluronic F127 increased the drug release, significantly.Conclusions:In the most formulations of FFB LCs, the DE% was more than the pure drug, and therefore, it seems that the liquid crystalline formulations can be effective for enhancing drug release. Furthermore, drug release rate depended on the stabilizer type so that the presence of colloidal silica caused slower drug release compared to Pluronic F127.

EPD 방법을 이용한 알루미나-실리카 복합 코팅막의 제조와 전기절연 특성

Alumina-silica composite coating layers were prepared by electrophoretic deposition (EPD) of plate-shaped alumina particles dispersed in a sol-gel binder, which was prepared by hydrolysis and the condensation reaction of methyltrimethoxysilane in the presence of colloidal silica. The microstructure and the electrical and thermal properties of the coatings were compared according to the EPD process parameter: voltage, time and the content of the plate-shaped alumina particles. The electrical insulation property of the coatings was measured by a voltage test. The coatings were prepared by EPD of the sol-gel binder with 5-30 wt% plate alumina particles on parallel electrodes at a distance of 2 cm for 1-10 min under an applied voltage of 10-30 V. The coatings experienced increased breakdown voltage with increasing thickness. However, the higher the thickness was, the smaller the breakdown voltage strength was. A breakdown voltage as high as 4.6 kV was observed with a 400 μm thickness, and a breakdown voltage strength as high as 27 kV/mm was achieved for the sample under a 100 μm thickness.

Improving manufacturability of an ibuprofen powder blend by surface coating with silica nanoparticles

Using a representative powder blend containing ibuprofen, the applicability of coating with silica nanoparticles using a dry comilling process to effectively enhance flowability of formulated pharmaceutical powders was investigated. Using a shear cell, we systematically studied effects of process parameters, including the total number of comilling cycles, silica loading level, type of screen (mesh size), impeller speed, and impeller type, on the efficiency of the nanocoating process. Impact of silica coating on powder tabletability was also assessed using a compaction simulator. Results confirm that coating with silica nano particles significantly improves flowability of the formulated ibuprofen blend. The two most prominent factors that lead to flowability improvement are 1) repeated comilling cycles and 2) higher silica loading. In addition, we have observed that simple blending is effective in coating silica nanoparticles to improve flowability of the formulated ibuprofen powders, which is not very cohesive. This suggests the possibility of improving flowability of a sub-optimum formulation by prolonging the blending process in presence of colloidal silica. Moreover, silica coated ibuprofen blend exhibits improved tabletability and compactibility without significantly impacting compressibility. The simultaneous improvement in powder tabletability and flowability shows the potential of the nanocoating strategy in improving tablet manufacturability of pharmaceutical powders.

Porous TiO2 microspheres with tunable properties for photocatalytic air purification

The synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa).

Polymerizable nanoparticulate silica‐reinforced calcium phosphate bone cement

Bone cements based on calcium phosphate powder and different concentrations of colloidal silica suspensions were developed. Setting time and washout behavior of the cements were recorded and compared with those of a control group prepared by the same powder phase and distilled water as liquid. The phase composition, compressive strength, and morphology of the cements were determined after incubation and soaking in simulated body fluid. Proliferation of osteoblasts seeded on samples was also determined as a function of time. The results showed that the long setting time, poor compressive strength, and undesirable washout behavior of the cement made with distilled water were considerably improved by adding colloidal silica in a dose-dependent manner. On the basis of XRD and SEM results, both control group and nanosilica-added cements composed of nanosized apatite flakes after 7 days soaking, in addition to tetracalcium phosphate residual for the latter. It was found that the rate of hydraulic reactions that are responsible for conversion of the cement reactants to nanostructured apatite was increased by the presence of colloidal silica. Furthermore, the osteoblasts exhibited better proliferation on nanosilica added cements compared to control one. This study suggests better applied properties for nanosilica-added calcium phosphate cement compared to traditional cements.

Synthesis of polysiloxane-modified silica hybrid particles by a high temperature water technology

Polysiloxane-modified silica hybrid particles were synthesized by hydrolysis and subsequent polycondensation of phenyltrimethoxysilane in the presence of colloidal silica at above 220 °C. The process variables include pH of the colloid, [silica]/[phenyltrimethoxysilane] molar ratio, reaction temperature, and reaction time. The products were characterized by solvent extraction, TGA, GPC, TEM, and 29Si NMR. The degree of surface modification (DOM) ranged between 5 and 35 wt.% by tuning the process variables when a neutral colloid was used. On the other hand, the DOM proved to be strongly dependent on temperature and becomes essentially zero when the synthesis was conducted with an acidic colloid at temperatures as high as 350 °C. TEM analysis suggested that each silica particle was surface modified resulting in minimal aggregation of the particles. The hybridization mechanism was studied by the DOM and the molecular weight of ungrafted polysiloxane.

Spray-drying Nanocapsules in Presence of Colloidal Silica as Drying Auxiliary Agent: Formulation and Process Variables Optimization Using Experimental Designs

Spray-drying process was used for the development of dried polymeric nanocapsules. The purpose of this research was to investigate the effects of formulation and process variables on the resulting powder characteristics in order to optimize them. Experimental designs were used in order to estimate the influence of formulation parameters (nanocapsules and silica concentrations) and process variables (inlet temperature, spray-flow air, feed flow rate and drying air flow rate) on spray-dried nanocapsules when using silica as drying auxiliary agent. The interactions among the formulation parameters and process variables were also studied. Responses analyzed for computing these effects and interactions were outlet temperature, moisture content, operation yield, particles size, and particulate density. Additional qualitative responses (particles morphology, powder behavior) were also considered. Nanocapsules and silica concentrations were the main factors influencing the yield, particulate density and particle size. In addition, they were concerned for the only significant interactions occurring among two different variables. None of the studied variables had major effect on the moisture content while the interaction between nanocapsules and silica in the feed was of first interest and determinant for both the qualitative and quantitative responses. The particles morphology depended on the feed formulation but was unaffected by the process conditions. This study demonstrated that drying nanocapsules using silica as auxiliary agent by spray drying process enables the obtaining of dried micronic particle size. The optimization of the process and the formulation variables resulted in a considerable improvement of product yield while minimizing the moisture content.

Structure and spectra of photochemically obtained nanosized silver particles in presence of modified porous silica

Mesoporous silica powders and films modified with organic sensitizer benzophenone were used as photocatalysts in the reaction of silver ion reduction by isopropyl alcohol under UV‐irradiation with λ = 253.7 nm and 365 nm in presence of colloidal silica as stabilizer. Morphological changes of silver colloids during irradiation were studied using transmission electron microscopy, and correlated to the absorption spectra.

Stream-Subsurface Exchange of Zinc in the Presence of Silica and Kaolinite Colloids

The mobility of sorbing contaminants in surface waters often depends strongly on associations with sediments, including both fine suspended particles and stationary bed sediments. Hydrodynamic flow coupling causes an exchange of dissolved and suspended substances between streams and underlying pore waters (hyporheic exchange). As a result, the fate of many pollutants is expected to be greatly influenced bythe flux of colloids and contaminants across the stream-subsurface interface and the interactions of both types of substances with the bed sediments. Herein, we present experimental results on the stream-subsurface exchange of zinc in the presence of colloidal silica and kaolinite in a laboratory flume. We also apply a process-based theoretical model to predict the coupled transport of colloids and reactive solutes. Model input parameters were obtained using independent batch and column experiments. Zinc immobilization in the bed was found to be significantly greater in the presence of kaolinite than in the presence of colloidal silica. Model predictions indicated that there were two distinct reasons for the greater zinc immobilization in the presence of kaolinite: zinc sorbed more strongly to kaolinite than to silica, and kaolinite particles also deposited more readily in the streambed than did silica colloids. Model simulations were found to be highly dependent on the colloid size distribution. When the colloids had a bimodal distribution, colloidal-phase contaminant transport occurred primarily on the finer fraction, but bulk colloid deposition was dominated by removal of the coarser fraction.

04/00618 Zinc ferrite and related sorbents for hot gas desulfurization process: Ishimori, M. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 413–414

In order to realize the highly effective coal gasification power plants, development of hot-gas cleanup system, especially highly efficient desulfurization technology for hot coal gas is required. We have studied zinc ferrite and related compounds as sorbents for hot reductive gas produced by an entrained-flow gasifier, with consideration of the results of desulfurization operations at Nakoso pilot plant. The characteristics of zinc ferrite and related systems were investigated in terms of sorbents for hot-gas desulfurization process using simple reductive gas involving reductive sulfur substance represented by H2S, as described hereafter. Experimental Sorbents. Zinc ferrite and related sorbents were prepared as follows. A mixed solution of zinc nitrate (1.5 mol/l, 50 ml) and iron nitrate (III) (1.5 mol/l, 100 ml) was stirred in a flask in the presence of colloidal silica. Then ammonia aqueous solution was added to this solution. The precipitates obtained from the solution (pH 7-8) were washed with water after filtration, dried at 120 °C and calcined at 800°C for 5h. ZnFe2O4-SiO2 sorbent thus obtained was confirmed by XRD analysis. ZnFe2O4-SiO2-ZrO2 or ZnFe2O4-SiO2-TiO2 sorbent was prepared by mixing ZnFe2O4-SiO2 sorbent with ZrO2 or with TiO2 (anatase), and calcined at 500 °C for 1h. The composition of the sorbents was determined by the atomic ratio of component oxides using XRF (X-ray fluorescence system) and ICP (Inductively coupled plasma) methods. Desulfurization. Sorbent performance test for desulfurizationregeneration (cycle of sulfidation and oxidation of sorbent) was carried out in a down flow fixed-bed reactor made of quartz under atmospheric pressure. The reductive gas for H2S absorption test is composed of 20% of H2, 1000 ppmv of H2S, and N2 (balance). The sorbent such as ZnFe2O4-SiO2-ZrO2 (or TiO2) system was prepared by composition of 200 mg of ZnFe2O4-SiO2 sorbent and 400 mg of ZrO2 (or TiO2). Analyses of the inlet gas and outlet gas from the reactor were carried out by gas chromatography using a thermal conductivity detector (TCD) and a flame photometric detector (FPD). The total gas flow rate was 100 ml/min (20°C, standard) by using mass flow controllers. Concentration of H2S at the outlet of the

In Situ Polymerized Polyaniline Films. 2. Dispersion Polymerization of Aniline in the Presence of Colloidal Silica,

Composite polyaniline−silica films produced on glass surfaces during the dispersion polymerization of aniline in the presence of colloidal silica were investigated. The film morphology and composition were characterized by FTIR, UV−vis, and X-ray photoelectron spectroscopies. Compared with pure polyaniline films produced under similar conditions, the composite films are thinner and smoother, and their surface is silica rich. The film thickness of both pure and composite films decreased as the polymerization temperature increased from 0 to 50 °C. To determine the particle size of polyaniline-silica dispersion particles, which are formed at the same time as the films, dynamic light scattering was used. The correlation between the particle size and film thickness is discussed. The electrical conductivity of composite polyaniline films was only a little affected by the presence of silica.

Polyelectrolyte-Induced Aggregation of Microcrystalline Cellulose: Reversibility and Shear Effects

The polyelectrolyte-induced aggregation of microcrystalline cellulose (MCC) was studied by focused beam reflectance measurement (FBRM) to determine the reversibility of MCC aggregation under high-shear conditions. A correlation was established between the mean chord length output of FBRM probing a high-shear zone with the mean particle size (laser diffraction) of an aliquot extracted from the low-shear bulk mixing zone. Flocs formed by addition of a cationic polyelectrolyte were ruptured by shear forces of mixing and did not reaggregate at low mixing intensities. Flocs formed by addition of both polyelectrolyte and colloidal silica sols were found to reaggregate at low shear quite reversibly following high-shear degradation. The Kolmolgoroff microscale, η, was determined using a three-compartment mixing model for the FBRM experiments, and the minimum aggregate adhesion forces were calculated to be ∼3 nN under the experimental mixing conditions. Shear-dependent FBRM studies are also used to estimate the radial dependence of particle adhesion forces within an aggregate. AFM-based surface force measurements between model anionic surfaces (mica and glass beads) showed more reversible adhesion forces in the presence of colloidal silica than with cationic polyelectrolyte only. A descriptive model of the interfaces giving rise to the observed MCC aggregation and adhesion behavior is proposed.

Activity losses among T4 lysozyme charge variants after adsorption to colloidal silica

Enzyme structure and function depend to some extent on enzyme net charge and charge location. Altering the charge of even a single residue may affect the interaction between enzyme and substrate such that all catalytic activity is lost. In this study we investigated the effect of net charge and charge location on the enzymatic activity of synthetic mutants of bacteriophage T4 lysozyme in the presence of colloidal silica. Enzymatic activity decreased upon adsorption, and these changes were variant-specific. Results were interpreted with reference to differences in adsorbed enzyme structure and orientation, and electrostatic effects. By exploring the effects of enzyme charge on adsorption, it may be possible to gain a better understanding of how enzyme structure influences adsorption and function at an interface. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 373–376, 1999.

Activity losses among T4 lysozyme charge variants after adsorption to colloidal silica

Enzyme structure and function depend to some extent on enzyme net charge and charge location. Altering the charge of even a single residue may affect the interaction between enzyme and substrate such that all catalytic activity is lost. In this study we investigated the effect of net charge and charge location on the enzymatic activity of synthetic mutants of bacteriophage T4 lysozyme in the presence of colloidal silica. Enzymatic activity decreased upon adsorption, and these changes were variant-specific. Results were interpreted with reference to differences in adsorbed enzyme structure and orientation, and electrostatic effects. By exploring the effects of enzyme charge on adsorption, it may be possible to gain a better understanding of how enzyme structure influences adsorption and function at an interface. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 373–376, 1999.

Surface tension of surfactant solutions in the presence of colloidal silica

Surface tension of surfactant solutions in the presence of colloidal silica

Polyaniline dispersions 7. Dynamic light scattering study of particle formation

When aniline is oxidized in the presence of colloidal silica, composite polyaniline-silica particles of submicrometer size are obtained. Dynamic light scattering was used to monitor the course of dispersion polymerization of aniline and the formation of particles. The increase of a hydrodynamic radius of particles was observed as polyaniline had been produced. Additional increase in particle size after polymerization has also been recorded. The rate of aniline polymerization was found to increase with increasing temperature in the range 0–50 °C. Well-defined particles are formed below 30 °C while above this temperature the colloidal stability of the resulting systems is limited. The activation energy of aniline polymerization was estimated.

Decrease in the Oxidation Potential of the Tris‐2,2′‐bipyridyl Ruthenium(II) Complex Upon Electrostatic Binding to Colloidal Silica as Evidenced on the Basis of the Reaction with the Azidyl Radical

AbstractThe azidyl radical which is otherwise unreactive towards the Ru(bpy)32+ complex reacts with this complex in aqueous solution provided negatively charged colloidal silica particles are present. The increase in reactivity is explained in terms of ion binding, i.e. Ru(bpy)32+ complexes becoming rather firmly attached to the negatively charged particles. The attachment causes a decrease in the redox potential of the system Ru(bpy)33+/Ru(bpy)32+ from E0 = 1.27 V vs. NHE (in the absence of colloidal silica) to E0 = 1.17 V vs. NHE (in the presence of colloidal silica). This value was obtained on the basis of E0 = 1.35 V vs. NHE for the system N3/N3−.