Aqueous Colloidal Silica Solution Research Articles

Synthesis of polymeric particles with insect repellent for potential application on textile substrates

This paper presents a process for producing particles loaded with the insect repellent ethyl butylacetylaminopropionate (IR3535®). The encapsulated particles were prepared via emulsification using monomers—2-hydroxyethyl methacrylate, methyl methacrylate, and sodium styrene sulfonate—and sodium persulfate—the initiator of the reaction—in an aqueous colloidal silica solution. The emulsion polymerization was carried out at 75 °C for 240 min without surfactants. The encapsulated materials were characterized by dynamic light scattering, electrophoretic mobility, scanning electron microscopy, Raman spectroscopy, and thermogravimetry. The encapsulated particles were in the submicrometric scale with an average diameter of 879 nm, moderate polydispersity index of approximately 0.5, and negative zeta potential. The encapsulation of 12.2% IR3535® was confirmed by high-performance liquid chromatography, demonstrating the efficacy of the encapsulated active material. The emulsion polymerization processes produced insect-repellent-carrying submicroparticles, thereby presenting a promising system for protection against mosquito bites with possible application to textiles.

DEPENDENCE OF TENSILE WET STRENGTH FROM REGENERATION TIME AND GRAIN SIZE OF THE MATRIX CERAMIC MOULDS

Production technology of nwestment casting involves transmitting the elements of shape, dimensions and properties by filling in the appropriate liquid metal ceramic forms reproduced by a model made of wax removed by melting it. The manufacturing process of inwestment casting in the lost wax technology consists of a number of technological operations: preparing of wax models and their assembling in the model units, the preparation of ceramic mixture, successive layers of debris, wax melting in an autoclave, drying the samples at 100 °C, heating the samples at temperatures ranging from 400 to 700 °C. So far, the technology was based on the use of ceramic mixture, which the bond was hydrolysed ethyl silicate. Currently, due to environmental protection and improvement of working conditions, more and more binders with alcohol is replaced with an aqueous solution of colloidal silica. In the study, to create the individual layers a ceramic form, used regenerated ceramic mixture derived from foundry and green ingredients. The regeneration time was respectively 5 and 15 minutes. Used ceramic moulds after mechanical reclamation was given to sieve analysis to determine the grain size (di). Grain sizes 0.2, 0.4 and 0.63 mm were used for the coating of ceramic moulds. The paper presents results of research aimed at the determination of the relationship between tensile wet strength and grain size of ceramic mould: Rm = f[dL). Tests were conducted on cylindrical samples, which deposited the layers of reclaimed ceramic material.

Absorption of carbon dioxide in aqueous colloidal silica solution with NaOH

The absorption rate (R A ) of carbon dioxide was measured into an aqueous nanometer-sized colloidal silica solution of 0–31 wt% and NaOH of 0–2 kmol/m3 in a flat-stirred vessel for various sizes and speeds of 25 °C and 101.3 N/m2 to obtain the volumetric liquid-side mass transfer coefficient (k L a L ) of CO2. The film theory accompanied by chemical reaction between CO2 and NaOH was used to estimate the theoretical value of absorption rate of CO2. The empirical correlation formula containing the relationship between k L a L and rheological property of the aqueous colloidal silica solution was presented. The value of R A in the aqueous colloidal silica solution was decreased by the reduction of k L a L due to elasticity of the solution.

EFFECT OF GRAIN SIZE OF THE RECLAIMED MATRIX CERAMIC MOULDS USED IN THE LOST WAX TECHNOLOGY ON THE STRENGTH AT HIGH TEMPERATURE

Production technology of investment casting involves transmitting the elements of shape, dimensions and properties by filling in the appropriate liquid metal ceramic forms reproduccd by a model made of wax removed by melting it. The manufacturing process of investment casting in the lost wax technology consists of a number of technological operations: preparing of wax models and their assembling in the model units, the preparation of ceramic mixture, successive layers of debris, wax melting in an autoclave, drying the samples at 100 °C, heating the samples at temperatures ranging from 400 to 700 °C. So far, the technology was based on the use of ceramic mixture, which the bond was hydrolysed ethyl silicate. Currently, due to environmental protection and improvement of working conditions, more and more binders with alcohol is replaced with an aqueous solution of colloidal silica. In the study, as the basic of individual layers a ceramic form, used regenerated ceramic mixture derived from foundry and green ingredients. Used ceramic moulds after mechanical reclamation was given to sieve analysis to determine the grain size (dL). Grain sizes 0.2, 0.4 and 0.63 mm were used for the coating of ceramic moulds. The paper presents results of research aimed at the determination of the relationship between tensile wet strength and grain size of ceramic mould: Rm =f(dL). Tests were conducted on cylindrical samples, which deposited a layer of reclaimed ceramic material.

Absorption of carbon dioxide into aqueous colloidal silica solution with different sizes of silica particles containing monoethanolamine

Carbon dioxide was absorbed into an aqueous nanometer-sized colloidal silica solution in a flat-stirred vessel at 25 °C and 101.3 kPa to measure the absorption rate of CO2. The concentrations of silica were in the range of 0–31 wt% and the sizes were 7, 60, and 111 nm. The solution contained monoethanolamine (MEA) of 0–2.0 kmol/m3. The volumetric liquid-side mass transfer coefficient (k L a) of CO2 was correlated with the empirical formula representing the rheological property of silica solution. The use of the aqueous colloidal silica solution resulted in a reduction of the absorption rate of CO2 compared with Newtonian liquid based on the same viscosity of the solution. The chemical absorption rate of CO2 was estimated by film theory using k L a and physicochemical properties of CO2 and MEA.

Mass transfer of carbon dioxide in aqueous colloidal silica solution containing N-methyldiethanolamine

The absorption rate (RA) of carbon dioxide was measured into an aqueous nanometer sized colloidal silica solution of 0–31 wt% and N-methyldiethanolamine of 0–2 kmol/m3 in a flat-stirred vessel for the various sizes and speeds of at 25 °C and 0.101 MPa to obtain the volumetric liquid-side mass transfer coefficient (kLa) of CO2. The film theory accompanied by chemical reaction between CO2 and N-methyldiethanolamine was used to estimate the theoretical value of absorption rate of CO2. An empirical correlation formula containing the relationship between kLa and rheological property of the aqueous colloidal silica solution was presented. The value of RA in the aqueous colloidal silica solution was decreased by the reduction of kLa due to elasticity of the solution.

Absorption of carbon dioxide into aqueous colloidal silica solution with diisopropanolamine

Carbon dioxide was absorbed into the aqueous nanometer-sized colloidal silica solution of 0–31 wt% and diisopropanolamine of 0–2 kmol/m 3 in a flat-stirred vessel with the impeller of various sizes and speeds at 25 °C and 0.101 MPa to measure the absorption rate of CO 2. The volumetric liquid-side mass transfer coefficient ( k L a) of CO 2 was used to obtain the empirical correlation formula containing the rheological behavior of the aqueous colloidal silica solution. Reduction of the measured k L a was explained by the viscoelastic properties of the aqueous colloidal silica solution. The theoretical value of the absorption rate of CO 2 was estimated from the model based on the film theory accompanied by chemical reaction and compared with the measured value.

Chemical Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution with Triethanolamine

Carbon dioxide was absorbed into an aqueous nanometer sized colloidal silica solution of 0–31 wt% and triethanolamine of 0–2 kmol/m3 in a flat-stirred vessel with an impeller size of 0.05 m and speed of 50 rpm at 25°C and 101.3 kPa to measure the absorption rate of CO2. The measured rate of CO2 absorption was compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The volumetric liquid-side mass transfer coefficient (kLaL) of CO2 decreased with increasing silica concentration and was expressed as an empirical correlation formula presenting the relationship between kLaL and the rheological behavior of the aqueous colloidal silica solution. Reduction of the measured kLaL was explained by the viscoelastic properties of the aqueous colloidal silica solution.

Silica/Perfluoropolymer Nanocomposites Fabricated by Direct Melt-Compounding: A Novel Method without Surface Modification on Nano-Silica

A novel method for the fabrication of silica/perfluoropolymer nanocomposites was investigated, whereby nano-sized silica particles without surface modification were dispersed uniformly through mechanical breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a polymer melt during direct melt-compounding. The method consists of two stages. The first stage involves preparation of the loose silica agglomerate, and the second stage involves melt-compounding of a completely hydrophobic perfluoropolymer, poly(tetrafluoroethyleneco-perfluoropropylvinylether), with the loose silica agglomerates prepared in the first stage. In the first stage, the packing structure and the fracture strength of the silica agglomerate were controlled by destabilizing an aqueous colloidal silica solution with a mean primary diameter of 190 nm via pH control and salt addition. In the next stage, the silica/perfluoropolymer nanocomposite was fabricated by breaking down the prepared loose silica agglomerates with low fracture strength by means of a shear force inside the polymer melt during melt-compounding.

Organic/inorganic nanocomposites prepared by mechanical smashing of agglomerated silica ultrafine particles in molten thermoplastic resin

AbstractA new approach for the preparation of organic/inorganic nanocomposites was investigated in which nano‐sized silica particles without surface modification were dispersed by the mechanical smashing of strength‐controlled porous silica agglomerates in molten resin during direct melt‐compounding. The method consists of two stages. The first stage involves preparation of the strength‐controlled agglomerated silica nanoparticles with pore structure, and the second stage involves melt‐compounding of a thermoplastic resin with the silica agglomerates prepared in the first stage. In the first stage, on the basis of the theory of stability of an aqueous colloidal silica solution, the pore structure and the fracture strength of the silica agglomerate could be controlled by pH‐control and electrolyte ion‐addition to the colloidal solutions of silica nanoparticles. In the next stage, primary silica nanoparticles could be dispersed in some matrix resins such as a poly(ethylene‐ran‐vinyl alcohol) and polystyrene uniformly by the proposed mechanical approach by the use of the high shear stress acting on porous silica agglomerates inside these melt‐compounded resins. Copyright © 2006 John Wiley & Sons, Ltd.

Chemical Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution with Diethanolamine

The chemical absorption rate (RA) of CO2 was measured into the aqueous nanometer sized colloidal silica solution of 0–31 wt% and diethanoleamine of 0–2 kmol/m3 in the flat‐stirred vessel with the impeller size of 0.034 m and its agitation speed of 50 rev/min at 25°C and 0.101 MPa, and compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The value of the volumetric liquid‐side mass transfer coefficient (kLa) of CO2, which was used to estimate the value of RA, was obtained by the empirical correlation formula presenting the relationship between kLa and the rheological behavior of the aqueous colloidal silica solution. The value of RA in the aqueous colloidal silica solution was decreased by the reduction of kLa due to the elasticity of the solution.

Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution

On the basis of experimental data for carbon dioxide absorption into aqueous nanometer sized colloidal silica solution as a non‐Newtonian fluid, a dimensionless correlation for volumetric liquid‐side mass transfer coefficient (kLa) of CO2 in the flat‐stirred vessel was proposed. In addition to ordinary liquid properties and operating parameters such as impeller size and speed in the vessel, Deborah number, which is defined as the product of the characteristic material times of the liquid and agitation speed in the flat‐stirred vessel and represents the viscoelastic behavior of non‐Newtonian fluid, was used to present unified expressions for kLa in Newtonian as well as non‐Newtonian liquid. The values of kLa in the aqueous colloidal silica solution were reduced due to elasticity of the solution.

Uranyl photophysics on colloidal silica: an alternative luminescence-enhancing medium for uranyl assay

The luminescent behaviour of uranyl (UO22+) in aqueous colloidal silica solution is illustrated and its biexponential decay with time investigated. The two components have lifetimes of 240 and 55 µs and after about 1.5 h the decay becomes monoexponential with a lifetime of 240 µs and luminescence quantum yield approaching 25%. The absorption and emission spectra are red shifted and greatly enhanced compared with those in dilute aqueous perchloric acid solution. The suitability of aqueous colloidal silica as a dispersed medium for enhancing luminescence to detectable levels for concentration measurements is also shown, with uranyl concentrations down to 10 nmol dm–3(0.2 ppb) being routinely measurable. The luminescence of uranyl on dried silica gel is found to be almost identical with that of uranyl in aqueous colloidal silica, illustrating that the uranyl is extremely closely associated with the silica surface and thereby sheltered from quenching by water molecules. This colloidal enhancing medium has advantages over traditional methods used in that a longer lifetime is achieved, diffusional quenching by anions is considerably reduced and the uranyl can be easily extracted from bulk solution.