Surface Area Of Silica Particles Research Articles

Effects of BET Surface Area and Silica Hydrophobicity on Natural Rubber Latex Foam Using the Dunlop Process

To reinforce natural rubber latex foam, fumed silica and precipitated silica are introduced into latex foam prepared using the Dunlop process as fillers. Four types of silica, including Aerosil 200 (hydrophilic fumed silica), Reolosil DM30, Aerosil R972 (hydrophobic fumed silica), and Sipernat 22S (precipitated silica), are investigated. The latex foam with added silica presents better mechanical and physical properties compared with the non-silica foam. The hydrophobic nature of the fumed silica has better dispersion in natural rubber compared to hydrophilic silica. The specific surface area of silica particles (BET) also significantly influences the properties of the latex foam, with larger specific surface areas resulting in better dispersity in the rubber matrix. It was observed that exceeding 2 phr led to difficulties in the foaming process (bulking). Furthermore, higher loading of silica also affected the rubber foam, resulting in an increased shrinkage percentage, hardness, compression set, and crosslink density. The crosslink density increased from 11.0 ± 0.2 mol/cm3 for non-silica rubber to 11.6 ± 0.6 mol/cm3 for Reolosil DM30. Reolosil DM30 also had the highest hardness, with a hardness value of 52.0 ± 2.1 IRHD, compared to 45.0 ± 1.3 IRHD for non-silica foam rubber and 48 ± 2.4 IRHD for hydrophilic fumed silica Aerosil 200. Hydrophobic fumed silica also had the highest ability to return to its original shape, with a recovery percentage of 88.0% ± 3.5% compared to the other fumed silica. Overall, hydrophobic fumed silica had better results than hydrophilic silica in both fumed and precipitated silica.

Towards tunable size of silica particles from rice husk

Amorphous spherical silica particles were produced in a variety of sizes ranging from nanometer to micrometer from rice husk by varying the concentration of white rice husk from 0.7wt.% to 5.6wt.% in sodium hydroxide to form sodium silicate solutions. The effect of increased reaction temperature (65°C) and the addition of water on the size of silica particles was also studied. At low concentrations of white rice husk (0.7wt.% and 1.4wt.%), uni-modal silica particles in nanometer size range were produced while at higher concentrations (2.8wt.% and 5.6wt.%), bi- and tri-modal particles were produced, which were converted to uni- and bi-modal by changing the reaction conditions, i.e. water and temperature, respectively. X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy and atomic absorption spectroscopy were employed for the compositional analysis of white rice husk and sodium silicate solution. Scanning electron microscopy was used to study the morphology and particle size of silica while X-ray diffraction confirmed the amorphous state of silica particles. Surface area of silica particles was analyzed by using Brunauer–Emmett–Teller analysis.

Impact of surface area of silica particles on dissolution rate and oral bioavailability of poorly water soluble drugs: A case study with aceclofenac

This study aims to evaluate the impact of surface area of silica particles on in vitro release of poorly soluble drug aceclofenac and their in vivo performances. Mesoporous silicas of different surface area and porosity were synthesized and characterized. Aceclofenac loaded silicas were prepared by solvent evaporation technique and characterized for surface area, pore size, DSC, FTIR and p-XRD. The dissolution efficiency (DE) of the mesoporous and nonporous silica was ∼2 times more than that of plain drug and marketed tablets in acidic discriminating media. A significant enhancement of 189% and 164% in oral bioavailability (AUC0-8) was observed for optimized aceclofenac loaded mesoporous formulation (MS11/72) and nonporous silica (NP), respectively, when compared to plain aceclofenac in male Wistar rats. However, no correlation could be established between the enhancements in their oral bioavailability and their corresponding surface area. The surface area of MS11/72 was 5 times more (∼1011 m(2)/g) when compared to NP (∼200 m(2)/g) and the enhancement in the oral bioavailability was only 1.15 times. This could be due to the limiting value of effective surface area of the drug available for in vitro dissolution beyond which, any further increase in surface area fails to improve the release rate or its bioavailability.

Effect of immobilized interfacial layer on the maximum filler loading of polystyrene/silica nanocomposites

The effects of filler particle size and volume fraction on the immobilized interfacial layer volume and maximum filler loading of filled polymers are investigated using polystyrene-containing silica nanoparticles. The samples are prepared by solution-mixing method to obtain a better dispersion of silica particles, and dynamic rheometry is used to study viscoelastic behavior of these composites in the melt state. Addition of silica particles increases the glass-transition temperature; this phenomenon is intensified by decreasing the silica particle size. By decrease in size of silica particles, glass transition of filled polymer increases simultaneously with increase of interfacial layer volume fraction, which is related to increase in the total surface area of silica particles. Furthermore, the growth of immobilized interfacial layer volume fraction reduces the maximum filler loading as the filler particle size decreases.

Synthesis of spherical silica particles by sol‐gel method and application

AbstractSpherical silica particles were synthesized using the sol‐gel method by hydrolyzing tetraethyl orthosilicate (TEOS) with an alkali catalyst, and it was investigated how the experimental conditions (the reaction temperature, the concentration and dropping rate of the hydrolysis catalyst solution) affected the size and morphology of silica particles. Furthermore, the silica particles were doped with sodium fluoride to measure their ion release ability. The mean diameters of the silica particles changed according to the reaction temperature and the dropping rate of the hydrolysis catalyst, namely the higher the reaction temperature or the slower the dropping rate the smaller are the mean diameters. The surface area of the silica particles was significantly different depending on the dropping rate of the hydrolysis catalyst, namely the slower the dropping rate the larger the specific surface area. The specific heat capacity and thermal reduction (TG) of the silica particles were significantly different according to the reaction temperature, namely the higher the reaction temperature the lower the specific heat capacity and the TG. It was found that the fluoride‐retaining ability was proportional to the surface area of silica particles. The fluoride ion release was equilibrated on elapsing 5 min. Copyright © 2008 John Wiley & Sons, Ltd.

Synthesis and Characterization of Silica Nanoparticles

Currently there are several models discussed to describe the formation of monodispersed silica particles. Monodisperse colloidal silica was prepared from tetraethoxysilane in mixture of ammonia, water and ethanol. Chemical system reaction permits the controlled growth of silica nanoparticles and subsequent condition of silicic acid in alcoholic solution. The molar ratio of NH4OH, C2H5OH and H2O has a significant effect on particle size and specific surface area of silica particles. The nature of particles was evaluated using X-ray diffraction, energy dispersive spectroscopy (EDS) and BET. The morphology of particles were determined by scanning electron microscopy (SEM) and transmission electron microscopy(TEM).

Fatty acid methyl ester production using lipase-immobilizing silica particles with different particle sizes and different specific surface areas

Twelve kinds of silica particles, with particle sizes of 1.6–700 μm and specific surface areas of 14–620 m 2/g support, were investigated as lipase-immobilizing supports for the production of fatty acid methyl ester (FAME). When the particle size and specific surface area of silica particles became smaller, the maximum enzymatic reaction rate was at a high level. Scanning electron microscopy revealed that the surfaces of lipase-immobilizing silica particles were coated by a lipase layer. At higher lipase loading than 20%, the lipase formed multilayers or wrinkled sheets on the silica surface and some of them peeled off. Lipase activity was proportional to the increase in the enzyme loading on silica particle until 30%, but the FAME formation rate was proportioned to the enzyme loading until 20%, and remained at a maximum level at lipase loading higher than 20%. The lipase-immobilizing silica particle did not lose activity following agitation rate at a 150 rpm for 8 h and 118 d of storage at room temperature. When lipase-immobilizing silica P-707 with at a specific surface area of 300 m 2/g was used, the FAME conversion remained at 80% until the 16–20th cycle, and decreased to 20% after the 33rd cycle. The lipase immobilized on P-707 produced 57 g FAME per gram of lipase. Total FAME production increased with an increase in the specific surface area of silica particles, but it was not influenced by particle size over 40 μm. During the progress of a long-term esterification reaction, the outer layer lipase was first inactivated, and then the inner layer of lipase was inactivated.

Preparation of PEG-grafted silica particles using emulsion method

Low-molecular-weight poly(ethylene glycol) (PEG) was grafted onto the surface of silica particles by a two-step addition process. To prepare PEG-grafted silica particles, PEGME–IPTES monomers were synthesized by the reaction of 3-(triethoxysilyl)propyl isocyanate (IPTES) with poly(ethylene glycol) methyl ether (PEGME) in the presence of dibutyltin dilaurate. To remove PEGME residues, excessive IPTES was added to the solution. The peak for a urethane carbonyl group of PEGME–IPTES was observed at 1722 cm −1 by FT-IR spectroscopy. Through the sequential addition of TEOS and PEGME–IPTES monomers, PEG was introduced onto the surface of silica particles. The introduction of PEG onto the surface was observed by SEM, Brunauer–Emmett–Teller (BET), and FT-IR spectroscopy. When PEG was grafted onto the surface of silica particles, the surface area of silica particles decreased and the average pore diameter increased. The peak for urethane carbonyl group and alkyl group of PEG appeared at 1722 cm −1 and 2920 cm −1.

Effects of Surface Chemistry of Silica Particles on the Mechanical Properties of Silica Filled Styrene–Butadiene Rubber Systems

The effects of surface chemistry of silica particles on the mechanical properties were studied for silica filled styrene–butadiene rubber (SBR) systems. The samples were prepared from different kinds of silicas and of silane coupling agents. The breakdown of the agglomerate formed by silica particles was successfully detected by transmission electron microscopy (TEM) observations when the strain was applied to silica filled vulcanizates. The degree of breakdown of the agglomerate of silica particles by the strain was more prominent in the larger one of which size was controlled by the number of silanol group per unit surface area of silica particles. The amount of entrapped rubber within the agglomerate seemed to be decreased with the decrease in the agglomerate size. Also, the initial agglomerate size and the change of agglomerate by the strain became small by the introduction of silane coupling agent, such as bis(3-triethoxysilylpropyl)tetrasulfane (TESPT). At a given degree of vulcanization, the initial modulus of silica filled vulcanizates was governed by the size of agglomerate formed by silica particles and the amount of entrapped rubber phase. On the other hand, at a larger strain, the tensile strength of the filled vulcanizates increased by the introduction of interfacial combination between silica particles and rubber matrix by TESPT. These results indicate that the stress-strain behavior of filled vulcanizate is affected by the agglomerate of the fillers and the interactions between filler and rubber matrix.

Effects of secondary structure of fillers on the mechanical properties of silica filled rubber systems

A study was carried out on the mechanical properties of silica filled styrene–butadiene rubber systems in relation to the secondary structure formed by silica particles in the systems, which was controlled by a surface chemistry of silica particles and by a strain applied to the samples. The breakdown of the secondary structure was successfully detected by transmission electron microscopy (TEM) observations when the strain was applied to silica filled vulcanizates. The degree of breakdown was more prominent in the larger agglomerates of which the size was controlled by the number of silanol group per unit surface area of silica particles. The existence of the entrapped rubber within the agglomerate was suggested by the TEM image analysis. A part of the entrapped rubber might be released when the filler network was broken by a strain. The initial modulus of the filled rubber systems increased with the increase in the size of agglomerate. At a larger strain, the modulus decreased with the increase in the strain. The decrease was more prominent in the filled rubber, which had larger agglomerates. The reduction of modulus by the strain was closely related to the reduction of entrapped rubber phase within the agglomerates and to the breakdown of secondary structure of silica particles.

The role of ferrocene in flame synthesis of silica

The effect of ferrocene additive on the specific surface area of silica particles synthesized in a diffusion flame reactor was studied. Three different mixing configurations of the reactant gases were investigated. The SiCl 4 mole fraction in the flame was varied from 1.2 × 10 −3 to 4 × 10 −3. Ferrocene concentrations in the flame ranged from 4 × 10 −8 to 6 × 10 −7 mol/L. The ferrocene/SiCl 4 mole ratio was varied from 0.004 to 0.09. Silica particles collected from ferrocene-doped flames had a higher specific surface area compared with particles produced in the absence of ferrocene. The specific surface area was enhanced up to 150% depending on the reactant mixing and the silica and ferrocene loadings in the flame. Ferrocene was more active at intermediate loadings. Furthermore, ferrocene was found to remove the coarse tail of the silica aggregate size distribution.