A critical reappraisal of recent communications on the hydrodynamic characterization of silica (aerosil) hydrosols

Different results from recent communications on the hydrodynamic characterization of ultrasonicated silica (®Aerosil) hydrosols led to a critical reappraisal of the data.It can be concluded that the degree of dispersion achievable in pyrogenic (Aerosil) hydrosols by ultrasonication is highly sensitive to the detailed parameters of the dispersion process. Characterization in terms ofabsolute numbers of a limiting particle morphology, corresponding to minima of aggregate size, porosity and number of primary particles in the aggregate is not possible.The most straightforward approach for hydrodynamic characterization seems to be a combination of sedimentation and diffusion data.Other approaches using a combination of sedimentation and viscosity data underestimate the particle dimensions. Moreover, they are quite arbitrary since the final result depends upon the proper choice between several equations for fitting the viscosity concentration dependence; the most rigorous approach seems to be an extended Einstein equation which has recently been adapted to particle aggregates.     

The study of the emulsification efficiency of Aerosil and HPMCAS type and their ratio to stabilize emulsions of zedoary turmeric oil

The solid particles or polymers were often solely used to stabilizing emulsions, as an interesting alternative to classical used emulsifiers. However, a united use of them and the relation between them at stabilizing emulsions were little reported. Our previous study showed that the preparation of microspheres containing zedoary turmeric oil (ZTO, as an oily drug), Aerosil200 particles and hydroxypropyl methylcellulose acetate succinate (HPMCAS). ZTO emulsions were produced when the microspheres were immersed into aqueous media and disaggregated under gentle agitation, and were stabilized by Aerosil200 particles and HPMCAS. Nevertheless, more work needs to be carried out to explain the factor affecting emulsification efficiency of microspheres, which will facilitate the design of the microsphere formulation. Thus, in this study, we dealt with a system consisting of Aerosil, HPMCAS, ZTO and water. To predict the best ratio of Aerosil/polymer and thus obtain the best satisfying ZTO emulsions, the bonding studies were carried out with Aerosil and HPMCAS. A series of emulsions was prepared and the stability and droplet size of resultant emulsions were investigated. The results indicated two kinds of HPMCAS (HPMCAS-LG and -HG) showed the different affinity for Aerosil200, which resulted in the unlike capability to stabilize emulsions when at the same Aerosil/polymer ratio. The stability and droplet size of emulsions increased on increasing the ratio Aerosil to polymer, and the best ratio was predictable from the Langumuir-fit of the adsorption isotherms. Appropriate hydrophilicity and hydrophobicity with Aerosil particles were very important to stabilizing the ZTO emulsions.     

A study of the interaction of diethylzinc with the Aerosil surface

The interaction of diethylzinc with Aerosil has been examined by IR spectroscopy and mass spectrometry. The reaction involves both free hydroxyl groups and siloxane groups of the surface resulting in the formation of Si-O-Zn-Et and Si-Et fragments. At temperatures above 300 °C, these structures undergo decomposition with the recovery of Si-OH groups on the Aerosil surface and liberation of metallic zinc.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1666–1668, September, 1994.The authors are grateful to M. B. Molotovshchikova for continuous help in performing the experiment.     

Effect of pH and Salt on Rheological Properties of Aerosil Suspensions

Ionic strength and pH will influence the zeta potential of suspended particles, and consequently particle interactions and rheological properties as well. In this study the rheological properties and aggregation behaviour of Aerosil particles dispersed in aqueous solutions with various pH and salt concentration were studied. The potential energy was estimated by the DLVO theory and short range hydration forces and compared to the experimentally determined zeta potential. The strongest attraction between particles occurs at the isoelectric point (pH 4) and resulted in large aggregates, which gave relatively higher values of viscosity, yield stress, moduli, and shear thinning effects. The relative viscosity as a function of volume fraction was fitted to the Krieger and Dougherty model for all the suspensions. Oscillation measurements showed that the suspensions display elastic behaviour at low pH and viscous behavior at high pH. Furthermore, suspensions with high salt content had higher storage moduli. A power law dependency of storage moduli with volume fraction could be used to indicate the interaction strength between particles.     

Determination of the concentration of hydroxyl groups on aerosil surfaces

The concentration of the hydroxyl groups on Aerosil surfaces was estimated by chemical analysis and IR spectroscopy. The temperature ranges for thermal stability of the OH groups and for their reactivity in surface chemical reactions were established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1757–1760, October, 1997.     

Dispersion of Nanoparticle Clusters by Ball Milling

The full and complete dispersion of nanoparticles is critical to enabling industry to formulate products which exploit the properties of such materials and hence realize the full economic value of such products.

Ball milling is conventionally used for the comminution of particle slurries and, of the various wet milling techniques, is the most effective in producing fine particle sizes. Here we consider the use of a ball mill (also referred to as a stirred media mill) for the dispersion of a slurry of nanoparticle aggregates and compare its performance to a typical rotor‐stator device commonly used by industry. The slurry is an aqueous dispersion of Aerosil 200 V that has a primary particle size of about 12 nm and comes as a dry powder. On dispersion in water it forms large aggregates which are difficult to fully disperse. Aerosil is readily available in quantity and is used in a number of industrially relevant applications and so is an ideal test material for such trials.

A lab scale Fryma Co‐Ball mill (0.5 L volume) is used and the effects of bead fill (40–70%), flow rate (0.1–1 kg/min) and rotor speed (7.5–18 m/s) are investigated. Specific energy is the most effective ways to correlate performance to particle size suggesting that residence time (i.e., flow rate) is the most important process parameter. Lower rotor speeds are also shown to be more energy efficient. The correlations show that the ball mill provides a significant improvement in dispersion (d[3,2]=0.61 µm) over the conventional rotor–stator device.     

Characterization of Surface Modified Silica Nanoparticles by 29Si Solid State NMR Spectroscopy

 Various aerosils surface modified with silane reagents were prepared and investigated by ²⁹Si solid state NMR spectroscopy. The mode of bonding onto the silanol surface (mono- or divalent) can be specified by comparison with chemical shifts from solution. A detailed analysis also leads to the detection of products formed via hydrosilylation reactions. A rough quantification of the surface loading can be obtained by a signal deconvolution process of the silanol resonances on the Aerosil surface.     

Cyclopropane ring opening in the reaction of methylenecyclopropane with silyl radicals stabilized on an activated Aerosil surface

Alkyl type radicals stable at room temperature and incorporating a double bond not conjugated with the free valence, ≡Si−C(=CH₂)−CH₂−CH₂, are formed in the reaction of methylenecyclopropane with silyl radicals (≡SiO)₃Si on an activated Aerosil surface. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1065–1066, May, 1997.     

A novel composite microsphere as a highly efficient absorbent for oils and organic solvents

A novel composite oil‐absorbent microsphere poly(stearyl methacrylate‐co‐butyl acrylate) (PSB)‐SiO₂ was prepared by introducing hydrophobic nano‐silica Aerosil R812 into the suspension polymerization system of stearyl methacrylate and butyl acrylate and was characterized by Fourier transform infrared and scanning electron microscopy energy‐dispersive spectrometer. PSB‐SiO₂ has a loose network structure and exhibits remarkably fast oil absorption speed in relatively high saturated oil absorbency. Besides, PSB‐SiO₂ has good oil retention and reusability. Moreover, the saturated oil absorbencies of PSB‐SiO₂ toward toluene, gasoline, and diesel over water are roughly equivalent to that in pure oil. Owing to its excellent oil absorption performances, PSB‐SiO₂ will find applications in removing oil spills and organic pollutants over water. Copyright © 2016 John Wiley & Sons, Ltd.     

Non-supercritically dried silica–silica composite aerogel and its possible application for confining simulated nuclear wastes

The simpler non-supercritical drying approach has been used for the first time for the preparation of silica–silica composite aerogels (CA) and the efficiency of the process being demonstrated by testing the use of the aerogels for simulated high level nuclear waste confinement. Compositions of 5, 10, 20, 30, 40 and 50 wt% of silica (aerosil® 380) in silica–aerogel were prepared by introducing pyrogenic silica in to silica sol derived by hydrolysis of Tetraethoxy silane (TEOS). The silica–silica composite aerogels (CA) possessed very high surface area and low bulk densities. The effectiveness of the prepared composite aerogels as precursor for high level nuclear waste immobilized glass is also presented. Neodymium nitrate dissolved in isopropanol is used to simulate +3 valent actinides. The stability of neodymium in the glass matrix has been found to be extremely high. Transmission electron microscopy (TEM) has been used to characterise the aerogels as well as neodymium incorporated sintered gels. X-ray diffraction (XRD) studies of the sintered samples reveal the formation of neodymium silicates.