Aerosil, Herstellung, Eigenschaften und Verhalten in organischen Flüssigkeiten

Amorphous SiO2 surface models: energetics of the dehydroxylation process, strain, ab initio atomistic thermodynamics and IR spectroscopic signatures

Realistic amorphous SiO₂ models of 2.1 × 2.1 nm with silanol densities ranging 1.1–7.2 OH per nm² are obtained by means of ab initio calculations via the dehydroxylation of a fully hydroxylated silica surface.

Industrial applications of nanoparticles

This tutorial review analyses where nanoparticle research has left the laboratory and today contributes to valuable products.

Solid phase adsorption of crystal violet lactone on silica nanoparticles to probe mechanochemical surface modification

The solid phase adsorption of crystal violet lactone (CVL) on five types of Stober silica nanopowders with BET specific surface areas in the range of 50-800 m2/g under dry milling conditions was described for the first time. The hydrogen bonding between surface silanol and the carboxylate of the ring-opened triphenylmethane dye (CVL+) led to the formation of monolayers of CVL+ in a flat-laid configuration. The lambda max of CVL+ in diffusive reflection visible spectra was influenced by the particle size of silica powders, suggesting that the microenvironmental polarity of adsorbed CVL+ is considerably reduced along with the decrease of the particle size. The solid phase adsorption of CVL obeyed Langmuir adsorption isotherms to give a saturated amount of CVL+ for every silica nanoparticle. The surface concentration of CVL+ on nanoparticles at the saturation was estimated to be 0.31 mg/m2 on average, disclosing that about 52% of the surface can be covered by CVL+ under the assumption that the BET-specific surface areas are equivalent to the real surfaces active for the CVL adsorption. The generation of the blue color of CVL provided a convenient means to estimate qualitative and quantitative analysis of the surface coverage with surface-active reagents, which conceal surface silanols. Subsequently, silica nanoparticles were milled with a surface modifier, followed by milling with CVL to observe the intensity of the blue color in order to disclose that the surface coverage with oligo- and polyethylene glycols as well as with nonionic surfactants by dry milling was specifically determined by the number of repeating oxyethylene units. Although the surface-active reagents were easily desorbed in water, the desorption was notably suppressed by milling with CVL, suggesting that the surface-modified particles with the surface-active reagents are covered with ultrathin films of CVL.

Tailor-made nanoparticles via gas-phase synthesis

Gas-phase synthesis is a well-known chemical manufacturing technique for an extensive variety of nanoscale particles. Since the potential of ultrafine and, in particular, nanoscale particles in high-performance applications has been identified, scientific and commercial interest has increased immensely, thus identifying this field as a most important technology of the future. However, nanomaterials can perform their multifunctional tasks only if they are customized in terms of chemical composition, size, and morphology to suit the application at hand. Profound knowledge of the synthesis and precise process control is crucial in meeting the stringent specifications. Although the gas-phase synthesis of ultrafine materials has been known and commercially exploited for decades, existing knowledge is based almost exclusively on empirical know-how. Process simulation is a very suitable tool for expanding the understanding of the synthesis-relevant processes, particle formation mechanisms, and operating parameters. Based on the resulting expertise some special nanoscale gas-phase products of high innovative potential have been developed.

Porous Silica Particles Prepared from Silicon Tetrachloride Using Ultrasonic Spray Method

Silica particles having the median diameter of 1 to 3 µm were prepared from silicon tetrachloride vapor by a reaction with water droplets using the ultrasonic spray method. The particle sizes of silicas were controlled by changing the composition of silicon tetrachloride and water. These silica particles had microporous structures from nitrogen and water adsorption measurements. The microporous and mesoporous particles were prepared from the reaction of water droplets including sodium and potassium carbonates with silicon tetrachloride vapor. Copyright 1999 Academic Press.