Study of the Stoeber reaction. 1. Properties of colloidal silica spheres prepared via alkoxide hydrolysis

Synthesis of Microporous Silica Spheres

“…At the end of the precipitation, the concentration of silicic species becomes below the critical supersaturation and nucleation stops. Under this condition, the silica particle may grow by monomer addition to the particle surface, as was observed by several authors for systems operating at low TEOS concentration (9)(10)(11).…”

“…Considering the rate of condensation faster than hydrolysis, it was found that TEOS hydrolysis was the rate-limiting step. Further development of this theory has convinced several authors to consider a monomer addition model where nucleation occurs whenever two hydrolyzed silicates condense (9)(10)(11). Diffusivities of reacting species were measured by Bogush and Zukoski in a kinetic study of the uniform silica particle precipitation (8).…”

Shell particles, trials, tribulations and triumphs

“…The average size of the particles used to pack HPLC columns was initially in the 100 m range [19,20]. Later, this average size decreased progressively to 40-50 [4,21], then to 20, 10 [20], and 5 m, a range that was already reached in the early 1980s and remained nearly unchanged until the turn of this century, in spite of the availability of 3 m and even smaller 1 m particles [22]. The only major change that took place in the 1980s and 1990s was the development of spherical particles that eventually came to dominate entirely the market of packing materials.…”

“…Then, under the combined pressures of the requirements by the pharmaceutical and fine chemicals industries for accelerated analytical throughputs and the threats of the monolithic columns that were commercialized in 2000 with great expectations, the manufacturers of packing materials capitalized on their experience in the production and packing of regular, spherical, reproducible 5 m particles [23][24][25][26][27][28] and rapidly began to commercialize columns packed with 3, then 2, and now with the sub-2 m particles, which have average sizes between 1.5 and 1.7 m. Finer particles, with average size of 1 m are already available for nearly ten years but with limited commercial success because these are solid, nonporous particles [22]. Then, a few years ago, the concept of shell particles was suddenly revived to an amazing success [29][30][31].…”

Charge reversal of moisturous porous silica colloids by take-up of protons

“…5d the porosity is varied, this can be realized experimentally for example by slowing down the growth rate during the Stö-ber synthesis process [25]. Within the present model we assume that all the pores are accessible for ions in the surrounding oil phase, at least in a layer within tens of nanometers from the surface, as Fig.…”