Preparation of Nanosize Silica in Reverse Micelles:  Ethanol Produced during TEOS Hydrolysis Affects the Microemulsion Structure

Abstract

Microemulsions have been widely used as microreactors for the synthesis of nanoparticles and mesoporous materials. The correlation between the microstructure of a microemulsion and the features of the obtained materials is the most intriguing problem. On this point, many investigations have their ground on the structure of the precursor microemulsion, i.e., the system before the reaction takes place. Nevertheless, any reactions usually involve the formation of byproducts (aside from the nanoparticles). Several of these byproducts (e.g., ions, amphiphilic molecules) could modify the microemulsion structure during the course of the reaction. Here we examine the hydrolysis of tetraethoxysilane (TEOS) in the water-in-oil microemulsion hexadecyl-trimethylammonium bromide (CTAB)/pentanol/hexane/water. Conductivity and NMR measurements performed during the course of the reaction, in combination with dynamic light scattering and pulsed field gradient spin-echo NMR investigation performed on the microemulsion upon the addition of ethanol, indicate that a byproduct (ethanol) modifies the microreactor structure. The ethanol produced by the TEOS hydrolysis drives the microemulsion structure from small disconnected reverse micelles toward large connected aggregates until (for high enough ethanol loading) the system phase separates into two coexisting liquid phases (a dense interconnected network and a dilute reverse micellar phase).

Removal of chromate from water by a new CTAB–silica gelatin composite

“…The silica gelatin composite were prepared starting from the organogels [28]. To define the amount of TEOS we use as parameter the molar ratio water/TEOS (r • ).…”

Formation process of core‐shell microparticles by solute migration during drying of homogenous composite droplets

“…The silica sol is obtained by acid hydrolysis of TEOS, which yields 4 mol ethanol with the generation of 1 mol silica. 39 When RS is mixed with silica sol, the nanoparticles are partially dissolved in ethanol, which results in the partial conversion of the nanoparticles into mixed particulate/fibrous form. It has been reported that Eudragit ® RS tends to form fibrous aggregates in organic solvent.…”

The polymeric nanofilm of triazinedithiolsilane fabricated by self-assembled technique on copper surface. Part 1: Design route and corrosion resistance

“…As a result, the hydrolysis degree of TESPA must be basically determined. The simple approach is to monitor the corresponding conductivity (Ä) of TESPA ethanol/distilled water solution, which was typically used for some silanes [23,24]. This method can be applied to detect the hydrolysis and condensation degrees of TESPA hereon, because TESPA has the similar functional groups as the already studied silanes.…”