One-pot spontaneous formation of submicron hexane-dispersible silica particles with the aid of amphiphilic reaction solvent

Abstract

Hydrophobic submicron hybrid silica particles were spontaneously formed in the mixture of tetraethylorthosilicate (TEOS) and hexyltrimethoxysilane (HTMS) dissolved in diethylamine, which works as a catalytic Lewis basic amphiphilic reaction solvent. The obtained hybrid silica particles were stably dispersed in non-polar solvent such as hexane in the form of the primary-particle dispersion. The solvent diethylamine functioned not only as the catalyst for the silanol polycondensation but also as a superior dispersant for the primary-particle dispersion of the hydrophobic hybrid silica particles throughout the formation process. After the addition of TEOS, HTMS and water in diethylamine, the particle nucleation was promoted the ultrasonication for 30 s. Then, the uniform-sized submicron hydrophobic hybrid silica particles were spontaneously formed after the dispersion of the nuclear was kept still for 24 h. The surface of the hybrid silica particles became increasingly hydrophobic. This is because of the higher density of the non-polar pendant groups (hexyl groups) in the vicinity of the surface, which results from the lower reactivity of trifunctional HTMS than that of tetrafunctional TEOS. The merits of using diethylamine are summarized as follows; 1) Since diethylamine strongly catalyzes silanol condensation, the particle surface was thoroughly hydrophobized. 2) Since the hydrophobized particle had good affinity with diethylamine, the hybrid silica particles remained stably dispersed in it. Furthermore, even after the hybrid silica particles are air-dried, they are redispersed in hexane in the form of the primary-particle dispersed.