Encapsulation of three different hydrophobic dyes in functionalized silica particles

This paper describes a method to prepare silica particles able to encapsulate 3 different hydrophobic dyes: Disperse Red, Solvent Red and 2-{4-4-(Benzyl-ethyl-amino)-phenylazo]-benzenesulfonyl}-ethanol (HESA). Dye doped silica particles were prepared by the sol–gel process in aqueous medium, with a base catalyst, using various concentrations of a “home made” surfactant (named NP₉-Si). The surfactant is the addition byproduct of –OH groups of polyethylene glycol nonylphenyl ether Tergitol^® NP-9 with -NCO groups from (3-isocyanatopropyl) triethoxysilane and was added to increase both the stabilization of the silica particles and the compatibility of the inorganic network versus the dopant (the aromatic dye). It was shown that there is an optimum range of the amount of surfactant which should be added in the sol–gel reaction system. If a higher amount of surfactant is used, it forms probably micelles which entrap the dye and prevent its encapsulation in the formed silica particles. Because the silica particles are designed to encapsulate systems containing aromatic derivatives (aromatic dyes) we used phenyltriethoxy silane and tetraethylorthosilicate as silica precursors. As coupling agent for the silica network we used a bis (trialkoxysilane) derivative—1,2-bis (triethoxy silyl) ethane.