Optical properties of organic-dye-doped spherical particles of polyorganosiloxane derived from methyltrimethoxysilane using a reaction field of W/O emulsion

Abstract

Polyorganosiloxane spherical particles were synthesized by a sol-gel method from methyltrimethoxysilane (MTMS) using a reaction field of W/O emulsion consisting of sorbitantrioleate (SPAN85), n-octane, and aqueous solutions of basic, acid, and oil-soluble organic dyes. The investigation focused on the types of dyes suitable for incorporation into the spherical particles by using this method. The morphology of the particles was observed with scanning electron microscopy (SEM). Fluorescence and ultraviolet-visible (UV-vis) reflectance spectra of dye-doped spherical particles were measured. Basic dyes [Rhodamine B (RB), Rhodamine 6G (R6G), Crystal Violet (CV), Malachite Green (MG), and Thioflavin T (TT)] were doped into the spherical particles. Spherical particles obtained from aqueous solutions of RB, R6G, and CV were colored deeply. However, the MG- and TT-doped particles were scarcely colored. The reason for this color difference was discussed based on the comparison of UV-vis reflectance spectra of dye-doped spherical particles with absorption spectra of starting solutions of the dyes. It is found that the dye that tends to form dimers in aqueous solution was doped more easily than the dyes that tend to form monomers only. On the other hand, spherical particles obtained from acid dyes [Fluorescein Sodium Salt (FSS), Orange G (OG), Naphthol Green B (NGB), and Erythrosin B (EB)] and oil-soluble dye [Fluorescein (FLU)] were all white, confirming that these dyes were not doped in the particles. The reason was discussed in terms of the nature of the dyes and the formation mechanism of the spherical particles.