Amino acid-type photo-cleavable surfactants: Controlled dispersion stability of silica particles and release of active ingredients

We synthesized amino acid-type photo-cleavable surfactants composed of coumarin and glycine precursors and studied the photo-switchable interfacial properties, release of active ingredients, and colloidal stability of silica particles. Photo-cleavage of the surfactants reduced their interfacial activities at the squalane/water interface. Silica particles bearing aminoethylene groups on the surface were well dispersed in an aqueous solution of the photo-cleavable anionic surfactant. The surfactants form a bilayer on the silica particles by ion complexation of the amine and carboxylic groups, and the negative charge originating from the surfactant results in electrostatic repulsion, which contributes to the dispersion stability. Ultraviolet light irradiation caused flocculation of the silica particles and the release of the coumarin derivative and glycine into the medium through photo-induced isomerization and cyclization. The new photo-cleavable surfactant systems represented controlled multiple interfacial and colloidal properties upon photoirradiation.