Photocontrol of dispersibility of colloidal silica

Abstract The surface of colloidal silica particles was chemisorbed with spirobenzopyran molecule having a long hydrocarbon chain. The spiropyran silica particles (SP-CS) displayed normal photochromism. When SP-CS were dispersed in carbon tetrachloride, UV irradiation induced flocculation of the particles to bring about markedly enhanced sedimentation. Subsequent visible irradiation recovered the dispersed state again.