Colloidal electrostatic interactions between TiO2 particles modified by thin salt solution layers

We fabricated TiO2 nanoparticles modified by a thin salt solution layer. The suspensions, formed by the nanoparticles in silicone oil, serve as model systems for exploring very general theories about interactions between colloidal particles with arbitrary ions confined on surfaces in the presence of an applied electric field. The system showed a static-yield-stress peak, not found before. The peak can be manipulated by tuning the amount of cations and anions confined in the salt solution layer. Excellent agreement between our experiment and theory reveals the mechanism concerning the competition between ions' polarized trapped state and conductively transmitted state. This work makes it possible to manipulate colloidal interactions by confining exogenous ions appropriately, and it is expected to have applications in colloidal science, materials engineering, and biotechnology.