(179d) Colloidal Particle Halos in Ternary Particle System

Colloidal particle halos are a concept in which small particles are trapped in a shallow energy well close to the surface of larger particles. The object of this work is to experimentally determine if halos of submicron particles around larger, micron-sized particles could be produced by the presence of nanoparticles. Specifically, the nanoparticles should produce attractive depletion forces between the micro- and submicro-particles of sufficient magnitude to create a halo of the submicroparticles.  Colloidal probe atomic force microscopy (CP-AFM) was used to measure the force profile between a single silica microparticle and silica plate in a solution containing both submicroparticles and nanoparticles, also of silica.  The experiments were performed at pH 4.5, such that all surfaces were negatively charged.  The measured force profiles were compared to those obtained by using the solution of submicroparticles only or nanoparticles only, and also with a force-balance model that predicted the equilibrium force profile.