COLLOIDAL INTERACTIONS IN WATER 2-BUTOXYETHANOL SOLVENTS/

The behavior of a colloidal silica dispersion in the mixed solvent of H2O or D2O and 2-butoxyethanol (C4E1) is studied as a function of solv ent composition and particle volume fraction. Under certain conditions , the silica particles undergo a phase transition (gas/liquid) that is reversible on dilution or cooling. Small angle neutron scattering mea surements are performed on one-phase samples, and the resulting scatte ring curves are modeled using appropriate forms of the pair interactio n potential. In D2O, the silica particles are highly charged and stabi lized by Coulombic repulsion. As the C4E1 content of the solvent is in creased, Coulomb forces are diminished and the particles behave as har d spheres. At higher C4E1 concentrations, attractive interparticle int eractions become important and the particles behave like sticky hard s pheres. The sticky hard sphere parameters obtained from fits to the sc attering data compare well to those required by theory to match the ob served phase boundary.