(142n) Diffusion Driven Flows in Multi-Ionic Systems

Diffusioosmotic flows occur in gradients of salt concentration, by a much-studied process. The essential physics is that the ions in the salt have different diffusion coefficients, and in order to maintain electroneutrality, a spontaneous electric field arises in the system. This electric field drives a diffusioosmotic flow at charged surfaces, and diffusiophoresis of charged particles. A common approach is to impose an external salt gradient on a system, and then to follow the transport of particles as they move by diffusiophoresis. In this talk, we do not impose salt gradients, but rather, allow the particles themselves to self-generate the gradients in ionic strength. Using mineral particles, such as calcite (CaCO3) or gypsum (CaSO4), we enable flows to be generated and tracer particles to be moved. To better study the process, and delineate it from any convective or density driven flow mechanism, we consider the case where salt gradients generated from divalent salts in the presence of monovalent ions can generate flows in vertical systems of ‘a reservoir and a sink’ system. We study this in the presence of monovalent ionic species (e.g. KCl and NaCl) and generate an experimental and theoretical model showing diffusion driven flows in such cases. We show that the velocity of these tracer particles can be related to essential parameters of the systems, such as the Ksp of the minerals, the diffusion coefficients of the ions resulting from the dissolved mineral, the zeta potentials of the particles and surfaces, and even the change of zeta potentials resulting from the dissolution of minerals. These data, and our interpretations of them, will be presented in this talk.