(678e) Diffusioosmotic Flow Reversals Due to Ion-Ion Electrostatic Correlations in a Mixture of Electrolytes

Diffusioosmosis is to the deterministic fluid motion induced by a solute concentration gradient. Existing theories of diffusioosmosis have neglected ion-ion electrostatic correlations which are important in multivalent or concentrated electrolytes. Here, we develop a mathematical model to compute the diffusioosmotic mobilities of a general mixture of electrolytes in a charged parallel-plate channel. We use the modified Poisson equation to model the ion-ion electrostatic correlations. We report two key findings. First, we show that, in a single monovalent or multivalent electrolyte, ion-ion electrostatic correlations can cause a unique reversal in the direction of diffusioosmosis. Second, we show that, in a general mixture of electrolytes, the ionic strength at which the diffusioosmosis reversal occurs can shift by tuning the concentration of the individual electrolyte. The mathematical model developed here can be used to design diffusioosmosis, which is central to applications such as species separation, enhanced oil recovery, and blue energy harvesting.