Multi-ion diffusiophoresis.
The movement of charged particles occurs in a salt concentration gradient by the mechanism of diffusiophoresis. Current analytical models for diffusiophoresis have been developed for a gradient generated by a symmetric Z:Z electrolyte at steady state. Recently, our lab has reported diffusioosmotic flows due to dissolving calcium carbonate (CaCO3) which generates three ions (Ca(2+), HCO3(-), and OH(-)), and this fluid motion cannot be described by current analytical models. In this communication, we derive an expression for the diffusioosmotic flow in a gradient involving multiple ions of different valences, assuming infinitesimally thin double layers. We also solve numerically the time-dependent concentration profiles for the three-ion case and find that the concentration profile of HCO3(-) is non-monotonic in solution. Finally, we examine quantitatively the assumption of electroneutrality in solution, finding that electroneutrality is a good approximation even for the multi-ion case, indicating that our electric field derived from the ion migration equation is quite accurate.
The Pennsylvania State University, Department of Chemical Engineering, University Park, PA 16802, USA.
Tso-Yi
TY
Chiang
The Pennsylvania State University, Department of Chemical Engineering, University Park, PA 16802, USA. Electronic address: velegol@psu.edu.
Darrell
D
Velegol
Diffusiophoresis; Electroneutrality; Multi-ion diffusiophoresis