Concentration dependence of electrokinetic transport coefficients of non-aqueous binary mixtures through weakly charged porous plugs

Abstract

An experimental investigation of the concentration dependence of electrokinetic transport coefficients of methanol + ethanol mixtures through a quartz plug is described. Electro-osmotic flow and streaming-potential measurements have been carried out. The Onsager reciprocity relations have been experimentally checked for all compositions of the binary mixture used. The form of the fluidity curve indicates that the ethanol + methanol mixture is a quasi-ideal system with a small negative deviation. The hydrodynamic permeability of systems comprising methanol + ethanol mixtures and a porous plug and the fluidity of the mixture vary with the composition in a similar way. The variation of the cross-phenomenological coefficient with composition is due to an analogous variation of the term Dζ/η with the mole fraction of methanol. On the other hand, the ratio of streaming potential to pressure difference (in the interval 0–20 cmHg) decreases as the pressure drop increases. This result agrees with the theoretical findings of Rutgers and Boumans concerning the effect of turbulence on the streaming potential. The concentration dependence of the second-order coefficients has been partially explained on the basis of Jha's equations.