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 Dc/r,~ with the mole fraction of methanol. On the other hand, the ratio of streaming potential to pressure difference (in the interval 0-20cmHg) 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.

Streaming current, permeability, and microelectrophoresis of polystyrene latices in methanol–ethanol mixtures

“…This also suggests that the mixture properties can be responsible for the linear behavior reported for both mobility and streaming current. A similar dependence is found using the electroosmotic flow [10] (another electrokinetic method) through weakly charged porous plugs in methanol-ethanol mixtures. Excellent linear fits were reported in all the cases.…”

“…Such behavior can be interpreted on the basis of an increase in the dipolar moment due to the formation of hydrogen bonds in alcohol-alcohol mixtures. The linear decrease of the viscosity with the addition of the methanol molecules can be explained as a consequence of an increase in the free movement of the inner molecules, which is usually interpreted as a relaxation effect of hydrogen bonding between polar liquids such as methanol and ethanol [10]. The linear dependence of these methanol-ethanol properties makes the methanol-ethanol mixture an ideal liquid system.…”

Some Experimental Data Concerning the Effect of the Composition of Liquid Mixtures (Methanol-Ethanol) on the Electrophoretic Coefficient

“…These discrepancies are usually explained by the influence of the surface conductivity [4]. In our case, however, this effect cannot be involved since the contribution of the surface conductivity was negligible [15].…”

“…In earlier experiments we carried out streaming-potential measurements for similar systems [15] and the C-potential can also be arrived at from those measurements by using equation (8) figure 2. A significant difference can be seen between the CHS ar *d the ζ β (electrophoretic mobility) values: CHS is near to -20 mV, whereas ζ β is around -55mV.…”

“…The streaming-potential experimental results, with quartz porous plugs and methanol-ethanol mixtures, were shown in a previous paper [15]. The quartz and liquids used in those experiments were the same as those employed in the electrophoresis ones.…”