NON-EQUILIBRIUM THERMODYNAMIC STUDIES OF ELECTRO-KINETIC EFFECTS-X ETHYLENEGLYCOL + WATER MIXTURES

Abstract

Experimental results for the measurement of electro-osmosis, electro-osmotic pressure difference, streaming potential for ethyleneglycol-water (EG - H2O) mixtures (30%, 40%, 50%, 60% and 70% by weight) using pyrex sintered disc (G3) as a membrane at temperatures 25° to 40°C and at voltages 0-300 volts are reported. The data are analysed in the light of the theory of non-equilibrium thermodynamics. Attempts have been made to explore the domain of validity of linear phenomenological relations in the case of these mixtures. It has been found that the validity of the theory increases with the increase in the viscosity of the mixture and decreases with the increase in the dielectric constant of the mixture. The higher order co-efficients introduced owing to the non-validity of the linear phenomenological relations have been estimated from the data on electro-osmosis and electro-osmotic pressure difference. It is found that higher order straight co-efficients do not contribute effectively to the non-linearity of the relations. Onsager's reciprocity relations have been found to hold for all the mixtures reported here. It has been found that concentration dependence of the co-efficient, L22, representing the volume flow per unit pressure difference and the co-efficient, L21 or L12 representing the electro-osmotic velocity do not conform to Spiegler's frictional model. Efficiency of electro-kinetic energy (E) for electro-osmotic flow has been calculated and the results have been found to be in accordance with the non-equilibrium thermodynamic theories. For different compositions of EG - H2O mixtures at 25°C (E)max was obtained at half the value of electro-osmotic pressure difference.