On electroosmosis and related phenomena

Electroosmosis through a Cation-Exchange Membrane: Effect of an ac Perturbation on the Electroosmotic Flow

Electroosmosis experiments through a cation-exchange membrane have been performed using NaCl solutions in different experimental situations. The influence of an alternating (ac) sinusoidal perturbation, of known angular frequency and small amplitude, superimposed to the usual applied continuous (dc) signal on the electroosmotic flow has been studied. The experimental results show that the presence of the ac perturbation affects the electroosmotic flow value, depending on the frequency of the ac signal and on the solution stirring conditions. In the frequency range studied, two regions have been observed where the electroosmotic flow reaches a maximum value: one at low frequencies ( approximately Hz); and another at frequencies of the order of kHz. These regions could be related to membrane relaxation phenomena. Copyright 2000 Academic Press.

Electroosmotic Transport through a Cation-Exchange Membrane: Effect of the Stirring on the Dependence of the Electroosmotic Permeability on the Temperature

The electroosmotic flux through a cation-exchange membrane has been obtained in different situations. From these measurements, the apparent electroosmotic permeability, W, of a cation-exchange membrane has been determined as a function of the temperature, T, and the stirring rate, v, of the solutions. In all the experimental situations studied, W decreases when v increases, while it can increase or decrease with T depending on the temperature range considered. For this last reason, the (T,W) curves show a minimum whose value and position depend on the experimental conditions established. The influence of the concentration polarization effect in the value of W and in its dependence with v and T is studied and quantified. Copyright 1999 Academic Press.

Effect of the Temperature on the Electroosmotic Permeability of a Cation-Exchange Membrane

The water electroosmotic flux, JV, through a cation exchange membrane has been measured as a function of the temperature, T, with various values of the electrolyte concentration and for different current densities. From these measurements the electroosmotic permeability, W, of the membrane has been determined under different experimental conditions. In the studied temperature range, 282 K </= T </= 308 K, a clear dependence of W on T was observed, so that, W decreases when T increases at the lowest values of T, whereas the opposite behavior occurs at the highest values of T. For this reason the (T, W) curves show a minimum in most of the studied cases. The position of this minimum as well as the value of the minimum of the electroosmotic permeability depends clearly on the concentration and the current density. Copyright 1997 Academic Press. Copyright 1997Academic Press