(56b) Visualisation of Mass Transfer across an Electrically Charged Plane Interface

The intensification of liquid-liquid transport processes using externally applied electric fields is well known. The presence of electric charges or local variations on their surface density will result in local variations in the effective interfacial tension and thus lead to interfacial tension induced surface turbulence (Maragoni instability). Such phenomena increases mass transfer rate. Promotion of interfacial disturbance is especially interesting because a number of novel liquid-liquid systems such as those involving homogeneous catalysts, or involving enzymes which are inter-facially active potentially could be intensified by the application of electrical fields. This paper is concerned with the fundamental interfacial mechanisms behind the observed increase in mass transfer across a plane interface in the presence of an electric field. Experimental study of this for some real liquid-liquid systems is presented, and a novel technique for measuring the rate of interfacial mass transfer is described. Schlieren technique was utilized to record visually the hydrodynamic disturbances in the vicinity of the liquid-liquid interface. The following experimental variables are included in the study: The electrical charge on the plane interface; the magnitude and direction of the external electrical field; viscosity and interfacial tension of the system; the presence of surface active agents. Simultaneously, finite element modelling of interfacial mass transfer was used to predict significant time-dependent convective disturbances at the liquid-liquid interface.