Detailed explanations for the occurrence and nature of interfacial phenomena in liquid–liquid systems on the basis of the theory of spontaneous surface convection

Abstract

The occurrence of unidirectional ejection phenomena (both continuous & intermittent), during mass transfer in binary and ternary systems respectively; reported earlier, have been explained on the basis of the theory of spontaneous surface convection (SSC). Also, intermittent jerking of the interface followed by emulsification coupled with profuse streaming action in the extract phase of two ternary systems has been explained by the same theory. In addition, intermittent circulatory motion in the extract phase only, in a ternary system has been explained on the basis of vertical and/or angular ejections’ restrained motion due to high viscosity of the extract phase. The theory of reversible adsorption and desorption phenomena for the transfer of surface-active solutes in ternary systems have been taken to help in justifying the occurrence of SSC during initial contacting of two phase. In most of the ternary systems reported earlier, vigorous density convection in the form of mushroom type density eddies observed are due to larger unstable density gradient. This is caused by high rates of mass transfer during SSC. SSC in the form of continuous circulatory motion in the extract phase only has been observed during the transfer of a surface inactive solute. Such phenomena occurred in aqueous to organic direction of transfer. The circulatory motion is due to ejections being against gravity. Surface inactive solute’s transfer also caused oscillatory motion of the interface as a whole in a particular system. The nature of most of the phenomena observed in binary and ternary systems appears to be due to molecular motions. The theory of SSC states that if specific energy of driving force of mass transfer is greater than free energy of the interface, interfacial instability occurs. It is probably a simplified version of a concept suggested here that can be explained by the kinetic theory as follows. It states that chemical potential difference of a solute between the two phases, if greater than the interfacial barrier plus molecular energy of the solute (in raffinate phase) then interfacial instability occurs. Thus, cluster of solute molecules in the form of ejections of bulk mass have been found to occur from raffinate to extract phase indicating high rates of mass transfer.

Keywords:

• Adsorption
• desorption
• ejection
• extraction
• instability
• interface

Acknowledgments

The main author of this paper, Prof. Amalesh Sirkar acknowledges the facility and support given (for experimental observations) by Prof. R. B. Mesler in his laboratory at the University of Kansas (USA) from 1970 to 1972.