Influence of microwave pulsing patterns on oil/water interfacial behaviour

Abstract Demulsification is a fundamental process in many industries, including food, petroleum production and refining, with ongoing research into cheaper and more efficient processes. Microwaves have been considered as a low-cost and efficient method to speed demulsification: they can pass through the non-polar oil phase to be absorbed in the polar aqueous phase, effectively targeting the liquid-liquid interface. This study uses in-situ measurement of interfacial tension to investigate the effect of repeated short duration microwave irradiation on an oil-water interface in the presence of the non-ionic surfactant, Triton X-100. It was previously shown that a high energy concentration at the interface – achieved by microwave irradiation – resulted in rapid increases in interfacial tension. In this paper, the mechanism behind the change in interfacial tension induced by microwave irradiation is discussed: we propose that the rapid switching of the induced electromagnetic field causes disorder and desorption of surfactant adsorbed at the oil-water interface, leading to the short-term increase in interfacial tension. Management of the overall energy concentration is achieved by patterns of short-term pulsed irradiation to avoid boiling. The results indicate that disruption of the bonding network in the interfacial layer, and hence effective modification of interfacial tension, can be achieved by repeated irradiation of high power microwaves without leading to boiling. A previously discussed dimensionless number was used to characterise the extent of energy concentration at the interface in each experiment.