4. Conclusions
This study has shown categorically that microwave heating
results in enhanced droplet coalescence of the water phase in
water-in-oil emulsions. Microwave heating results in an order of
magnitude improvement in separation time, with the lowest heating
times occurring with saline emulsions. Saline emulsions separate
more rapidly due to the change in dielectric properties and the
change in interfacial tension, which promotes a larger thermal gradient
and improved probability of coalescence. The improvements
in settling rate can all be rationalised by the unique thermal gradients
that arise from microwave heating, and their subsequent impact
on viscosity and interfacial tension at the droplet/oil interface.
Contrary to other reports in the literature, no evidence for nonthermal
effects was observed in this study.