The microwave absorption of emulsions containing aqueous micro- and nanodroplets: A means to optimize microwave heating

The microwave absorption at frequencies between 10 MHz and 4 GHz is measured for aqueous brine droplets dispersed in a dielectric medium ( ε ′ = 2.0 ). By varying the size of the droplets, ion type and ion concentration, it is found that the microwave absorption goes through a maximum which depends on the type of ions and their concentration. The absorption process is attributed to the polarization of the microdroplets through surface charges. Means to optimize microwave heating in emulsions is discussed. The dielectric relaxation of water-in-oil droplets was analyzed in dependence of droplet size and salt content. Strong surface polarization was found for droplets in the micrometer range.