Experimental study of sound attenuation in quasi-monodisperse emulsions

Very narrow size distribution oil-in-water emulsions have been prepared by using a recently proposed selective creaming method. The emulsions have been characterized by static and dynamic light scattering measurements. The ultrasonic absorption of the emulsions has been measured with an acoustic interferometer at frequencies between 0.5 and 10 MHz for a wide range of concentrations and droplets sizes. The comparison of the experimental results with existing theories shows an excellent agreement at oil volume fractions up to 0.15. The discrepancy between theory and experiments observed at higher volume fractions is attributed to thermal interactions between droplets for which a semi-quantitative model is proposed.