Experimental verification of nanofluid shear-wave reconversion in ultrasonic fields

What is it about?

This work demonstrates for the first time new phenomena in the ultrasonic scattering in nanofluids. We show that shear-mode effects cannot be neglected as one approaches the nanoscale and their complex dependencies upon particle size, concentration, applied frequency, and density contrast between the suspended particles and the suspending medium are carefully investigated. We use two ultrasonic spectrometers (a Digusonic DSX and a Malvern Ultrasizer) and compare the result to our new multiple scattering model, which is very computationally efficient, making it ideal for implementation in particle characterisation and sizing systems (especially for suspensions that are optically opaque and impossible to analyse using traditional light scattering techniques) . Indeed, our model is very successful even at high concentrations (tested up to 25% volume/volume) where other models break down. Without inclusion of shear-wave reconversion effects the attenuation is found to be much higher than experimental observation. Our model matches experimental results almost exactly in the frequency ranges investigated (1-20MHz, which is the range valid for medical and biological analyses). In this frequency regime previous multiple scattering models have failed at comparatively low concentrations and at the lower range of the frequency scale, whereas we find that the new model very accurately matches the experiments. We examine in detail silica particles of 100nm, 214nm, 430nm and 1000nm in water suspensions and measure the attenuation over the broadband of frequencies and concentrations.

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