Characterisation of colloidal dispersions using ultrasound spectroscopy and multiple-scattering theory inclusive of shear-wave effects

What is it about?

Experimental analysis of ultrasonic effects and rapidly decaying shear waves in liquid when solid particle concentrations are high. Various frequencies and particle sizes are explored using ultrasonic spectroscopy

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Why is it important?

This work demonstrates for the first time new phenomena in the ultrasonic scattering in nanofluids and colloids in the frequency range 1-100MHz. The use of Ultrasonic spectrometry experimentally validates the regimes where the modelling is accurate. It demonstrates the use of our new multiple scattering theory for particle characterisation and we show that with the use of a modern spectrometer system coupled with the computationally efficient model, that process monitoring with ultrasonic systems has now reached maturity with these results. The technique is 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). 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 1-20MHz, with varying degrees of success dependent upon concentration, particle size and physical characteristics above this regime. However, in this frequency regime previous multiple scattering models have failed at comparatively low concentrations and at the lower end 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. This work is essential to help fulfil the potential for use of ultrasonic testing in nanofluids and colloids, showing the regimes where shear-modes have greatest effect. We expect the work to be of broad interest and for many new applications to emerge in ultrasonic monitoring and measurement.