Theoretical and experimental investigation of ultrasonic wave propagation in suspensions of particles: effects of concentration and polymer modification

Ultrasound has been used as a Non-Destructive Testing method for colloids for characterising or monitoring purposes. The principle of ultrasound characterisation is based on measurements of ultrasound propagation in the tested sample, followed by interpretation of the experimental data using scattering models. One of the commonly used models is the single scattering model of Epstein and Carhart and Allegra and Hawley, which is often combined with the multiple scattering approach developed by Lloyd and Berry to account for the particle interactions in the acoustic field. These models have proved successful in application to dilute colloidal systems, but they are known to break down in highly concentrated systems due to non-acoustic field interactions. There are also situations where the particles to be characterised have unusual structures, such as hybrid particles with polymer modification on their surface. These particles have growing interest due to the potential application of their smart surface . The core-shell model by Anson and Chivers, has been shown to have some success in predicting the ultrasonic behaviour of such particles. However, the original core-shell model is a complicated model, which can be ill-conditioned under certain conditions and therefore limiting the application of this model. In order to address the issues above, the primary aim of this research was to develop and validate models for ultrasonic propagation in concentrated nano-suspensions and suspensions of particles modified with polymers. The limits of applicability of the classic ECAH/LB model for highly concentrated suspensions in the nano-scale was explored experimentally. The new model developed by Forrester and Pinfield was studied as a solution to interpret shear interactions between particles in concentrated suspensions. An analytical approximation was derived for the core-shell model and validated. The analytical solution was compared both analytically and numerically with Anson and Chivers full matrix model and the ECAH model. The possibility of applying the ultrasonic technique to core-shell nano-particles was investigated, and the core-shell model was validated experimentally with polymer-modified particle suspensions.