Electroacoustic characterization of bidisperse suspensions

Electroacoustic techniques are promising tools for the size determination and electrokinetic characterization of concentrated colloidal suspensions. When particles are not homogeneous in size and/or density, the dynamic mobility obtained is a kind of average of the mobilities of every particle. In this paper, we try to discern which averaging procedure provides a better description of the dynamic mobility of bidisperse suspensions consisting of a mixture of two very different types of particles. The results show that the amplitude of the sound wave induced by an applied ac field (electrokinetic sonic amplitude) is not just the sum of the amplitudes of the waves generated by every particle but has a larger contribution from the larger particles, although the small size entities considerably influence the behaviour of the latter because of their interference in the fluxes of the fluid and ions around them.