Nano and submicron particle sizing in concentrated suspension by dynamic ultrasound scattering method

The ultrasonic spectroscopy method has long been known as a particle size analysis method applicable to concentrated particle suspensions that do not transmit light. On the other hand, it requires prior estimation of density and thermal parameters in addition to the parameters of the surrounding liquid. In this paper, we describe a method for precisely measuring diameter of nano and submicron particles in highly concentrated (similar to 30 wt%), optically turbid suspensions using dynamic ultrasound scattering (DSS). This method is an acoustic analogue of the dynamic light scattering (DLS) method, which determines the so-called Stokes-Einstein particle size by measuring the diffusion coefficient. Here, the only parameters required in the DSS analysis are the simultaneously measurable sound velocity of the suspension and the viscosity of the solvent (water), which is significantly less a priori information required. In addition, the required sample volume is only 50 mu L, which can easily accommodate precious samples. However, as the concentration increases, two effects cannot be ignored: interference from the particle structure (static structure factor) and long-ranged interaction (hydrodynamic interaction). This study focuses on the long-wavelength approximation of ultrasound, which has a longer wavelength than light, and the advantages of simplifying these complex interactions and providing a means to determine particle size by a different route than conventional ultrasonic methods. Finally, the advantages and disadvantages of this method are also discussed.