Acoustic spectroscopy studies of magnetic colloids: I. Determination of aggregate size distribution

The model describing a magnetic fluid as a dispersion of aggregates with di fferent sizes was considered. The aggregates consist of magnetic particles and a surfactant. In the simplest case, the aggregate is a particle covered with a stabilizing surfactant shell. The expressions for the velocity and the coefficient of the ultrasound attenuation in a magnetic fluid modeling by discrete and continuous aggregate size distributions are derived. The ca se is considered when the particle size distributions for the dispersed pha se is described by a log-normal function. For this case, distributions of t he aggregates' numbers, volumes, and surface areas over sizes were determin ed. The processed data on acoustic spectra for dodecane-based magnetic flui ds measured within the range of 12-2000 MHz at 20 degrees C are reported.