Hydrophobic particles inherently resist being suspended. Hydrophobic
particles might be regarded as tiny solid particles surrounded by a thin
gaseous shell. It has been hypothesised that hydrophobic particles act as
cavitation nuclei. This cavitation behaviour would explain the translation
speeds observed when hydrophobic polystyrene microspheres were driven through a
liquid medium by means of ultrasound.5 These translation speeds corresponded to
those observed with gas microbubbles of similar sizes.
If hydrophobic particles do have a thin gaseous layer surrounding the solid
cores, a sound field of sufficient pressure amplitude might force the gas layer
to form and inertial cavity and subsequently fragment during the collapse
phase. In this study, we investigated whether hydrophobic particles can be
forced to suspend by using ultrasound.
Hydrophobic particles of the materials C65 and ZnO can be forced to be
suspended in water using ultrasound. The high-speed observations confirm that
hydrophobic particles can act as cavitation nuclei. The lack of cavitation
after the first pulse indicates that the gas layer surrounding the hydrophobic
particle dissolves after inertial cavitation.Comment: 6 pages, 3 figures (7 frames), Submitted to the 39th Symposium on
UltraSonic Electronics (USE2019