Drop impact of a concentrated colloidal suspension

The impact of drops of a concentrated colloidal suspension of nearly hard-core particles in octadecene (volume fraction: 59.6%) onto solid surfaces is studied experimentally by high-speed imaging, for impact Weber numbers ranging between 26 and 262, and for different values of the target surface energy. Upon impact, these drops do not exhibit inertial spreading, which is observed for other Newtonian and non-Newtonian fluid drops. On wettable surfaces (glass), impact is followed by capillary driven spreading at the same rate observed in Newtonian fluids (Tanner’s law), while on less wettable surfaces (PTFE) colloidal suspension drops relax to achieve the shape of a spherical cap, but do not spread. This peculiar impact morphology, and in particular the absence of inertial spreading, is interpreted as a consequence of dilatancy and jamming occurring upon impact.