  Water microdroplet impact at velocities up to 100 m/s for droplet diameters
from 12 to 100 um is studied. This parameter range covers the transition from
capillary-limited to viscosity-limited spreading of the impacting droplet.
Splashing is absent for all measurements; the droplets always gently spread
over the surface. The maximum spreading radius is compared to several existing
models. The model by Pasandideh-Fard et al. agrees well with the measured data,
indicating the importance of a thin boundary layer just above the surface, in
which most of the viscous dissipation in the spreading droplet takes place. As
explained by the initial air layer under the impacting droplet, a contact angle
of 180 degrees is used as model input.
