  The present study reports experiments of water droplet impacting on ice or on
a cold metallic substrate, with the aim of understanding the effect of phase
change on the impingement process. Both liquid and substrate temperatures are
varied, as well as the height of fall. The dimensionless maximum spreading
diameter, $\beta_m$, is found to increase with both temperatures as well as
with the impact velocity. Furthermore, $\beta_m$ is reduced when
solidification, which enhances dissipation, is present, whereas fusion favours
the liquid film spreading. These observations are rationalized by extending an
existing model of effective viscosity, in which phase change alters the size
and shape of the developing viscous boundary layer, thereby modifying the value
of $\beta_m$. The use of this correction allows to adapt a scaling law existing
for isothermal drop impacts to propose a universal law giving the maximum
diameter of an impacting water droplet in the presence of melting or
solidification.
