  As inkjet technology develops to produce smaller droplets, substrate features
such as accidental scratches or manufacturing defects can potentially affect
the outcome of printing, particularly for printed electronics where continuous
tracks are required. Here, the deposition of micro-droplets onto a scratch of
commensurate size is studied. The scratch is considered as a groove of
rectangular cross-section, with rectangular side ridges representing material
displaced from the substrate, and seven equilibrium morphologies are identified
as a result of inertial spreading, contact-line pinning, imbibition into the
scratch and capillary flow. A regime map is constructed in terms of scratch
depth and width, and theoretical estimates of the regime boundaries are
developed by adapting droplet spreading laws for flat surfaces to account for
liquid entering the scratches. Good agreement is seen with numerical results
obtained using a GPU-accelerated three-dimensional multiphase lattice Boltzmann
model validated against published experiments, and the influences of Reynolds
number, Weber number and advancing and receding contact angles are explored.
Negative and positive implications of the results for printing applications are
discussed and illustrated via multiple-droplet simulations of printing across
and along scratches.
