  The breakup dynamics of viscous liquid bridges on solid surfaces is studied
experimentally. It is found that the dynamics bears similarities to the breakup
of free liquid bridges in the viscous regime. Nevertheless, the dynamics is
significantly influenced by the wettability of the solid substrate. Therefore,
it is essential to take into account the interaction between the solid and the
liquid, especially at the three-phase contact line. It is shown that when the
breakup velocity is low and the solid surface is hydrophobic, the dominant
channel of energy dissipation is likely due to thermally activated jumping of
molecules, as described by the Molecular Kinetic Theory. Nevertheless, the
viscous dissipation in the bulk due to axial flow along the bridge can be of
importance for long bridges. In view of this, a scaling relation for the time
dependence of the minimum width of the liquid bridge is derived. For high
viscosities, the scaling relation captures the time evolution of the minimum
width very well. Furthermore, it is found that external geometrical constraints
alter the dynamic behavior of low and high viscosity liquid bridges in a
different fashion. This discrepancy is explained by considering the dominant
forces in each regime. Lastly, the morphology of the satellite droplets
deposited on the surface is qualitatively compared to that of free liquid
bridges.
