The spreading of liquid filaments on solid surfaces is
of paramount
importance to a wide range of applications including ink-jet printing,
coating, and direct ink writing (DIW). However, there is a considerable
lack of experimental, numerical, and theoretical studies on the spreading
of filaments on solid substrates. In this work, we studied the dynamics
of spreading of Newtonian filaments via experiment, numerical simulations,
and theoretical analysis. More specifically, we used a novel experimental
setup to validate a 2D moving mesh computational fluid dynamics (CFD)
model. The CFD model is used to determine the effect of processing
and fluid parameters on the dynamics of filament spreading. We experimentally
showed that for a Newtonian filament, the same spreading dynamics
and final shape are obtained when the initial radius is constant,
independent of the magnitude in printing parameters. In other words,
the only important parameter on the spreading of filaments is the
initial filament radius. Using a numerical model, we showed that the
initial filament radius manifests itself in two important dimensionless
parameters, Bond number, Bo, and viscous timescale, τμ. Furthermore, the results clearly show that the dynamics of spreading
are governed by the static advancing contact angle, θs. These three parameters determine a master spreading curve that
can be used to predict the spreading of cylindrical filaments on flat
substrates. Finally, we developed a theoretical model that was parameterized
using experimental data to correlate the steady-state shape of filaments
with Bo and θs. These results are particularly applicable
for predicting and controlling the dynamics of filaments in DIW and
other extrusion-based processes.