  In this article, we study the spreading of droplets of density-matched
granular suspensions on the surface of a solid. Bidispersity of the particle
size distribution enriches the conclusions drawn from monodisperse experiments
by highlighting key elements of the wetting dynamics. In all cases, the
relation between the dynamic contact angle and the velocity of the contact line
follows a similar relation as that of a simple fluid, despite the complexity
introduced by the presence of particles. We extract from this relation an
apparent wetting viscosity of the suspensions that differs from that measured
in the bulk. Dimensional analysis supported by experimental measurements yields
estimate of the size of the region inside the droplet where the value of the
dynamic contact angle depends on a balance of viscous dissipation and capillary
stresses. Depending on how particle size compares with this viscous cut-off
length seems crucial in determining the value of the apparent wetting
viscosity. With bimodal blends, the particle size ratio can be used to show the
effects of the local structure and volume fraction at the contact line, both
impacting the value of the corresponding wetting viscosity.
