  We show that particle roughness leads to changes in the number, shape and
resulting capillary force of liquid bridges in capillary suspensions. We
created fluorescently labeled, raspberry-like particles with varying roughness
by electrostatically adsorbing silica nanoparticles with sizes between 40 nm
and 250 nm on silica microparticles. Rougher particles require more liquid to
fill the surface asperities before they form pendular bridges, resulting in
smaller and weaker bridges. In a system where the effective bridge volume is
adjusted, higher particle roughness leads to less clustered networks, which
show a higher yield strain for a matching storage modulus compared to the
smooth particle networks. This finding suggests that the particle-particle
frictional contacts also affects the strength of capillary suspensions. Using
asymptotically nonlinear oscillatory rheology, we corroborate the non-cubical
power law scaling of the third harmonic in the shear stress response that
results from both Hertzian contacts and friction between particles connected by
capillary bridges. We demonstrate that the repulsive Hertzian contact parameter
$A$ is sensitive to the liquid bridge strength and that roughness appears to
shift the relative scaling of the power law exponents from adhesive-controlled
friction to load-controlled friction.
