  We study the stress developed during the drying of a colloidal drop of silica
nanoparticles. In particular, we use the wrinkling instability of a thin
floating sheet to measure the net stress applied by the deposit on the
substrate and we focus on the effect of the particle polydispersity. In the
case of a bidisperse suspension, we show that a small number of large particles
substantially decreases the expected stress, which we interpret as the
formation of lower hydrodynamic resistance paths in the porous material. As
colloidal suspensions are usually polydisperse, we show for different average
particle sizes that the stress is effectively dominated by the larger particles
of the distribution and not by the average particle size.
