Effect of the initial particle volume fraction on the structure of a drying colloidal deposit

[Display omitted] •For low volume fractions, below 10−4 (regime I), the capillary force breaks the colloidal structure.•Above 10−4 (regime II), the colloidal ring is rigid, pins the contact line and consequently keeps a hexagonal order. During the drying of a droplet on a substrate, dispersed colloidal particles are advected towards the contact line and then accumulate in its vicinity, forming in this way a ring-shaped deposit. Up to now, the structural properties at the particle scale of such pattern have been provided only by its final inspection at the end of the drying process. Here we follow all the stage of the ring formation, up to the complete drying, and for different particle volume fractions. We show that for low particle volume fractions, the final structure of the ring is always disordered, which results only from capillary attraction due to the deformation of the air-water interface. In contrast, for higher particle volume fractions, above 10−4, different consecutive rearrangements lead eventually to the formation of a ring with an ordered structure.