  A simplified model is developed, which allows us to perform computer
simulations of the particles transport in an evaporating droplet with a contact
line pinned to a hydrophilic substrate. The model accounts for advection in the
droplet, diffusion and particle attraction by capillary forces. On the basis of
the simulations, we analyze the physical mechanisms of forming of individual
chains of particles inside the annular sediment. The parameters chosen
correspond to the experiments of Park and Moon [Langmuir 22, 3506 (2006)],
where an annular deposition and snakelike chains of colloid particles have been
identified. The annular sediment is formed by advection and diffusion
transport. We find that the close packing of the particles in the sediment is
possible if the evaporation time exceeds the characteristic time of
diffusion-based ordering. We show that the chains are formed by the end of the
evaporation process due to capillary attraction of particles in the region
bounded by a fixing radius, where the local droplet height is comparable to the
particle size. At the beginning of the evaporation, the annular deposition is
shown to expand faster than the fixing radius moves. However, by the end of the
process, the fixing radius rapidly outreaches the expanding inner front of the
ring. The snakelike chains are formed at this final stage when the fixing
radius moves toward the symmetry axis.
