Simulation of self-assembly in an evaporating droplet of colloidal solution by dissipative particle dynamics

A method of Brownian dissipative dynamics of charged colloidal nanoparticles in microdroplet of solution deposited on plane substrate is proposed for investigation of self-assembly and self-ordering of colloids during solute evaporation. Method is based on the numerical solution of multi-scale Langevin equation for each particle, the hydrodynamic microflows approach, and droplet evaporation model. The method takes into account the DLVO-forces between the particles, their interaction with the substrate (adhesion, friction, roughness); Stokes’, Brownian, and capillary forces (wetting and depinning, outflow angles, surface tension). The self-assembled pattern morphology dependence on the model parameters is investigated. The nature of coffee ring effect was studied. It is shown that the hexagonal domain ordering of particles ensemble in pattern can be formed onto plane substrate as a result of interparticle repulsion and the capillary compression during evaporation of solvent. Numerical results are in good agreement with experiments on self-assembly in colloidal droplet deposited by inkjet technology.