Evaporation induced self-assembly of rough colloids: A multiscale simulation study

Abstract A multiscale simulation method combining the finite volume multiphase Volume of Fluid (VOF) method and Dissipative Particle Dynamics (DPD) is employed to investigate and control the self-assembly of charged polymeric nanoparticles in droplet solution deposited on a plane and rough substrate during solvent evaporation. The sessile droplet is placed on a constant temperature substrate and allowed to evaporate as the particles self-assemble at the bottom. The droplet temperature drops to the wet-bulb temperature during evaporation as expected. A coupling scheme between the VOF and the Level Set (LS) parameters is presented to reduce the spurious current in the droplet. An algorithm is presented for combining the coupled VOF and LS method with the DPD method. The DPD simulation includes the Derjaguin–Landau–Verwey–Overbeek (DLVO) forces between the particles, their interaction with the substrate, Stokes drag, Brownian, and capillary forces. Ring formation of particles for different contact angles is discussed in terms of ring width and deposition time. The effect of van der Waals (vdW) force and substrate friction on particle deposition are discussed. A uniform deposit is obtained with a combination of moderate vdW force and surface friction. By applying the First Order Statistics analysis, three stages of deposit development are observed for various contact angles. The proposed simulation method is very general and can provide valuable tools for controlling and optimizing the self-assembly of nanoparticles.