Manipulating the three-phase contact line of an evaporating particle-laden droplet to get desirable microstructures: A lattice Boltzmann study

Abstract

The lattice Boltzmann method (LBM) is used to study a novel inkjet printing scheme for making three-dimensional (3D) microstructures from evaporating droplets laden with the nanoparticles. The scheme involves pinning the three-phase contact line (TCL) on the specific points of a chemically heterogeneous pattern, leading to an asymmetric retraction of the TCL and a corresponding particle deposition morphology. A simple isothermal LBM model incorporating diffusion-limited evaporation, contact line pinning, and an Eulerian treatment of particles is employed to study the said scheme. The results show that TCL retraction plays a significant role in determining the final shape of the pattern when the particle concentration is low (com.elsevier.xml.ani.Math@5a3f1a95), enabling a pure liquid approach to approximate the deposition. For the particle Peclet number greater than one, the coffee-ring effect leads to undesirable non-uniform deposits close to the pinning regions. Increasing the pattern dimensions and the surface energy difference between the pattern and the substrate result in a more stereoscopic morphology. The shape of the pattern and the pinning points can be altered to control the shape and the dimensions of the final 3D microstructure. A premature unpinning of the pure liquid drop is observed at the sharp edges of the pinning points owing to the higher contact line curvature in that region.