Numerical simulations of capillary spreading of a particle-laden droplet on a solid surface

We present a direct numerical simulation technique and some results for the capillary spreading of a particulate droplet on a solid surface which is of great importance in the industrial inkjet printing technology as an alternative to the conventional lithography process for precise particle delivery. Since the spreading of particulate droplets is quite complicated in nature, the present work focuses on 2D capillary spreading behavior with full consideration of hydrodynamic interactions as a preliminary study for the particle effect on spreading. To understand the micro-structural phenomena underlying the process, we present a finite-element based computational scheme by combining the level-set method for an accurate interface description with the interfacial tension and the equilibrium contact angle, and the fictitious-domain method for suspended particles with implicit treatment of the hydrodynamic interactions. We investigated droplet spreading by capillary force in a Newtonian fluid and discussed effects of the presence of particles on the spreading behavior along with the particle movement. The amount of spread of a particulate droplet appears smaller than that of a homogeneous fluid droplet during the spread process and this reduced rate of spreading has been interpreted the results in conjunction with the distribution of the shear rate, the angular velocity of particles, and the kinetic energy. (C) 2009 Elsevier B.V. All rights reserved.