Lattice Boltzmann Simulation of Multiple Droplet Interaction on Non-ideal Surfaces for Inkjet Deposition

Inkjet deposition enables a more efficient, economic, scalable manufacturing process for a wider variety of materials than other traditional additive techniques. The interaction dynamics of inkjettted droplets on surfaces are crucial for controlling the formation of the printed patterns, the accuracy of which is critical to the functionalities of the printed device (e.g., electronics). However, little research has been reported on this front due to the prohibitive computational cost of simulating the dynamics of multiple droplet interaction on surfaces. Recently, Zhou et al. [1] reported an efficient numerical solver based on Lattice Boltzmann Method (LBM) that enabled the simulation of multiple droplet interaction dynamics on an ideal surface (i.e., smooth and homogeneous). In this model, the final shape of the droplets always relax back to the equilibrium shape (i.e., spherical cap) prescribed by the static contact angle of the idea surface, which does not provide any useful information on the final printed pattern. In order to simulate the printed pattern in real world, it is necessary to take into consideration of the contact angle hysteresis phenomenon on a non-ideal surface, which is caused by the surface roughness and chemical inhomogeneity of the surface. In this paper, a dynamic contact angle boundary condition is developed to take into account the contact angle hysteresis effect based on the previously reported LBM model. The improved LBM model was validated with experimental data from literature. The influence of the printing conditions, droplet spacing, and surface conditions on the two-droplet interaction dynamics were investigated with the validated LBM model. Interesting phenomena were observed and discussed. The interaction of a line of six droplets on a non-ideal surface was simulated to demonstrate the powerful capability of the developed numerical solver in simulating real-world inkjet printing process.