Morphologies and dynamics of micro-droplet impact onto an idealised scratch

Abstract

As inkjet technology develops to produce smaller droplets, substrate features such as accidental scratches or manufacturing defects can potentially affect the outcome of printing, particularly for printed electronics where continuous tracks are required. Here, the deposition of micro-droplets onto a scratch of commensurate size is studied. The scratch is considered as a groove of rectangular cross-section, with rectangular side ridges representing material displaced from the substrate, and seven equilibrium morphologies are identified as a result of inertial spreading, contact-line pinning, imbibition into the scratch and capillary flow. A regime map is constructed in terms of scratch depth and width, and theoretical estimates of the regime boundaries are developed by adapting droplet spreading laws for flat surfaces to account for liquid entering the scratches. Good agreement is seen with numerical results obtained using a graphical processing unit-accelerated three-dimensional multiphase lattice Boltzmann model validated against published experiments, and the influences of Reynolds number, Weber number and advancing and receding contact angles are explored. Negative and positive implications of the results for printing applications are discussed and illustrated via multiple-droplet simulations of printing across and along scratches.

Discontinuous dewetting dynamics of highly viscous droplets on chemically heterogeneous substrates

“…[32][33][34] An in-house code is used, which implements the same multiphase model as described by Al-Ghaithi et al. 35 The basic concept is to build a simplified kinetic model which connects the essential physics of microscopic/mesoscopic processes so that the macroscopic averaged properties obey the desired macroscopic equation. 36 Molecular velocities in 3D space are represented by a set of 19 discrete velocities defining a lattice structure connecting uniformly spaced nodes.…”

“…The surface wettability is controlled by a geometric contact-angle model with controllable hysteresis properties. 35 The advancing and receding contact angles are defined for oil-wet and water-wet regions in the simulation 43 and the specific parameters are described in the relevant figure captions and associated text in Section 4.…”