Morphologies and Dynamics of Micro-Droplet Impact onto an Idealised Scratch

• Published in: arXiv.org 2020-07
• Main Authors: Al-Ghaithi, Khaled H A, Harlen, Oliver G, Kapur, Nikil, Wilson, Mark C T
• Format: Article
• Language: English
• Subjects: Capillary flow; Computer simulation; Contact angle; Deposition; Droplets; Failure modes; Inkjet printing; Lattice vibration; Mathematical models; Substrates; Surface defects; Three dimensional models
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2007.01727

With the continued drive to smaller printed features using inkjet technologies, there is a growing impact of scratches and surface defects on the final print quality. With printed electronics, a growth area of application within inkjet printing, this can cause breaks in the continuity of circuits. Here, a validated, GPU-accelerated, 3D multiphase lattice Boltzmann model is used to elucidate the physics of droplet deposition into scratches of commensurate size to the droplets. For the geometrical class of scratch examined here, seven equilibrium morphologies of the final droplet are identified, highlighting the rich physical behaviour of the system. This is captured in a regime map, on which the influences of Reynolds and Weber numbers and advancing and receding contact angles are illustrated. Modelling droplet deposition dynamics identifies printing failure modes associated with the dimensions of the scratch causing a break in a line, or capillary flow along the scratch causing unintentional connections between printed parallel tracks. Subtle changes to operating parameters also suggest line continuity can be recovered, for example using a subsequent droplet to modify the position of the preceding one. Multiple-droplet simulations of printing along a scratch also show that deliberate scratch-like features on a substrate could be exploited to achieve uniform tracks.