Dynamics of simultaneously impinging drops on a dry surface: Role of inhomogeneous wettability and impact shape

Hypothesis: The quality of the printed lines in applications such as ink-jet printing and additive manufacturing is affected by the interactions between the impinging drops. Impact shape and the inhomogeneity in surface wettability govern the spreading and recoiling dynamics of the interacting drops. Hence, understanding the role of these factors on the interaction dynamics is essential to optimize these applications. Numerical experiments: Phase-field based lattice Boltzmann method solver has been employed to investigate the interaction dynamics of two simultaneously impinging drops onto a dry surface. A geometry based contact angle scheme is used to model the moving contact line. Findings: Numerical simulations reveal that the previously identified interaction modes (Raman et al., 2017) are sensitive to the contact angle hysteresis, resulting in different impact outcomes. Two different interaction mechanisms have been discerned when drops impinge on a surface with a wettability gradient. It is shown that the deviation from the spherical geometry of the impact shape leads to different spreading behaviors and droplet morphology around the connecting region. With the increase in the cross-sectional aspect ratio, the interaction dynamics of oblate oblate combination is similar to its spherical counterpart, albeit at a faster recoiling rate. (C) 2018 Elsevier Inc. All rights reserved.