title: Schemes for the fragmentation and merging of droplets resting on a solid substrate using a patterned wettability gradient.
abstract: A methodology has been proposed for the breakup and joining of water drops over a solid surface by varying its wettability gradient. A computational scheme using diffuse interface based smoothed particle hydrodynamics has been employed to simulate the droplet dynamics as the proof of the concept. For both the joining and breakup of drops, Y shaped patterns with the same or different wettability gradient along its different arms have been proposed. The breakup of a drop at the junction of the Y joint may be achieved if it is subjected to pulling forces along both of the branch arms. The pulling force can be brought into existence by providing an appropriate wettability gradient along the branches. By a proper selection of the branch orientation and the wettability gradient along them, it is possible to break a drop into two droplets of equal or unequal size. It has also been demonstrated that a drop can be broken into three small droplets by a specially designed four junction pattern of wettability on the solid surface. A Y junction has also been used for the merger of two drops. For this, two water drops placed at the end of the two branches are made to move toward the junction due to the gradient of contact angle. At the junction, they collide and merge into a single drop. A scheme has also been described where a combination of Y patterns can be exploited to generate a multitude of drops of different size.
authors.affiliation: Department of Mechanical Engineering, IIT Guwahati, 781039, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Das
authors.forename: P K
authors.initials: PK
authors.lastname: Das