|M.Sc Student||Abo Jabal Mohammad|
|Subject||Forced sliding of volatile drops: formation of|
|Department||Department of Chemical Engineering||Supervisors||Professor Alexander Leshansky|
|Professor Hossam Haick|
|Full Thesis text|
The motion of droplets on solid surfaces is fundamental to many technological processes and applications, such as painting, coating, printing, patterning of various nano-metric species and others.
We have studied different flow regimes and deposition patterns seen with volatile droplets moving over inclined solid substrates. Two types of volatile droplets were investigated: single component droplets and binary solution droplets. Binary solution droplets are characterized either by inward Marangoni (solute-capillary) flow or outward Marangoni flow, depending on a surface tension change due to lowering of the concentration of the fast evaporating component.
At wide range of capillary numbers (, measuring the relative importance of viscous and surface tension forces), both the single component and outward Marangoni flow droplets exhibit similar behavior, are characterized by the spreading regime. Short-film spreading is obtained at low, whereas long-film spreading is found at higher. Inward Marangoni flow droplets behave differently, a metastable corner shape droplet observed at smaller than a specific , at which the so-called micro-rivulet (µ-R) regime is observed which is of particular interest towards patterning nanometric species.
We carried out a detailed experimental study of the µ-R formation in different binary solutions. The directionality and intensity of the Marangoni flow was controlled by vapor composition in a sealed chamber enclosing the sliding binary droplets. The µ-R formation in a certain range of Ca proved to be a universal phenomenon subject to the occurrence of inward Marangoni flow. We propose a simplified mathematical model for the shape of µ-R based on the lubrication approximation. The resulting µ-R profile shows a good agreement with the experimental results.