76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023;
Washington, DC
Session ZC03: Impact, Bouncing, Wetting and Spreading
12:50 PM–3:00 PM,
Tuesday, November 21, 2023
Room: Ballroom C
Chair: ANIK TARAFDER, George Washington University
Abstract: ZC03.00002 : Droplet impact of the ultrathin oil layer on smooth hydrophobic surfaces
1:03 PM–1:16 PM
Abstract
Presenter:
Shubham S Ganar
(Indian Institute of Technology Goa)
Authors:
Shubham S Ganar
(Indian Institute of Technology Goa)
Arindam Das
(Indian Institute of Technology (IIT) Goa)
This experimental study investigates the impact of water droplets on thin layers of oil covering different smooth hydrophobic surfaces. The selected oil and surface chemistry combinations exhibited low and very high affinities towards solids in the presence of water. Surfaces with strong oil affinity {van-der-Waal film(vdw)} displayed distinct behavior compared to surfaces with low affinity when subjected to water droplet impacts on the oil-coated surfaces. Smooth hydrophobic surfaces were prepared by coating silicone wafers with a thin layer of low surface energy materials such as octadecyl trichlorosilane (OTS) and trichloro-perfluorooctyl silane (FS). Subsequently, a thin layer of low viscous oil was coated uniformly on the hydrophobic surfaces using the dip coating method. Selected oil produced a very thin van-der-Waal (vdw) oil layer on the OTS functionalized surface and a thin non-vdw oil layer on the FS functionalized surface. High-speed imaging cameras and image analysis methods were used to analyze the impact dynamics. The findings reveal a complex series of events during droplet impact, with initial deformation of the oil film causing droplets to rebound due to repulsion between water and the oil-coated surface. Measurements of interfacial energies and contact angles indicated the cloaking of water drops by the oil film. Notably, droplet impact behavior changed significantly under repeated drop impacts on the same spot, attributed to variations in oil film thickness due to drainage on vdw oil-coated surfaces and a combination of oil drainage and oil barrier rupture on non vdw oil-coated surfaces. Additionally, viscosity and oil film thickness played crucial roles in determining impact outcomes. The study provides important insights, including droplet rebound on smooth OTS surfaces, droplet adhesion on vdw oil-coated OTS surfaces, the effect of viscous oils on impact dynamics, and the impact of oil film thickness on drop motion resistance and film rupture on non vdw oil-coated smooth surfaces. These findings have implications in various industrial and biomedical applications.