Micro-PIV Study Of Apparent Slip Of Water On Hydrophobic Surfaces
The condition of no relative velocity of fluid past solid is termed as ‘no-slip boundary condition’. This condition is a general observation in fluid mechanics. However, several research groups have recently reported slip of water for surfaces with water repelling chemistry (referred to as hydrophobic surfaces). The effect has been attributed to disruption of H-bonding network of water molecules at such surfaces and resulting nucleation of dissolved gases and even reduced water density locally in absence of dissolved air. Slip of water on hydrophobic surfaces has been demonstrated to get amplified by high degree of roughness and patterning. Trapping of air in the surface asperities has been cited as the possible reason. The present work focuses on the study of effect of surface chemistry and roughness on flow behavior close to solid surfaces. Superhydrophobic surfaces have been generated by novel methods and wet-etching has been used to generate well-defined patterns on silicon surfaces. For flow characterisation, a micrometre resolution Particle Image Velocimetry (micro-PIV) facility has been developed and flow measurements have been carried out with a spatial resolution of less than 4 µm. It has been found from the experiments that flow of water on smooth surfaces, with or without chemical modification, conforms to the no-slip within the resolution limits of experiments. Deviation is observed in case of rough and patterned hydrophobic surfaces, possibly because of trapped air in asperities. Total Internal Reflection experiments, used to visualise the air pockets, confirmed the trapping of air at asperities. Diffusion of air out of the crevices seems to be the limiting factor for the utility of these surfaces in under-water applications.
Showing items related by title, author, creator and subject.
Pendyala, Prashant (2018-01-11)Surface roughness exists at many length scales-from atomic dimensions to meters. At sub-micron scale, the distribution of roughness is largely dependent on the process that generates the surface through the mechanisms of ...
Gupta, Rahul (2018-03-09)Dynamic behavior of impacting water drops on superhydrophobic solid surfaces provides important details on the stability/durability of such solid surfaces. Multi-scale surface roughness combined with a layer of low energy ...
Kannan, R (2014-09-08)The interaction of a liquid drop with a solid surface is being actively studied to understand practically encountered scenarios such as the impact of fuel spray droplets onto the walls of engine combustion chamber, the ...