Abstract
Air plastron in a superhydrophobic (SHPo) surface works as a lubricant that induces drag reduction on the surface. By air plastron, air is trapped between structures of the SHPo surface. However, air plastron is easily depleted by static water pressure or external flow conditions. Various nanostructures have been introduced to enhance the air stability of SHPo surfaces. In this study, the effects of such nanostructure on the air stability were experimentally investigated under high water pressure and flow conditions. Polyvinyl chloride solution was employed to form the nanostructure on the ridged SHPo surface. The critical pressure for the depletion of air plastron is 70% higher on SHPo surfaces introduced with the nanostructure than on surfaces without the nanostructure. Pressure drops (ΔP) in rectangular channels with the SHPo surface on the bottom side were measured to quantify the air stability under a flow condition. ΔP gradually decreases as the air plastron disappears on both SHPo surfaces. The hierarchical ridged surfaces with the nanostructure showed better air stability under static and flow conditions compared with the simple ridged surfaces without the nanostructure. The present results are helpful to understand the effects of the nanostructure on the air stability and its drag reduction mechanism.
Highlights
Frictional drag induces energy loss at various applications, especially marine vehicles used for transporting goods
The SHPo surface inspired by the special morphological structure of the lotus leaf11 has been widely adopted in various applications, such as self-cleaning,12 underwater bubble transport,13 anti-corrosion,14 anti-biofouling, anti-icing,15,16 and frictional drag reduction
The widths of all ridged surfaces were slightly decreased by nanostructure formation as summarized in Table S1 in the supplementary material
Summary
Frictional drag induces energy loss at various applications, especially marine vehicles used for transporting goods. The SHPo surface inspired by the special morphological structure of the lotus leaf has been widely adopted in various applications, such as self-cleaning, underwater bubble transport, anti-corrosion, anti-biofouling, anti-icing, and frictional drag reduction. Such SHPo surfaces lose the above functions, as air plastron on the surface is depleted by external forces, including high-pressure and high-speed flow.. The effects of nanostructure formation on ridgebased SHPo surfaces on the air stability and pressure drop (ΔP) were experimentally investigated. The effects of nanostructure formation on drag reduction and dynamic sustainability were experimentally investigated by measuring ΔP in a microchannel covered with the fabricated test surfaces
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