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Bio-inspired dewetted surfaces based on SiC/Si interlocked structures for enhanced-underwater stability and regenerative-drag reduction capability.

Lee BJ, Zhang Z, Baek S, Kim S, Kim D, Yong K - Sci Rep (2016)

Bottom Line: Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency.These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%.Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

View Article: PubMed Central - PubMed

Affiliation: Surface Chemistry Laboratory of Electronic Materials, Department of Chemical Engineering, POSTECH (Pohang University of Science and Technology), Pohang, 790-784 Korea.

ABSTRACT
Drag reduction has become a serious issue in recent years in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. However, due to limited lifetime of plastron (i.e., air pockets) on superhydrophobic surfaces in underwater, the instability of dewetted surfaces has been a sticking point for practical applications. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

No MeSH data available.


(a) A scheme of drag reduction regeneration system. (b) Photocurrent density vs applied potential in dark and light states. The inset image shows the schematic energy gap structures of SiC/Si hierarchical structures for the hydrogen generation process. (c) Digital images demonstrating the generation of hydrogen gas bubbles in the dark and light. (d) Relative intensity transitions of SiC/Si hierarchical structures during regeneration of underwater superhydrophobicity by photoelectrochemical reaction. The inset image is a scheme for wetting and dewetting processes of SiC/Si hierarchical structures. (e,f) Relative intensity and velocity reduction (ΔV) transitions of SiC/Si hierarchical structures for several wetting and dewetting cycles.
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f5: (a) A scheme of drag reduction regeneration system. (b) Photocurrent density vs applied potential in dark and light states. The inset image shows the schematic energy gap structures of SiC/Si hierarchical structures for the hydrogen generation process. (c) Digital images demonstrating the generation of hydrogen gas bubbles in the dark and light. (d) Relative intensity transitions of SiC/Si hierarchical structures during regeneration of underwater superhydrophobicity by photoelectrochemical reaction. The inset image is a scheme for wetting and dewetting processes of SiC/Si hierarchical structures. (e,f) Relative intensity and velocity reduction (ΔV) transitions of SiC/Si hierarchical structures for several wetting and dewetting cycles.

Mentions: Although the superhydrophobic surfaces effectively reduce the drag force in water transport as mentioned above, they have limitations in real underwater applications due to the limited lifetime of the air interlayers. However, unlike SLIPS samples, superhydrophobic surfaces can be regenerated in underwater conditions. The lost underwater superhydrophobicity due to the collapse of the air interlayer could be restored by gas generation through photoelectrochemical (PEC) water splitting (Fig. 5a).The hydrogen gases generated by PEC reactions could be used to refill the lost air interlayer to restore superhydrophobicity. Figure 5b shows the photocurrent generation results for the PEC system with a SiC/Si hierarchical structure as a working electrode. The insulating SiO2 layers on the SiC/Si hierarchical structures were etched by HF treatment beforehand (Supplementary Fig. 4). All the PEC measurements were performed in a three-electrode PEC system with a Pt wire as a counter electrode and a saturated calomel electrode as a reference electrode under 1 Sun, AM 1.5 G illumination. The potential vs a reversible hydrogen electrode was analyzed using the Nernst equation and current density-potential (J-V) results were obtained. Because a p-type silicon substrate was used as the working electrode in our system, cathodic current generation occurred. Photogenerated electrons were used to reduce H+ ions to become H2 at the photocathode. Water was oxidized at the counter electrode. A schematic energy band diagram for our PEC system is displayed in the inset image of Fig. 5b. The digital images of Fig. 5c show the generation of gas bubbles in the dark and light. In the dark, the gas bubbles were not generated due to the absence of a light source. In contrast, exposure of light and high external bias (more than −2.0 V) on the samples resulted in the evolution of numerous gas bubbles on the surfaces.


Bio-inspired dewetted surfaces based on SiC/Si interlocked structures for enhanced-underwater stability and regenerative-drag reduction capability.

Lee BJ, Zhang Z, Baek S, Kim S, Kim D, Yong K - Sci Rep (2016)

(a) A scheme of drag reduction regeneration system. (b) Photocurrent density vs applied potential in dark and light states. The inset image shows the schematic energy gap structures of SiC/Si hierarchical structures for the hydrogen generation process. (c) Digital images demonstrating the generation of hydrogen gas bubbles in the dark and light. (d) Relative intensity transitions of SiC/Si hierarchical structures during regeneration of underwater superhydrophobicity by photoelectrochemical reaction. The inset image is a scheme for wetting and dewetting processes of SiC/Si hierarchical structures. (e,f) Relative intensity and velocity reduction (ΔV) transitions of SiC/Si hierarchical structures for several wetting and dewetting cycles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837397&req=5

f5: (a) A scheme of drag reduction regeneration system. (b) Photocurrent density vs applied potential in dark and light states. The inset image shows the schematic energy gap structures of SiC/Si hierarchical structures for the hydrogen generation process. (c) Digital images demonstrating the generation of hydrogen gas bubbles in the dark and light. (d) Relative intensity transitions of SiC/Si hierarchical structures during regeneration of underwater superhydrophobicity by photoelectrochemical reaction. The inset image is a scheme for wetting and dewetting processes of SiC/Si hierarchical structures. (e,f) Relative intensity and velocity reduction (ΔV) transitions of SiC/Si hierarchical structures for several wetting and dewetting cycles.
Mentions: Although the superhydrophobic surfaces effectively reduce the drag force in water transport as mentioned above, they have limitations in real underwater applications due to the limited lifetime of the air interlayers. However, unlike SLIPS samples, superhydrophobic surfaces can be regenerated in underwater conditions. The lost underwater superhydrophobicity due to the collapse of the air interlayer could be restored by gas generation through photoelectrochemical (PEC) water splitting (Fig. 5a).The hydrogen gases generated by PEC reactions could be used to refill the lost air interlayer to restore superhydrophobicity. Figure 5b shows the photocurrent generation results for the PEC system with a SiC/Si hierarchical structure as a working electrode. The insulating SiO2 layers on the SiC/Si hierarchical structures were etched by HF treatment beforehand (Supplementary Fig. 4). All the PEC measurements were performed in a three-electrode PEC system with a Pt wire as a counter electrode and a saturated calomel electrode as a reference electrode under 1 Sun, AM 1.5 G illumination. The potential vs a reversible hydrogen electrode was analyzed using the Nernst equation and current density-potential (J-V) results were obtained. Because a p-type silicon substrate was used as the working electrode in our system, cathodic current generation occurred. Photogenerated electrons were used to reduce H+ ions to become H2 at the photocathode. Water was oxidized at the counter electrode. A schematic energy band diagram for our PEC system is displayed in the inset image of Fig. 5b. The digital images of Fig. 5c show the generation of gas bubbles in the dark and light. In the dark, the gas bubbles were not generated due to the absence of a light source. In contrast, exposure of light and high external bias (more than −2.0 V) on the samples resulted in the evolution of numerous gas bubbles on the surfaces.

Bottom Line: Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency.These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%.Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

View Article: PubMed Central - PubMed

Affiliation: Surface Chemistry Laboratory of Electronic Materials, Department of Chemical Engineering, POSTECH (Pohang University of Science and Technology), Pohang, 790-784 Korea.

ABSTRACT
Drag reduction has become a serious issue in recent years in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. However, due to limited lifetime of plastron (i.e., air pockets) on superhydrophobic surfaces in underwater, the instability of dewetted surfaces has been a sticking point for practical applications. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

No MeSH data available.