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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) Schematic procedures for fabricating superhydrophobic and slippery liquid infused SiC/Si hierarchical structures. (b) Static water contact angle (CA) transitions of bare, PTFE- coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures. (c) Water sliding angle (SA) transitions of bare, PTFE-coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures.
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f2: (a) Schematic procedures for fabricating superhydrophobic and slippery liquid infused SiC/Si hierarchical structures. (b) Static water contact angle (CA) transitions of bare, PTFE- coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures. (c) Water sliding angle (SA) transitions of bare, PTFE-coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures.

Mentions: The surface wettability control process of as-synthesized surfaces is depicted in Fig. 2a. Theas-synthesized bare SiC nanowire arrays and SiC/Si hierarchical structures both showed superhydrophilic properties with static water contact angles (CAs) below 5°and water sliding angles (SAs) of ~90° (Fig. 2b,c). This hydrophilicity is due to the hydrophilic -OH groups of the SiO2 layers that formed on the SiC surfaces during the thermal reaction process. The bare Si micropost samples showed a moderate hydrophilic wettability with water CAs of ~50° and water SAs of ~90°. To reduce the surface energy and make the surfaces hydrophobic, a polytetrafluoroethylene (PTFE) solution was spin coated on the sample surfaces. Due to the C-F chains of PTFE, the self-assembled-monolayer (SAM) layer of PTFE coatedon the surfaces exhibited a high water repellency. The water CAs ofthe SAM-modified SiC nanowire arrays and SiC/Si hierarchical structures were 154° and 164°, respectively, which shows their superhydrophobicity. The SiC/Si hierarchical structure was extremely superhydrophobic due to the enhanced surface roughness. Also both sample surfaces had water SAs below ~3° showing their very low adhesion affinity with water droplets. The PTFE-coated Si micropost arrays showeda moderate hydrophobicity with water CAs of 114° and water SAs of 35° due to the lack of the surface roughness. As a reference of comparison with other hierarchical nanostructure, PTFE-coated ZnO/Si hierarchical structures were prepared. In the case of theZnO/Si hierarchical structure, rather short ZnO nanorods grew on the Si microposts; the experimental details and SEM images are presented in the Supplementary Fig. 2. These PTFE-coated ZnO/Si hierarchical structures also showed superhydrophobicity with water CAs of 163° and water SAs of 2.5°.


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) Schematic procedures for fabricating superhydrophobic and slippery liquid infused SiC/Si hierarchical structures. (b) Static water contact angle (CA) transitions of bare, PTFE- coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures. (c) Water sliding angle (SA) transitions of bare, PTFE-coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: (a) Schematic procedures for fabricating superhydrophobic and slippery liquid infused SiC/Si hierarchical structures. (b) Static water contact angle (CA) transitions of bare, PTFE- coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures. (c) Water sliding angle (SA) transitions of bare, PTFE-coated (superhydrophobic) and lubricant injected (slippery liquid infused) SiC nanowire arrays, Si micropost arrays, SiC/Si hierarchical structures and ZnO/Si hierarchical structures.
Mentions: The surface wettability control process of as-synthesized surfaces is depicted in Fig. 2a. Theas-synthesized bare SiC nanowire arrays and SiC/Si hierarchical structures both showed superhydrophilic properties with static water contact angles (CAs) below 5°and water sliding angles (SAs) of ~90° (Fig. 2b,c). This hydrophilicity is due to the hydrophilic -OH groups of the SiO2 layers that formed on the SiC surfaces during the thermal reaction process. The bare Si micropost samples showed a moderate hydrophilic wettability with water CAs of ~50° and water SAs of ~90°. To reduce the surface energy and make the surfaces hydrophobic, a polytetrafluoroethylene (PTFE) solution was spin coated on the sample surfaces. Due to the C-F chains of PTFE, the self-assembled-monolayer (SAM) layer of PTFE coatedon the surfaces exhibited a high water repellency. The water CAs ofthe SAM-modified SiC nanowire arrays and SiC/Si hierarchical structures were 154° and 164°, respectively, which shows their superhydrophobicity. The SiC/Si hierarchical structure was extremely superhydrophobic due to the enhanced surface roughness. Also both sample surfaces had water SAs below ~3° showing their very low adhesion affinity with water droplets. The PTFE-coated Si micropost arrays showeda moderate hydrophobicity with water CAs of 114° and water SAs of 35° due to the lack of the surface roughness. As a reference of comparison with other hierarchical nanostructure, PTFE-coated ZnO/Si hierarchical structures were prepared. In the case of theZnO/Si hierarchical structure, rather short ZnO nanorods grew on the Si microposts; the experimental details and SEM images are presented in the Supplementary Fig. 2. These PTFE-coated ZnO/Si hierarchical structures also showed superhydrophobicity with water CAs of 163° and water SAs of 2.5°.

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.