Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO&lt;sub&gt;2&lt;/sub&gt;/Si/SiO&lt;sub&gt;2&lt;/sub&gt; Wafers for Green Desalination

Das, Ratul; Arunachalam, Sankara; Ahmad, Zain; Manalastas, Edelberto; Syed, Ali; Büttner, U.; Mishra, Himanshu

doi:10.3791/60583

Cited by 12 publications

(7 citation statements)

References 33 publications

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“…We also hope that our investigation on this widespread and unique insect will inspire rational designs of materials and processes across a wide spectrum of applications. Mushroom-shaped microtrichia of Halobates could inspire coating-free liquid repellence and the prolonged entrapment of air in micro-textures could unleash the potential of common materials in drag reduction [63][64][65][66] , mitigating cavitation 67 , and desalination 68,69 . Grooming strategies of Halobates might inspire new designs for preventing membrane fouling that commonly affect the efficiency of desalination processes 70,71 .…”

Section: Resultsmentioning

confidence: 99%

Superhydrophobicity and size reduction enabled Halobates (Insecta: Heteroptera, Gerridae) to colonize the open ocean

Mahadik

Hernández-Sánchez

Arunachalam

et al. 2020

Sci Rep

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Despite the remarkable evolutionary success of insects at colonizing every conceivable terrestrial and aquatic habitat, only five Halobates (Heteroptera: Gerridae) species (~0.0001% of all known insect species) have succeeded at colonizing the open ocean-the largest biome on earth. this remarkable evolutionary achievement likely required unique adaptations for them to survive and thrive in the challenging oceanic environment. For the first time, we explore the morphology and behavior of an open-ocean Halobates germanus and a related coastal species H. hayanus to understand mechanisms of these adaptations. We provide direct experimental evidence based on high-speed videos which reveal that Halobates exploit their specialized and self-groomed body hair to achieve extreme water repellence, which facilitates rapid skating and plastron respiration under water. Moreover, the grooming behavior and presence of cuticular wax aids in the maintenance of superhydrophobicity. further, reductions of their body mass and size enable them to achieve impressive accelerations (~400 ms −2) and reaction times (~12 ms) to escape approaching predators or environmental threats and are crucial to their survival under harsh marine conditions. These findings might also inspire rational strategies for developing liquid-repellent surfaces for drag reduction, water desalination, and preventing bio-fouling. The proliferation of invertebrate taxa in the ocean during the Cambrian explosion eventually led to their colonization on land, where insects first appeared ~479 million years (Myr) ago 1 to eventually dominate various terrestrial ecosystems 2,3. With an estimated ~5.5 million extant species 4 , insects comprise 80% of all known metazoans, making them the dominant animals on Earth 5. Despite their successful colonization of both terrestrial and aquatic habitats, only a small number of insects (~0.5% of total species) have been found in marine environments, mostly in nearshore habitats, with only a handful of Halobates (~0.0001% of insect species) ultimately colonizing the open ocean, the largest biome on Earth 6-8. Halobates is a member of the family Gerridae, which evolved nearly 55 Myr ago 6,9. Some 48 species of Halobates are known to occur in tropical and subtropical seas and oceans that cover more than 70% of the Earth's surface. Most of these species are found in mangrove and near-shore habitats and two even live in freshwater, whereas five live on the surface of the open ocean. The fact that only a mere 0.0001% of insect species were able to colonize the largest habitat on Earth indicates that there must have been formidable environmental challenges for oceanic Halobates to overcome in order to live there. Halobates most likely evolved from an estuarine or mangrove ancestor that was washed out to the sea and became adapted to survive in the open ocean 8,10. Freshwater relatives of sea-skaters are often found on placid water bodies such as small ponds, lakes or slow-flowing streams, whereas many tropical species can be found

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Section: Resultsmentioning

confidence: 99%

Superhydrophobicity and size reduction enabled Halobates (Insecta: Heteroptera, Gerridae) to colonize the open ocean

Mahadik

Hernández-Sánchez

Arunachalam

et al. 2020

Sci Rep

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“…Inspired by these insects, researchers have demonstrated that by carving mushroom-shaped microtexture pillars (21)(22)(23) and microcavities (17,(24)(25)(26)(27)(28) on surfaces, even intrinsically wetting surfaces can trap air when immersed in liquids. While the inherent wettability of materials dictates that the fully filled or the "Wenzel" state (29) should be the thermodynamic minima, air-filled or metastable "Cassie" states (30) can be engineered to persist for longer durations (31).…”

Section: Introductionmentioning

confidence: 99%

Mitigating cavitation erosion using biomimetic gas-entrapping microtextured surfaces (GEMS)

et al. 2020

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Cavitation refers to the formation and collapse of vapor bubbles near solid boundaries in high-speed flows, such as ship propellers and pumps. During this process, cavitation bubbles focus fluid energy on the solid surface by forming high-speed jets, leading to damage and downtime of machinery. In response, numerous surface treatments to counteract this effect have been explored, including perfluorinated coatings and surface hardening, but they all succumb to cavitation erosion eventually. Here, we report on biomimetic gas-entrapping microtextured surfaces (GEMS) that robustly entrap air when immersed in water regardless of the wetting nature of the substrate. Crucially, the entrapment of air inside the cavities repels cavitation bubbles away from the surface, thereby preventing cavitation damage. We provide mechanistic insights by treating the system as a potential flow problem of a multi-bubble system. Our findings present a possible avenue for mitigating cavitation erosion through the application of inexpensive and environmentally friendly materials.

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“…It is expected that in the near future, the design principles for GEMs might be scaled up using techniques such as 3-D printing . Currently, we are investigating applications of our gas-entrapping surfaces for mitigating cavitation damage 47 , desalination 46,52 , and reducing hydrodynamic drag.…”

Section: Discussionmentioning

confidence: 99%

Rendering SiO<sub>2</sub>/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

Arunachalam

Domingues

Das

et al. 2020

JoVE

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We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO 2 /Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (θ o < 90°) renders them even more wetting (θ r < θ o < 90°), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica θ o ≈ 40° for the water/air system, and θ o ≈ 20° for the hexadecane/ air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are θ r > 90°. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO 2 /Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (θ r ≈ 150°-160°) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within <1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

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Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO<sub>2</sub>/Si/SiO<sub>2</sub> Wafers for Green Desalination

Cited by 12 publications

References 33 publications

Superhydrophobicity and size reduction enabled Halobates (Insecta: Heteroptera, Gerridae) to colonize the open ocean

Superhydrophobicity and size reduction enabled Halobates (Insecta: Heteroptera, Gerridae) to colonize the open ocean

Mitigating cavitation erosion using biomimetic gas-entrapping microtextured surfaces (GEMS)

Rendering SiO<sub>2</sub>/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

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