Water-walking devices

Hu, David; Prakash, Manu; Chan, Brian; Bush, John W. M.

doi:10.1007/978-3-642-11633-9_12

Cited by 20 publications

References 29 publications

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“…This observation raises a number of interesting dynamical questions, including the role of the integument in detaching from the free surface. This class of problems is currently under consideration and is likely to inform the design of biomimetic water-walking devices (Hu et al 2003(Hu et al , 2007Suhr et al 2005; …”

Section: Discussionmentioning

confidence: 99%

The hydrodynamics of water-walking arthropods

2010

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We present the results of a combined experimental and theoretical investigation of the dynamics of water-walking insects and spiders. Using high-speed videography, we describe their numerous gaits, some analogous to those of their terrestrial counterparts, others specialized for life at the interface. The critical role of the rough surface of these water walkers in both floatation and propulsion is demonstrated. Their waxy, hairy surface ensures that their legs remain in a water-repellent state, that the bulk of their leg is not wetted, but rather contact with the water arises exclusively through individual hairs. Maintaining this water-repellent state requires that the speed of their driving legs does not exceed a critical wetting speed. Flow visualization reveals that the wakes of most water walkers are characterized by a series of coherent subsurface vortices shed by the driving stroke. A theoretical framework is developed in order to describe the propulsion in terms of the transfer of forces and momentum between the creature and its environment. The application of the conservation of momentum to biolocomotion at the interface confirms that the propulsion of water walkers may be rationalized in terms of the subsurface flows generated by their driving stroke. The two principal modes of propulsion available to small water walkers are elucidated. At driving leg speeds in excess of the capillary wave speed, macroscopic curvature forces are generated by deforming the meniscus, and the surface behaves effectively as a trampoline. For slower speeds, the driving legs need not substantially deform the surface but may instead simply brush it: the resulting contact or viscous forces acting on the leg hairs crossing the interface serve to propel the creature forward.

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Section: Discussionmentioning

confidence: 99%

The hydrodynamics of water-walking arthropods

2010

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“…According to Hu et al [42], water striders use their superhydrophobic legs to generate hemispherical vortices, which transfer sufficient momentum beneath the water surface to develop the hydrodynamic force necessary to propel the insect, similar to using oars to move a boat. Several water-walking machines are inspired by water striders and other insects [43]. Such devices are designed and constructed to precisely mimic the natural locomotion mechanisms of the insects.…”

Section: Water Stridersmentioning

confidence: 99%

Polymeric Slippery Coatings: Nature and Applications

Samaha¹,

Gad-el-Hak²

2014

Polymers

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Abstract:We review recent developments in nature-inspired superhydrophobic and omniphobic surfaces. Water droplets beading on a surface at significantly high static contact angles and low contact-angle hystereses characterize superhydrophobicity. Microscopically, rough hydrophobic surfaces could entrap air in their pores resulting in a portion of a submerged surface with air-water interface, which is responsible for the slip effect. Suberhydrophobicity enhances the mobility of droplets on lotus leaves for self-cleaning purposes, so-called lotus effect. Amongst other applications, superhydrophobicity could be used to design slippery surfaces with minimal skin-friction drag for energy conservation. Another kind of slippery coatings is the recently invented slippery liquid-infused porous surfaces (SLIPS), which are one type of omniphobic surfaces. Certain plants such as the carnivorous Nepenthes pitcher inspired SLIPS. Their interior surfaces have microstructural roughness, which can lock in place an infused lubricating liquid. The lubricant is then utilized as a repellent surface for other liquids such as water, blood, crude oil, and alcohol. In this review, we discuss the concepts of both lotus effect and Nepenthes slippery mechanism. We then present a review of recent advances in manufacturing polymeric and non-polymeric slippery surfaces with ordered and disordered micro/nanostructures. Furthermore, we discuss the performance and longevity of such surfaces. Techniques used to characterize the surfaces are also detailed. We conclude the article with an overview of the latest advances in characterizing and using slippery surfaces for different applications.

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“…Although denser than water, they rely upon surface tension forces in the manner of water-walking insects and certain biomimetic robots (15)(16)(17). However, surface tension is generally too weak to support objects that have the density of water and a size much larger than the capillary length ℓ c ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi σ w ∕ðρ w gÞ p ≈ 2.3 mm, where σ w is the surface tension of water.…”

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confidence: 99%

Fire ants self-assemble into waterproof rafts to survive floods

Mlot

Tovey²,

Hu³

2011

Proc. Natl. Acad. Sci. U.S.A.

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198

197

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Why does a single fire ant Solenopsis invicta struggle in water, whereas a group can float effortlessly for days? We use time-lapse photography to investigate how fire ants S. invicta link their bodies together to build waterproof rafts. Although water repellency in nature has been previously viewed as a static material property of plant leaves and insect cuticles, we here demonstrate a selfassembled hydrophobic surface. We find that ants can considerably enhance their water repellency by linking their bodies together, a process analogous to the weaving of a waterproof fabric. We present a model for the rate of raft construction based on observations of ant trajectories atop the raft. Central to the construction process is the trapping of ants at the raft edge by their neighbors, suggesting that some "cooperative" behaviors may rely upon coercion.cooperative animal behavior | surface tension | adhesive | emergent | differential equation

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Water-walking devices

Cited by 20 publications

References 29 publications

The hydrodynamics of water-walking arthropods

The hydrodynamics of water-walking arthropods

Polymeric Slippery Coatings: Nature and Applications

Fire ants self-assemble into waterproof rafts to survive floods

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