Architecture-Driven Fast Droplet Transport without Mass Loss

Abstract

Spontaneous droplet transport without mass loss has great potential applications in the fields of energy and biotechnology, but it remains challenging due to the difficulty in obtaining a sufficient driving force for the transport while suppressing droplet mass loss. Learning from the slippery peristome of Nepenthes alata and wedge topology of a shorebird beak that can spontaneously feed water against gravity, a combined system consisting of two face-to-face hydrophilic slippery liquid-infused porous surfaces (SLIPS) with variable beak-like opening and spacing was proposed to constrain the droplet inbetween and initiate fast droplet transport over a long distance of 75 mm with a maximum speed of 12.2 mm•s −1 without mass loss by taking advantage of the Laplace pressure gradient induced by the asymmetric shape of the constrained droplet. The theoretical model based on the Navier−Stokes equation was developed to interpret the corresponding mechanism of the droplet transport process. In addition, in situ sophisticated droplet manipulations such as droplet mixing are readily feasible when applying flexible 304 stainless foil as the substrate of SLIPS. It is believed that extended research would contribute to new references for the precise and fast droplet motion control intended for energy harvest and water collection devices.

Bionic surface diode for droplet steering

“…A slippery lubricant‐infused porous surface (SLIPS) inspired by Nepenthes alata plants has been widely applied for droplet motion control due to its intrinsic properties of ultralow contact angle hysteresis, self‐healing, pressure stability, and being immiscible with manipulated droplets 37–44 . The SLIPS patterns show strong affinity toward the deposited droplet but exhibit ultralow sliding resistance without absorption due to the immiscible droplet–lubricant interface, which is similar to the hydrophilic patterns from the aspect of stress condition but has no risk of mass loss 45–47 .…”

On-Chip Liquid Manipulation via a Flexible Dual-Layered Channel Possessing Hydrophilic/Hydrophobic Dichotomy

“…Fluid delivery is an eternal topic for both scientific research and industrial process, which determines mass transfer, multiphase exchange, chemical reaction, etc. − On-surface liquid manipulation can significantly diversify the transporting process and lower the energy consumption, which is ubiquitous in the natural world. − After thousands of years of evolution, animals and plants have evolved unique properties to realize highly efficient liquid utilization. − The oriented scales on lizard skin, the aligned ratchet on butterfly wings, and the geometric gradient of cactus spine and shorebird beak − can spontaneously control the directional liquid delivery on the basis of the asymmetric microstructure. Another strategy for regulating the liquid behavior is to use wettability contrast.…”

Sequence liquid manipulation on a multifunctional snowflake-patterned interface with dual unidirectional wettability

“…[30][31][32] Water-birds can deliver prey-lled water by opening and closing their beaks, directing droplets to their mouths. 33 Inspired by these biologically selfdriving methods, which mainly realize the directional transport of liquid droplets through an energy gradient generated by structure geometric anisotropy and materials wettability anisotropy, a large number of biomimetic droplet self-driven functional structures have been reported recently. Beneting from the asymmetric mechanism of water-birds to transport droplets, Dai et al created a hydrophobic/superhydrophilic Janus polyester/nitrocellulose textile with asymmetric hydrophilic conical micropores that can pump excess sweat from the hydrophobic layer to the super-hydrophilic layer directionally.…”