61 research outputs found
Pancake bouncing on superhydrophobic surfaces
Engineering surfaces that promote rapid drop detachment is of importance to a
wide range of applications including anti-icing, dropwise condensation6, and
self-cleaning. Here we show how superhydrophobic surfaces patterned with
lattices of submillimetre-scale posts decorated with nano-textures can generate
a counter-intuitive bouncing regime: drops spread on impact and then leave the
surface in a flattened, pancake shape without retracting. This allows for a
four-fold reduction in contact time compared to conventional complete rebound.
We demonstrate that the pancake bouncing results from the rectification of
capillary energy stored in the penetrated liquid into upward motion adequate to
lift the drop. Moreover, the timescales for lateral drop spreading over the
surface and for vertical motion must be comparable. In particular, by designing
surfaces with tapered micro/nanotextures which behave as harmonic springs, the
timescales become independent of the impact velocity, allowing the occurrence
of pancake bouncing and rapid drop detachment over a wide range of impact
velocities.Comment: 11 pages, 4 figures, 31 references, + 5 pages of supplementary
informatio
Printing surface charge as a new paradigm to program droplet transport
Directed, long-range and self-propelled transport of droplets on solid
surfaces, especially on water repellent surfaces, is crucial for many
applications from water harvesting to bio-analytical devices. One appealing
strategy to achieve the preferential transport is to passively control the
surface wetting gradients, topological or chemical, to break the asymmetric
contact line and overcome the resistance force. Despite extensive progress, the
directional droplet transport is limited to small transport velocity and short
transport distance due to the fundamental trade-off: rapid transport of droplet
demands a large wetting gradient, whereas long-range transport necessitates a
relatively small wetting gradient. Here, we report a radically new strategy
that resolves the bottleneck through the creation of an unexplored gradient in
surface charge density (SCD). By leveraging on a facile droplet printing on
superamphiphobic surfaces as well as the fundamental understanding of the
mechanisms underpinning the creation of the preferential SCD, we demonstrate
the self-propulsion of droplets with a record-high velocity over an ultra-long
distance without the need for additional energy input. Such a Leidenfrost-like
droplet transport, manifested at ambient condition, is also genetic, which can
occur on a variety of substrates such as flexible and vertically placed
surfaces. Moreover, distinct from conventional physical and chemical gradients,
the new dimension of gradient in SCD can be programmed in a rewritable fashion.
We envision that our work enriches and extends our capability in the
manipulation of droplet transport and would find numerous potential
applications otherwise impossible.Comment: 11 pages, 4 figure
Bio-inspired water-driven electricity generators: From fundamental mechanisms to practical applications
Harvesting water energy in various forms of water motion, such as evaporation, raindrops, river flows, ocean waves, and other, is promising to relieve the global energy crisis and reach the aim of carbon neutrality. However, this highly decentralized and distributed water energy poses a challenge on conventional electromagnetic hydropower technologies that feature centralization and scalization. Recently, this problem has been gradually addressed by the emergence of a myriad of electricity generators that take inspiration from natural living organisms, which have the capability to efficiently process and manage water and energy for survival in the natural competition. Imitating the liquid–solid behaviors manifested in ubiquitous biological processes, these generators allow for the efficient energy conversion from water–solid interaction into the charge transfer or electrical output under natural driving, such as gravity and solar power. However, in spite of the rapid development of the field, a fundamental understanding of these generators and their ability to bridge the gap between the fundamentals and the practical applications remains elusive. In this review, we first introduce the latest progress in the fundamental understanding in bio-inspired electricity generators that allow for efficient harvesting water energy in various forms, ranging from water evaporation, droplet to wave or flow, and then summarize the development of the engineering design of the various bio-inspired electricity generator in the practical applications, including self-powered sensor and wearable electronics. Finally, the prospects and urgent problems, such as how to achieve large-scale electricity generation, are presented
Topological liquid diode
The last two decades have witnessed an explosion of interest in the field of droplet-based microfluidics for their multifarious applications. Despite rapid innovations in strategies to generate small-scale liquid transport on such devices, the speed of motion is usually slow, the transport distance is limited, and the flow direction is not well controlled because of unwanted pinning of contact lines by defects on the surface. Here we report a new method of microscopic liquid transportation based on a unique topological structure that breaks the contact line pinning through efficient conversion of excess surface energy to kinetic energy at the advancing edge of the droplet whilst simultaneously arresting the reverse motion of the droplet via strong pinning. What results is a novel topological fluid diode that allows for a rapid, directional, and long-distance transport of virtually any kind of liquid without the need for an external energy input
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