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E u r o S c i C o n C o n f e r e n c e o n
Nanotechnology &
Smart Materials
Nano Research & Applications
ISSN 2471-9838
O c t o b e r 0 4 - 0 6 , 2 0 1 8
Am s t e r d a m , N e t h e r l a n d s
Nanotechnology & Smart Materials 2018
Page 20
N
ature has always been our inspiration source of innovations. Chinese Kung Fu developed
effective moves from hunting skills of powerful beasts like snakes, eagles, and tigers; airplanes mimic the skillful flight of birds;
legged robots imitate legged animals such as dogs and spiders. Nowadays, state-of-the-art technology enables us to unveil mysteries
of themicroscopicworld and thus invent at microscalewith precision. We have been using the precision ofmicrofluidics inmanipulating
liquids at nano-/subnano-liters and engineering nano-/micro- structures to mimic evolutionarily-optimized nano/microstructures in
insects that interact with liquids, and thus developed a series of techniques for manipulating liquids precisely: water collecting, liquids
repelling, and droplets manoeuvring. The breakthroughs have yielded three articles in Nature Communications. Unique structural and
topological features of spider-silks and their web enable them being a super water collector witnessed by a large number of water
droplets handing on them in the early morning. With the microfluidic technology, we have precisely fabricated robust microfibers
with spindle cavity-knots and different topological fiber-networks in mimicking these features. These microfibers are endowed with
unique surface roughness, mechanical strength, and long-term durability, thus enabling a super performance in collecting water. The
maximumwater volume collected on a single knot is almost 495 times the knot volume; the water collection is even more efficient and
scalable with their networks. These light-weighted yet tough, low-cost microfibers offer promising opportunities for large-scale water
collection in water-deficient areas. Liquid-repellent surfaces repel liquids instead of allowing droplets to adhere. These surfaces are
important in many fields including self-cleaning clothes and kitchenware, enhanced heat transfer, and anti-fouling, anti-corrosive and
drag reduction coatings. The dream of research and development on liquid-repellents is a structure that has robust liquid repellency,
strong mechanical stability, and is inexpensive to produce on a commercial scale. However, the functional outcomes of existing liquid-
repellent surfaces have not been satisfactory, because of inadequacies of conventional structural design and fabrication approaches
in engineering microstructures and properties of such surfaces. We developed a low-cost scalable approach for the fabrication of
well-defined porous surfaces with robust liquid repellency and strong mechanical stability. The design of the liquid-repellent surfaces
is inspired by structures on springtail cuticles, which can effectively resolve the longstanding conflict between the liquid repellency and
the mechanical stability. Springtails are soil-dwelling arthropods whose habitats often experience rain and flooding. As a consequence,
springtails have evolved cuticleswith strongmechanical durability and robust liquid repellency to resist friction fromsoil particles and to
survive in watery environments. We design the porous surfaces to be composed of interconnected honeycomb-like microcavities with
a re-entrant profile: the interconnectivity ensures mechanical stability and the re-entrant structure yields robust liquid repellency. The
cuticle-like porous surfaces are fabricated by self-assembly using microfluidic droplets, which takes full advantage of the capabilities
of microfluidics in terms of scalability and precise-handling of small fluid volumes. The generation of these cuticle-like porous surfaces
usingmicrofluidics has led to precise, controllable, scalable, and inexpensive fabrication. Some semiaquatic insects can readily walk on
water and climb up menisci slope due to the dense hair mat and retractable claws of complementary wettability on their tarsi. Inspired
by this, we created a mechano-regulated surface whose adhesive force to liquid droplets can be simply switched through mechanical
regulation. The mechano-regulated surface functions as a “magic hand” that can capture and release multiple tiny droplets precisely in
a loss-freemanner, and works for both water and oil droplets down to nano-litre scale. These surfaces are relevant and crucial in various
high-precision fields such asmedical diagnosis and drug discovery where the precise transferring of tiny liquid is amust. Learning from
nature paves the way for creating nano/microstructures with unique features to interact with liquids on-demand. Small yet powerful,
these structures can manipulate liquids effectively and precisely. With these techniques, water may be gathered directly from the air in
deserts, no more laundry may become true, and liquids can be conveniently handled like solids
Microfluidics enabled structures for
manipulating liquids
Liqiu Wang
The University of Hong Kong, Hong Kong
HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), China
Liqiu Wang, Nano Res Appl Volume:4
DOI: 10.21767/2471-9838-C6-023