Through 3.7 billion years of evolution and natural selection, plants and animals in nature have ingeniously fulfilled a broad range of fascinating functions to achieve optimized performance in responding and adapting to changes in the process of interacting with complex natural environments. It is clear that the hierarchically organized micro/nanostructures of the surfaces of living organisms decisively manage fascinating and amazing functions, regardless of the chemical components of their building blocks. This conclusion now allows us to elucidate the underlying mechanisms whereby these hierarchical structures have a great impact on the properties of the bulk material. In this review, we mainly focus on advances over the last three years in bioinspired multiscale functional materials with specific wettability. Starting from selected naturally occurring surfaces, manmade bioinspired surfaces with specific wettability are introduced, with an emphasis on the cooperation between structural characteristics and macroscopic properties, including lotus leaf-inspired superhydrophobic surfaces, fish scale-inspired superhydrophilic/underwater superoleophobic surfaces, springtail-inspired superoleophobic surfaces, and Nepenthes (pitcher plant)-inspired slippery liquid-infused porous surfaces (SLIPSs), as well as other multifunctional surfaces that combine specific wettability with mechanical properties, optical properties and the unidirectional transport of liquid droplets. Afterwards, various top-down and bottom-up fabrication techniques are presented, as well as emerging cutting-edge applications. Finally, our personal perspectives and conclusions with regard to the transfer of micro- and nanostructures to engineered materials are provided.

Recent advances of bioinspired functional materials with specific wettability: from nature and beyond nature

Controlling dropwise condensation is fundamental to water-harvesting systems, desalination, thermal power generation, air conditioning, distillation towers, and numerous other applications. For any of these, it is essential to design surfaces that enable droplets to grow rapidly and to be shed as quickly as possible. However, approaches based on microscale, nanoscale or molecular-scale textures suffer from intrinsic trade-offs that make it difficult to optimize both growth and transport at once. Here we present a conceptually different design approach—based on principles derived from Namib desert beetles, cacti, and pitcher plants—that synergistically combines these aspects of condensation and substantially outperforms other synthetic surfaces. Inspired by an unconventional interpretation of the role of the beetle’s bumpy surface geometry in promoting condensation, and using theoretical modelling, we show how to maximize vapour diffusion fluxat the apex of convex millimetric bumps by optimizing the radius of curvature and cross-sectional shape. Integrating this apex geometry with a widening slope, analogous to cactus spines, directly couples facilitated droplet growth with fast directional transport, by creating a free-energy profile that drives the droplet down the slope before its growth rate can decrease. This coupling is further enhanced by a slippery, pitcher-plant-inspired nanocoating that facilitates feedback between coalescence-driven growth and capillary-driven motion on the way down. Bumps that are rationally designed to integrate these mechanisms are able to grow and transport large droplets even against gravity and overcome the effect of an unfavourable temperature gradient. We further observe an unprecedented sixfold-higher exponent of growth rate, faster onset, higher steady-state turnover rate, and a greater volume of water collected compared to other surfaces. We envision that this fundamental understanding and rational design strategy can be applied to a wide range of water-harvesting and phase-change heat-transfer applications.

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Condensation on Slippery Asymmetric Bumps

External Stimuli Responsive Liquid‐Infused Surfaces Switching between Slippery and Nonslippery States: Fabrications and Applications

Biological and bioinspired materials: Structure leading to functional and mechanical performance.

In recent years, water harvesting in arid or semi-arid areas has gained increasing attention. Inspired by the fog harvesting ability of hydrophobic–hydrophilic surfaces associated with Namib desert beetles, considerable effort has been expended in creating such bionic surfaces. However, designing a surface with excellent water harvesting, superamphiphobic, and water/oil self-cleaning properties remains challenging. Herein, an innovative hybrid consisting of a superamphiphobic surface combined with hydrophilic/hydrophobic particles is fabricated by a facile method. This hybrid surface exhibits a praiseworthy drop nucleation effect, high removal efficiency, excellent water collection efficiency, and commendable water/oil self-cleaning performance. The surface’s water/oil wettability, condensation properties, water collection rate and its dependence on the relative humidity and fog flow velocity were systematically investigated. The results obtained strongly indicated that the proposed hybrid superamphiphobic surface exhibits enhanced water drop condensation and water collection performance. In fact, the hybrid superamphiphobic surface doped with silicon carbide particles wrapped with an acrylic acid polymer emulsion (SiC@PAA) exhibited a better water harvesting effect, with a water collection rate more than double that of the nano-SiO2 superamphiphobic surface. The findings of this work are considered instrumental to the further design and implementation of hybrid superamphiphobic surfaces for cost-efficient atmospheric water harvesting.

Superamphiphobic coatings with polymer-wrapped particles: enhancing water harvesting

Namib Desert beetles harvest water from harsh environments by using their hydrophilic-hydrophobic dorsal surfaces. Generally, Cassie-state superhydrophobic materials are chosen as substrates to prepare bioinspired (super)hydrophilic/(super)hydrophobic patterned surfaces. However, due to the low adhesion and strong repellency, aqueous solution cannot be directly set on Cassie superhydrophobic materials until the dropping volume is larger than 6.5 μL. Therefore, arranging a (super)hydrophilic substance on Cassie superhydrophobic substrates to construct (super)hydrophilic/superhydrophobic patterned surfaces still remains a challenge. In this work, by prewetting with dichloromethane (DCM), the mussel-inspired hydrophilic and bio-adhesive dopamine solution (DA) could be dripped onto a Cassie superhydrophobic Cu surface with an ultralow volume of 0.1 μL, whereby low surface tension DCM would "cloak" the high surface tension DA. Along with DCM volatility, DA was adhered on the Cassie superhydrophobic surface and would then self-polymerize into hydrophilic polydopamine domains, thus hydrophilic/superhydrophobic patterned surfaces with efficient water collection could be successfully developed inspired by Namib Desert beetles and mussels. The bioinspired materials show the potential for real-world industrialization in a large scale, which is of great significance for providing living security for those living in areas with no access to fresh water.

Prewetting dichloromethane induced aqueous solution adhered on Cassie superhydrophobic substrates to fabricate efficient fog-harvesting materials inspired by Namib Desert beetles and mussels.

Ruilin Duan

Papers

Prewetting dichloromethane induced aqueous solution adhered on Cassie superhydrophobic substrates to fabricate efficient fog-harvesting materials inspired by Namib Desert beetles and mussels.