The ability to control drops and their movements on phobic surfaces is important in printing or patterning, microfluidic devices, and water-repellent materials. These materials are always micro-/nanotextured, and a natural limitation of repellency occurs when drops are small enough (as in a dew) to get trapped in the texture. This leads to sticky Wenzel states and destroys the superhydrophobicity of the material. Here, we show that droplets of volume ranging from femtoliter (fL) to microliter (μL) can be self-removed from the legs of water striders. These legs consist of arrays of inclined tapered setae decorated by quasi-helical nanogrooves. The different characteristics of this unique texture are successively exploited as water condenses, starting from selfpenetration and sweeping effect along individual cones, to elastic expulsion between flexible setae, followed by removal at the anisotropic leg surface. We envision that this antifogging effect at a very small scale could inspire the design of novel applicable robust water-repellent materials for many practical applications.water strider | water repellency | self-propulsion | antifogging | breath figure W hen a vapor condenses on a rough hydrophobic surface, liquid nuclei naturally appear within the roughness, forming tiny droplets stuck in the texture (1-3). Without the assistance of external forces, dew tightly adheres to the surface in the so-called Wenzel state, which most often destroys the superhydrophobicity of the material (4, 5). An applicable robust water-repellent surface thus requires an additional mechanism to expel these condensates from the texture (6). It has been reported in the literature that nanotextures (such as found on the surface of lotus leaves or cicada wings) might generate adhesion forces small enough to permit an efficient conversion of surface energy (coming from droplet coalescence) into kinetic energy, so that droplets can be mobilized (7-9). However, contact angle hysteresis effects are generally dominant at a small scale, so that a key challenge for antifogging materials lies in the generation of a force able to expel droplets from microtextures.Water striders (Gerris remigis, Fig. 1A) living at the water surface in a highly humid environment offer a remarkably simple solution to this problem. Without any external force, tiny condensed droplets in the range of femtoliters (fL) to microliters (μL) get removed from striders' legs, owing to the presence of oriented conical setae. A Gerris leg is a centimeter-size cylinder (of typical diameter 150 μm) decorated by an array of inclined tapered hairs characterized in Fig. 1 B and C by micro X-ray computed tomography (XCT) and scanning electron microscopy (SEM). Individual setae have a length L = 40-50 μm, a maximum diameter of ∼3 μm, and an apex angle of ∼5°. They make regular arrays with a mutual distance of 5-10 μm, and are tilted by an angle β = 25-35°to the base of the leg (Fig.

The controllable liquid transfer of a Chinese brush is attributable to the unique anisotropic multi-scale structures of the freshly emergent hairs. A large mass of liquid an be dynamically balanced within the brush as a cooperative effect of the Laplace pressure difference, the asymmetrical retention force, and gravity. Inspired by this, a device is developed with parallel hairs that allows for direct writing of micro-lines.

By rationally designing superhydrophobic electrodes with different underwater wetting states, it is revealed that only the underwater Wenzel-Cassie coexistent state shows the clearly enhanced ability in catalyzing the oxygen reduction reaction, a typical underwater gas-consuming reaction at electrode. It is proposed that the maximizing and stabilizing the liquid/gas/solid triphase interface, endowed by the underwater Wenzel-Cassie coexistent state, plays a rather crucial role.

Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well-controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self-assembly of conjugated backbones to proceed in a quasi-steady state via a certain direction, which is attributed to the controllable receding of the three-phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as-prepared polymer thin films exhibit over six times higher charge-carrier mobility compared to the spin-coated films, which therefore provides a general approach for high-performance organic thin-film transistors.

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