Jie Ju

A multi-structural and multi-functional integrated fog collection system in cactus

Multiple biological structures have demonstrated fog collection abilities, such as beetle backs with bumps and spider silks with periodic spindle-knots and joints. Many Cactaceae species live in arid environments and are extremely drought-tolerant. Here we report that one of the survival systems of the cactus Opuntia microdasys lies in its efficient fog collection system. This unique system is composed of well-distributed clusters of conical spines and trichomes on the cactus stem; each spine contains three integrated parts that have different roles in the fog collection process according to their surface structural features. The gradient of the Laplace pressure, the gradient of the surface-free energy and multi-function integration endow the cactus with an efficient fog collection system. Investigations of the structure–function relationship in this system may help us to design novel materials and devices to collect water from fog with high efficiencies.

Structured cone arrays for continuous and effective collection of micron-sized oil droplets from water

Environmental protection agencies and the petroleum industry require effective methods to separate micron-sized oil droplets from water. However, for most existing separation methods, phase separation occurs in the oil-water mixture. The remaining micron-scale oil droplets, which are not affected by phase separation, are difficult to handle with conventional methods on a large scale because of either a lack of separation ability or drawbacks in throughput capacity. Here we develop an oleophilic array of conical needle structures for the collection of micron-sized oil droplets, inspired by the collection of similar sized water droplets on conical cactus spines. Underwater, these structures mimic cacti and can capture micron-sized oil droplets and continuously transport them towards the base of the conical needles. Materials with this structure show obvious advantages in micron-sized oil collection with high continuity and high throughput.

Direction Controlled Driving of Tiny Water Drops on Bioinspired Artificial Spider Silks

www.MaterialsViews.com C O M M Direction Controlled Driving of Tiny Water Drops on Bioinspired Artifi cial Spider Silks U N IC A By Hao Bai , Xuelin Tian , Yongmei Zheng ,* Jie Ju , Yong Zhao , and Lei Jiang * IO N Directional driving of liquid drops is of signifi cant interest in many applications, such as microfl uidic devices, [ 1–6 ] fog harvesting, [ 7 ] fi ltration, [ 8 ] and condensers. [ 9 ] For this purpose, great progress has been made in driving drops larger than hundreds of micrometers [ 9–23 ] by introducing chemical, [ 1 , 10 , 12–15 , 23 ] thermal, [ 16–19 ] or shape [ 20–22 ] gradients on surfaces. However, driving micrometer-sized drops is much more diffi cult because they encounter a larger contact angle (CA) hysteresis effect. [ 7 , 24 ] In nature, the wetted silk of cribellate spider offers new insights into solving this problem by combining different gradients together. [ 7 ] Here, inspired by the spider silk, we fabricated a series of artifi cial spider silks with spindle-knots in which the chemical compositions and surface nanostructures were subtly designed. Our investigations demonstrated that tiny water drops (tens of picoliters) could be driven with controllable direction (“toward” or “away from” the knot) by optimizing the cooperation of curvature, chemical, and roughness gradients on the fi ber surfaces. The study will pave the way for designing smart materials and devices to drive tiny water drops in a controllable manner. When a nylon fi ber was immersed into polymer solution and drawn out horizontally, a string of polymer drops, which became spindle-knots after being dried, formed on the fi ber due to the Rayleigh instability [ 25 ] of the polymer solution. The surface energy of the spindle-knots was tailored by choosing different polymers including poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(vinylidene fl uoride) (PVDF), which have intrinsic water contact angles of 56.7 ° , 68.4 ° , 93.3 ° , and 92.7 ° , respectively (see Supporting Information, Figure S1). On the other hand, the surface roughness (porous nanostructures) of the spindle-knots was also designed through phase separation

Efficient Water Collection on Integrative Bioinspired Surfaces with Star-Shaped Wettability Patterns

Inspired by the water-collecting strategies of desert beetles and spider silk, a novel kind of surface with star-shaped wettablity patterns has been developed. By combining both wettability and shape gradients, the as-prepared surface has gained higher efficiency in water collection compared to circle-shaped wettability patterns and uniformly superhydrophilic or superhydrophobic surfaces.

Controlled Fabrication and Water Collection Ability of Bioinspired Artificial Spider Silks

Figure 1 . Optical images of BASs fabricated at different conditions by drawing the nylon fi bers out of the PMMA/DMF solution. The drawing out velocity is changed from 10, 50, 100, 150, to 200 mm/min, and the solution concentration is changed from 3%, 5%, 7%, 9%, to 11% (PMMA in weight). In the images in c), where the concentration or velocity is too low to form the cylindrical solution fi lm, no obvious spindle-knots are found on the fi bers. In the images in a), where the concentration is too high for the solution fi lm to break up into droplets before being dried, the periodicity of the knots is poor and the knots are always in the asymmetric shape. In the images in b), where both the solution concentration and drawing out velocity are optimized, spindle-knots with good periodicity are fabricated on the nylon fi bers. Collecting water from fog is a feasible route to solve the problem of water shortage, especially in dry and fog-laden areas. [ 1–7 ] In nature some creatures have developed the amazing ability to collect water owing to special microand nanostructures on their surfaces, such as desert beetles [ 8 ] and cribellate spiders. [ 9 ] The desert beetle’s back is patterned with hydrophobic and hydrophilic regions. Water droplets fi rst condense on the hydrophilic region and then roll off the back because of gravity. Some research has been carried out to mimic the beetle’s back by collecting water on bioinspired two-dimensional substrates with patterned wettability. [ 10–12 ]

Peanut leaf inspired multifunctional surfaces

Nature has long served as a source of inspiration for scientists and engineers to design and construct multifunctional artificial materials. The lotus and the peanut are two typical plants living in the aquatic and the arid (or semiarid) habitats, respectively, which have evolved different optimized solutions to survive. For the lotus leaf, an air layer is formed between its surface and water, exhibiting a discontinuous three-phase contact line, which resulted in the low adhesive superhydrophobic self-cleaning effect to avoid the leaf decomposition. In contrast to the lotus leaf, the peanut leaf shows high-adhesive superhydrophobicity, arising from the formation of the quasi-continuous and discontinuous three-phase contact line at the microscale and nanoscale, respectively, which provides a new avenue for the fabrication of high adhesive superhydrophobic materials. Further, this high adhesive and superhydrophobic peanut leaf is proved to be efficient in fog capture. Inspired by the peanut leaf, multifunctional surfaces with structural similarity to the natural peanut leaf are prepared, exhibiting simultaneous superhydrophobicity and high adhesion towards water.

Temperature‐Driven Switching of Water Adhesion on Organogel Surface

Temperature-driven switching of water adhesion is realized on a novel n-paraffinswollen organogel by thermally controlling the transition of air/liquid/solid (ALS/ALLS) systems via the phasechange process of n-paraffin. The thermal control of both the water-drop sliding motion and the switching of the optical transparency shows potential applications in scientific research and daily life.

Large‐Scale Fabrication of Bioinspired Fibers for Directional Water Collection

Spider-silk inspired functional fibers with periodic spindle-knots and the ability to collect water in a directional manner are fabricated on a large scale using a fluid coating method. The fabrication process is investigated in detail, considering factors like the fiber-drawing velocity, solution viscosity, and surface tension. These bioinspired fibers are inexpensive and durable, which makes it possible to collect water from fog in a similar manner to a spiders web.

Directional shedding-off of water on natural/bio-mimetic taper-ratchet array surfaces

Surfaces that control fluids are important in self-cleaning, liquid-transport and cell-directing. They are significantly observed on biological surfaces that control wettability and adhesion by means of micro-/nanostructures, and have aroused interest in foundational and biomimetic research. Here, we report a novel taper-ratchet array on ryegrass leaf. It integrates a gradient of retention at solid–liquid interfaces in contrasting directions to reversibly generate the release or the pinning of solid–liquid contact lines, and accordingly, achieves effective directional water shedding-off properties. By mimicking taper-ratchets from ryegrass leaf, the polymer surfaces are fabricated successfully. They display a robust property of directional water shedding-off. When external vibrations are executed on polymer surfaces, the drops achieve a unidirectional self-shedding along the oriented direction of tips of taper-ratchets, because asymmetric retention forces are formed in the contrasting oriented directions. This investigation will be helpful to design a novel fluid-controlling surface that can be extended to applications such as self-cleaning, liquid-transport and cell-directed projects.

Influence of cuticle nanostructuring on the wetting behaviour/states on cicada wings

The nanoscale protrusions of different morphologies on wing surfaces of four cicada species were examined under an environmental scanning electron microscope (ESEM). The water contact angles (CAs) of the wing surfaces were measured along with droplet adhesion values using a high-sensitivity microelectromechanical balance system. The water CA and adhesive force measurements obtained were found to relate to the nanostructuring differences of the four species. The adhesive forces in combination with the Cassie-Baxter and Wenzel approximations were used to predict wetting states of the insect wing cuticles. The more disordered and inhomogeneous surface of the species Leptopsalta bifuscata demonstrated a Wenzel type wetting state or an intermediate state of spreading and imbibition with a CA of 81.3° and high adhesive force of 149.5 µN. Three other species (Cryptotympana atrata, Meimuna opalifer and Aola bindusara) exhibited nanostructuring of the form of conically shaped protrusions, which were spherically capped. These surfaces presented a range of high adhesional values; however, the CAs were highly hydrophobic (C. atrata and A. bindusara) and in some cases close to superhydrophobic (M. opalifer). The wetting states of A. bindusara, C. atrata and M. opalifer (based on adhesion and CAs) are most likely represented by the transitional region between the Cassie-Baxter and Wenzel approximations to varying degrees.