Fluid manipulation via multifunctional lubricant infused slippery surfaces: principle, design and applications.

Water-repellent interfaces with high performance have emerged as an indispensable platform for developing advanced materials and devices. Inspired by the pitcher plant, slippery liquid-infused porous surfaces (SLIPSs) with reliable hydrophobicity have proven to possess great potential for various applications in droplet and bubble manipulation, droplet energy harvesting, condensation, fog collection, anti-icing, and anti-biofouling due to their excellent properties such as persistent surface hydrophobicity, molecular smoothness, and fluidity. This review aims to introduce the development history of interaction between SLIPSs and fluids as well as the design principles, preparation methods, and various applications of some of the more typical SLIPSs. The fluid manipulation strategies of the slippery surfaces have been proposed including the wettability pattern, oriented micro-structure, and geometric gradient. At last, the application prospects of SLIPSs in various fields and the challenges in the design and fabrication of slippery surfaces are analyzed. We envision that this review can provide an overview of the fluid manipulating processes on slippery surfaces for researchers in both academic and industrial fields.

Designing Flexible but Tough Slippery Track for Underwater Gas Manipulation.

Lubricant-infused slippery surface exhibits a series of superior properties such as pressure tolerance, self-healing, oil-repellence, etc. Especially when being applied in an aqueous environment, the reliable bubble manipulating ability of slippery surface offers great opportunities to develop advanced systems in the field of gas transport, water splitting, etc. To improve the strength and the functionality of slippery surfaces, a sliced lubricant-infused slippery (SLIS) track is presented here, possessing both flexibility and toughness for underwater bubble manipulation. The rigid slippery slices with hydrophobic porous structure are linked by the liquid bridge of silicone oil, resulting in a continuous lubricant layer for bubble transfer. Taking advantage of this unique assembled structure, the in situ bubble controlling process, that is, pinning and moving, is achieved via the stretching/releasing of an elastic SLIS track. Besides, on the basis of the integrated design, a hypothesis of underwater gas mining is proved in the all-in-one process including the micro-bubble generation, bubble collection, and gas transport. The current design paves an avenue to reinforce the structure of slippery surfaces, and should promote the function of underwater bubble manipulation toward real-world applications.

Hydrophobic/Hydrophilic Cooperative Janus System for Enhancement of Fog Collection.

Harvesting micro-droplets from fog is a promising method for solving global freshwater crisis. Different types of fog collectors have been extensively reported during the last decade. The improvement of fog collection can be attributed to the immediate transportation of harvested water, the effective regeneration of the fog gathering surface, etc. Through learning from the nature's strategy for water preservation, the hydrophobic/hydrophilic cooperative Janus system that achieved reinforced fog collection ability is reported here. Directional delivery of the surface water, decreased re-evaporation rate of the harvested water, and thinner boundary layer of the collecting surface contribute to the enhancement of collection efficiency. Further designed cylinder Janus collector can facilely achieve a continuous process of efficient collection, directional transportation, and spontaneous preservation of fog water. This Janus fog harvesting system should improve the understanding of micro-droplet collection system and offer ideas to solve water resource crisis.

Direct insight into the three-dimensional internal morphology of solid-liquid-vapor interfaces at microscale.

Solid-liquid-vapor interfaces dominated by the three-phase contact line, usually performing as the active center in reactions, are important in biological and industrial processes. In this contribution, we provide direct three-dimensional (3D) experimental evidence for the inside morphology of interfaces with either Cassie or Wenzel states at micron level using X-ray micro-computed tomography, which allows us to accurately "see inside" the morphological structures and quantitatively visualize their internal 3D fine structures and phases in intact samples. Furthermore, the in-depth measurements revealed that the liquid randomly and partly located on the top of protrusions on the natural and artificial superhydrophobic surfaces in Cassie regime, resulting from thermodynamically optimal minimization of the surface energy. These new findings are useful for the optimization of classical wetting theories and models, which should promote the surface scientific and technological developments.

Bioinspired Gas Manipulation for Regulating Multiphase Interactions in Electrochemistry.

The manipulation of gas in multiphase interactions plays a crucial role in various electrochemical processes. Inspired by nature, researchers have explored bioinspired strategies for regulating these interactions, leading to remarkable advancements in design, mechanism, and applications. This paper provides a comprehensive overview of bioinspired gas manipulation in electrochemistry. It traces the evolution of gas manipulation in gas-involving electrochemical reactions, highlighting the key milestones and breakthroughs achieved thus far. The paper then delves into the design principles and underlying mechanisms of superaerophobic and (super)aerophilic electrodes, as well as asymmetric electrodes. Furthermore, the applications of bioinspired gas manipulation in hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), and other gas-involving electrochemical reactions are summarized. The promising prospects and future directions in advancing multiphase interactions through gas manipulation are also discussed.

Advances in Bioinspired Superhydrophobic Surfaces Made from Silicones: Fabrication and Application.

As research on superhydrophobic materials inspired by the self-cleaning and water-repellent properties of plants and animals in nature continues, the superhydrophobic preparation methods and the applications of superhydrophobic surfaces are widely reported. Silicones are preferred for the preparation of superhydrophobic materials because of their inherent hydrophobicity and strong processing ability. In the preparation of superhydrophobic materials, silicones can both form micro-/nano-structures with dehydration condensation and reduce the surface energy of the material surface because of their intrinsic hydrophobicity. The superhydrophobic layers of silicone substrates are characterized by simple and fast reactions, high-temperature resistance, UV resistance, and anti-aging. Although silicone superhydrophobic materials have the disadvantages of relatively low mechanical stability, this can be improved by the rational design of the material structure. Herein, we summarize the superhydrophobic surfaces made from silicone substrates, including the cross-linking processes of silicones through dehydration condensation and hydrosilation, and the surface hydrophobic modification by grafting hydrophobic silicones. The applications of silicone-based superhydrophobic surfaces have been introduced such as self-cleaning, corrosion resistance, oil-water separation, etc. This review article should provide an overview to the bioinspired superhydrophobic surfaces of silicone-based materials, and serve as inspiration for the development of polymer interfaces and colloid science.

On-Chip Liquid Manipulation via a Flexible Dual-Layered Channel Possessing Hydrophilic/Hydrophobic Dichotomy.

The hydrophilic/hydrophobic cooperative interface provides a smart platform to control liquid distribution and delivery. Through the fusion of flexibility and complex structure, we present a manipulable, open, and dual-layered liquid channel (MODLC) for on-demand mechanical control of fluid delivery. Driven by anisotropic Laplace pressure, the mechano-controllable asymmetric channel of MODLC can propel the directional slipping of liquid located between the paired tracks. Upon a single press, the longest transport distance can reach 10 cm with an average speed of ∼3 cm/s. The liquid on the MODLC can be immediately manipulated by pressing or dragging processes, and versatile liquid-manipulating processes on hierarchical MODLC chips have been achieved, including remote droplet magneto-control, continuous liquid distributor, and gas-producing chip. The flexible hydrophilic/hydrophobic interface and its assembly can extend the function and applications of the wettability-patterned interface, which should update our understanding of complex systems for sophisticated liquid transport.

Designing a slippery/superaerophobic hierarchical open channel for reliable and versatile underwater gas delivery.

Achieving long-term and stable gas manipulation in an aqueous environment is necessary to improve multiphase systems relating to gas/liquid interaction. Inspired by the Pitcher plant and the hummingbird beak, we report a slippery/superaerophobic (SLSO) hierarchical fluid channel for continuous, durable, and flexible gas transport. The immiscible lubricant layer inside the SLSO channel promotes one-year stability of gas transport, and the maximum flux of this open channel can reach 3000 mL h-1. Further integration of a CO2 capturing microchip demonstrates the availability and potential of this gas-manipulating interface, which should provide a valuable platform to develop advanced materials and devices.

Improved Liquid Collection on a Dual-Asymmetric Superhydrophilic Origami.

Manipulating fluid with an open channel provides a promising strategy to simplify the current systems. Nevertheless, spontaneous on-surface fluid transport with large flux, high speed, and long distance remains challenging. Inspired by scallop shells, here a shell-like superhydrophilic origami (S-SLO) with multiple-paratactic and dual-asymmetric channels is presented to improve fluid collection. The origami channel can capture various types of liquids, including droplets, flow, and steam, and then transport collected liquid unidirectionally. The S-SLO with 2 mm depth can reach maximum flux of 450 mL h-1 , which is five times the capacity of a flat patterned surface with similar dimension. To diversify the function of such interface, the SLO is further integrated with a superhydrophobic zirconium carbide/silicone coating for enhanced condensation via the collaboration of directional fluid manipulation and a radiative cooling layer. Compared with the unmodified parallel origami, the shell-like origami with a radiative cooling layer shows a 56% improvement in condensate efficiency as well as the directional liquid drainage. This work demonstrates a more accessible design for the optimization of on-surface fluid control, and the improved performance of liquid transport should extend the applications of bioinspired fluid-manipulating interfaces.

Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene.

The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m-2·h-1 with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application.

Unidirectional Moisture Delivery via a Janus Photothermal Interface for Indoor Dehumidification: A Smart Roof.

Rational control of the humidity in specific environments plays an important role in green building, equipment protection, etc. A smart apparatus that can actively expel inner moisture and largely prevent outer liquid penetration can be highly desirable. Through the integration of the Janus interface with unidirectional liquid manipulation and the solar evaporating layer, here, a Janus solar dehumidifying interface (JSDI) is designed for the switchable moisture management of an indoor environment. By covering with the JSDI roof, the continuous elimination of inner water is achieved via outward condensate delivery and solar evaporation on sunny days. On rainy days, JSDI with a hydrophobic lower surface can largely hamper inward liquid leakage and then spontaneously drain the accumulated water via a siphoning structure. The real-world water evaporation rate via the JSDI is ≈0.38 kg m-2 h-1 on an autumn day, showing a promising function of in situ moisture expelling. In addition, the JSDI is made of natural materials that are easy to scale up with a cost of four dollars per square meter. It is envisioned that the JSDI may meet the wide requirements of indoor dehumidification and update the understanding of the integration of Janus interfaces and solar steam generation.

Spontaneous Separation of Immiscible Organic Droplets on Asymmetric Wedge Channels with Hierarchical Microchannels.

Spontaneous separation of immiscible organic droplets has substantial research implications for environmental protection and resource regeneration. Compared to the widely explored separation of oil-water mixtures, there are fewer reports on separating mixed organic droplets on open surfaces due to the low surface tension differences. Efficient separation of mixed organic liquids by exploiting the rapid spontaneous transport of droplets on open surfaces remains a challenge. Here, through the fusion of inspiration from the fast droplet transport capability of Sarracenia trichome and the asymmetric wedge channel structure of shorebird beaks, this work proposes a spine with hierarchical microchannels and wedge channels (SHMW). Due to the synergistic effect of capillary force and asymmetric Laplace force, the SHMW can rapidly separate mixed organic droplets into two pure phases without requiring additional energy. In particular, the self-spreading of the oil solution on the open channel surface is utilized to amplify the surface energy difference between two droplets, and SHMW achieves the pickup of oil droplets floating on the surface of the organic solution. The maximum separation efficiency on 3-SHMW can reach 99.63%, and it can also realize the antigravity separation of mixed organic droplets with a surface tension difference as low as 0.87 mN·m-1. Furthermore, SHMW performs controllable separation, oil droplet pickup, and continuous separation and collection of mixed organic droplets. It is expected that this cooperative structure composed of hierarchical microchannels and wedge channels will be realized in resource recovery or chemical reactions in industrial production processes.

An interfacial floating tumbler with a penetrable structure and Janus wettability inspired by Pistia stratiotes.

Designing advanced interfacial materials is decisive to the improvement of multiphase systems. Inspired by the superior floatability of Pistia stratiotes, here we present a superhydrophobic/hydrophilic 3D Janus floater with a water managing ability. Its self-regulated floatation mechanism, as well as its water removal logic, should provide insight into the development of multifunctional interfacial carriers in the fields of micro-devices, solar evaporation, etc.

Bioinspired Anisotropic Slippery Cilia for Stiffness-Controllable Bubble Transport.

Bubbles play a crucial role in multidisciplinary industrial applications, e.g., heat transfer and mass transfer. However, existing methods to manipulate bubbles still face many challenges, such as buoyancy inhibition, hydrostatic pressure, gas dissolving, easy deformability, and so on. To circumvent these constraints, here we develop a bioinspired anisotropic slippery cilia surface to achieve an elegant bubble transport by tuning its elastic modulus, which results from the different contacts of bubbles with cilia, i.e., soft cilia will be easily bent by the bubble motion, while hard cilia will pierce into the bubble, consequently leading to the asymmetric three-phase contact line and resistance force. Moreover, a real-time and arbitrarily directional bubble manipulation is also demonstrated by applying an external magnetic field, enabling the scalable operation of bubbles in a remote manner. Our work exhibits a strategy of regulating bubble behavior smartly, which will update a wide range of gas-related sciences or technologies including gas evolution reactions, heat transfer, microfluidics, and so on.

Self-Propelled and Electrobraking Synergetic Liquid Manipulator toward Microsampling and Bioanalysis.

Droplet manipulation is of paramount significance for microfluidics-based biochips, especially for bioanalytical chips. Despite great progresses made on droplet manipulation, the existing bioanalytical methods face challenges in terms of capturing minute doses toward hard-to-obtain samples and analyzing biological samples at low temperatures immediately. To circumvent these limitations, a self-propelled and electric stimuli synergetic droplet manipulator (SES-SDM) was developed by a femtosecond laser microfabrication strategy followed by post-treatment. Combining the inspiration from cactus and Nepenthes pitcher plants, the wedge structure with the microbowl array and silicone oil infusion was endowed cooperatively with the SES-SDM. With the synergy of the ultralow voltage (4.0 V) stimuli, these bioinspired features enable the SES-SDM to transport the droplet spontaneously and controllably, showing the maximum fast motion (15.7 mm/s) and long distance (96.2 mm). Remarkably, the SES-SDM can function at -5 °C without the freezing of the droplets, where the self-propelled motion and electric-responsive pinning can realize the accurate capture and real-time analysis of the microdroplets of the tested samples. More importantly, the SES-SDM can realize real-time diagnosis of excessive heavy metal in water by the cooperation of self-propulsion and electro-brake. This work opens an avenue to design a microsampling (5-20 µL) manipulator toward producing the minute samples for efficient bioanalysis and offers a strategy for microanalysis using the synergistic droplet manipulation.

A Multi-Bioinspired Dual-Gradient Electrode for Microbubble Manipulation toward Controllable Water Splitting.

Clean energy generated from total water splitting is expected to be an affordable, sustainable, and reliable resource but it remains a challenge to gain pure fuel with a controllable pathway. Here, a simple and economical strategy that enables in situ separation of H2 /O2 product by manipulating the generated gas phases with the aid of multi-bioinspired electrodes is proposed. This versatile electrode is based on a Janus asymmetric foam with dual gradients, i.e., the wettability gradient promotes the one-way gas penetration and the geometry gradient boosts the spontaneous on-surface transport in the horizontal direction, which cooperatively facilitates self-driven 3D bubble transport in an aqueous environment. Benefitting from the 3D bionic electrode, the limited distance between the cathode and the anode can be reduced to 1 mm, and the corresponding current density is enhanced 1.5 times as compared with the common condition. This Janus triangular electrode with dual directionality elucidates 3D smart bubble manipulation during overall water splitting and should offer a great opportunity to develop advanced electrochemical processes toward complicated environments such as confined space and zero gravity.

Random Organic Nanolaser Arrays for Cryptographic Primitives.

Next-generation high-security cryptography and communication call for nondeterministic generation and efficient authentication of unclonable bit sequences. Physical unclonable functions using inherent randomness in material and device fabrication process have emerged as promising candidates for realizing one-way cryptographic systems that avoid duplication and attacks. However, previous approaches suffer from the tradeoffs between low-efficiency fabrication and complicated authentication. Here, all-photonic cryptographic primitives by solution printing of organic nanolaser arrays with size-dependent dual lasing emission are reported. The stochastic distribution of organic solution into discrete capillary bridges, triggered by high-rate solvent evaporation, on a periodic topographical template yields organic single crystals with regulated position, alignment, and random size, which ensures high entropy. Stimulated emission from different vibrational sublevels and the intrinsic self-absorption effect permit size-dependent dual-wavelength lasing emission at wavelengths of 660 and/or 720 nm, which can be efficiently encoded into quaternary cryptographic keys with high reliability. High entropy, solution-processed programming and all-photonic authentication of random organic nanolaser arrays facilitate their cryptographic implementation in secure communication with high throughput, efficiency, and low cost.

Bioinspired Slippery Cone for Controllable Manipulation of Gas Bubbles in Low-Surface-Tension Environment.

Manipulating bubbles in surfactant solutions or oil mediums is of vital importance in daily life and industries concerned with cosmetics, food, fermentation, mineral flotation, etc. However, realizing controllable regulation of a bubble's behavior is quite challenging in a low-surface-tension aqueous environment, which is mainly attributed to the strong affinity of liquid molecules to a solid surface to prevent the efficient interaction of gas bubbles with the solid surface. To address these issues, herein, we have taken inspiration from cactus spines and pitcher plants to develop a slippery copper cone (SCC), which can facilely manipulate gas bubble in surfactant solutions (as low as ∼29.9 mN/m, 20 °C), e. g., directional and continuous transportation of gas bubbles. This intriguing capability mainly originates from the cooperation of the conical morphology engendering a Laplace pressure and the slippery surface with low friction force but high affinity to bubbles. In addition, the SCC also shows an elegant capability of transporting gas bubbles in various organic solvents, such as formamide (57.4 mN/m, 20 °C), glycol (46.5 mN/m, 20 °C), dibutyl phthalate (37.0 mN/m, 20 °C), and dimethylformamide (35.8 mN/m, 20 °C). Furthermore, the prepared SCC also demonstrated distinguished feasibility in antibuoyancy bubble delivery, efficient collection of acidic CO2 microbubbles, and the underwater reaction of hydrogen and oxygen, endowing it with promising applications in various complex low-surface-tension environments.