Femtosecond laser composite manufactured double-bionic micro-nano structure for efficient photothermal anti-icing/deicing.

The solar anti-icing/deicing (SADI) strategy represents an environmentally friendly approach for removing ice efficiently. However, the extensive use of photothermal materials could negatively impact financial performance. Therefore, enhancing light utilization efficiency, especially by optimizing the design of a structure with a low content of photothermal materials, has rapidly become a focal point of research. Drawing inspiration from the antireflective micro-nano structure of compound eyes and the thermal insulating hollow structure of polar bear hair, we proposed a new strategy to design a bionic micro-nano hollow film (MNHF). The MNHF was created using a composite manufacturing process that combines femtosecond laser ablation with template transfer techniques. Both theoretical simulations and empirical tests have confirmed that this structure significantly improves photothermal conversion efficiency and thermal radiation capability. Compared to plane film, the photothermal conversion efficiency of MNHF is increased by 45.85%. Under 1.5 sun, the equilibrium temperature of MNHF can reach 73.8 °C. Moreover, even after 10 icing-deicing cycles, MNHF maintains an ultra-low ice adhesion strength of 1.8 ± 0.3 kPa. Additionally, the exceptional mechanical stability, chemical resistance, and self-cleaning capabilities of the MNHF make its practical application feasible. This innovative structure paves the way for designing cost-effective and robust surfaces for efficient photothermal anti-icing/deicing on airplane wings.

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.

Flexible Tri-switchable Wettability Surface for Versatile Droplet Manipulations.

Smart surfaces with tunable wettability are promising due to their abilities to create diversified functionalities that the fixed surfaces cannot provide. However, limited by imprecise adjustment of structural geometry and almost conventional switching modes of wettability, it is still challenging to achieve the reversible switching between multiple wetting states. Herein, a novel tri-switchable wettability surface with an in situ switching ability is used for the manipulation of a given droplet, which consists of a stretchable substrate and a micron column array. The femtosecond laser direct writing technique is utilized to generate distinct wettability of the two components. Taking the advantage of good tensile properties, the surface morphology is adjusted in a rapid, reversible way to obtain diverse wetting performances from the lotus-like effect to rice-leaf-like anisotropy and then to the rose-petal-like effect. Based on the triplex wetting transition on the same surface, we further developed a multifunctional device to realize a range of in situ manipulations, including the surface self-cleaning, the directional transport of droplets, and the capture, the vertical transport, and release of droplets. This work paves the way for expanding the field of smart surfaces with tunable wettability beyond conventional dual-property wetting behavior and exhibits versatile manipulations of droplets for microfluidic applications.

Robust Underwater Air Layer Retention and Restoration on Salvinia-Inspired Self-Grown Heterogeneous Architectures.

Salvinia's long-term underwater air layer retention ability has inspired researchers to develop artificial microstructures. However, Salvinia has an exquisite combination of a complicated hollow structure and heterogeneous chemical properties, which makes artificial reproduction beyond the capabilities of traditional fabrication techniques. In addition, under extremely low underpressure conditions, the mechanism of retention and restoration of the underwater air layer of Salvinia remains unclear. Herein, by combining the shape memory polymer "top-constrained self-branching (TCSB)" and hydrophilic SiO2 microspheres trapping, four-branch hollow microstructures with heterogeneous chemical properties are fabricated. By applying underpressure, the crucial role of hydrophilic apexes is unveiled in air layer restoration. Through the calculation of the surface energy, the underlying mechanism is well interpreted. This study holds great promise for developing Salvinia-inspired artificial structures and reveals the underlying mechanism of the robust air retention and recovery capability of Salvinia leaves in extreme environments.

Femtosecond Laser Regulated Ultrafast Growth of Mushroom-Like Architecture for Oil Repellency and Manipulation.

Natural organisms can create various microstructures via a spontaneous growth mode. In contrast, artificial protruding microstructures are constructed by subtractive methods that waste materials and time or by additive methods that require additional materials. Here, we report a facile and straightforward strategy for a laser-induced self-growing mushroom-like microstructure on a flat surface. By simply controlling the localized femtosecond laser heating and ablation on the poly(ethylene terephthalate) tape/heat-shrinkable polystyrene bilayer surface, it is discovered that a mushroom-like architecture can spontaneously and rapidly grow out from the original surface within 0.36 s. The dimension of the re-entrant micropillar array (cap diameter, pillar spacing, and height) can be accurately controlled through the intentional control of laser scanning. Followed by a fluorination and spray coating, the obtained surface can realize the repellency and manipulation of oil droplets. This work provides new opportunities in the fields of microfabrication, microfluidics, microreactor engineering, and wearable antifouling electronics.

3D Multiscale Micro-/Nanofolds by Femtosecond Laser Intermittent Ablation and Constrained Heating on a Shape Memory Polymer.

Spontaneous wrinkling of films with a thickness gradient offers a new opportunity for constructing various 3D hierarchical surface morphologies. Unfortunately, accurately and facilely controlling the gradient film thickness to yield multiscale and 3D hierarchical micro-/nanostructures is still difficult. Here, a rapid, facile, and highly controllable fabricating strategy for realizing 3D multiscale hierarchical micro-/nanofolds on a shape memory polymer (SMP) surface is reported. First, the nanoparticle film with gradient thickness is rapidly (100 ms to 4 s) and facilely obtained by laser intermittent ablation on the SMP, termed as laser ablation-induced gradient thickness film. Following one-time constrained heating, the 3D micropillars grow out of the substrate based on the "self-growing effect," and the nanoparticle gradient film on its top shrinks into multiscale micro-/nanofolds simultaneously. Significantly, the evolution process and the underlying mechanism of the 3D micro-/nanofolds are systematically investigated. Fundamental basis enables us to accurately regulate the gradient thickness of nanoparticle films and feature size of folds by varying laser scanning times and scanning path. Finally, desirable patterns on micro-/nanofolds can be readily realized by programmable laser cleaning technology, and the tunable adhesion of the water droplet on the multiscale structured surface is demonstrated, which is promising for microdroplet manipulation.

Cross-Species Bioinspired Anisotropic Surfaces for Active Droplet Transportation Driven by Unidirectional Microcolumn Waves.

Natural evolution has endowed diverse species with distinct geometric micro/nanostructures exhibiting admirable functions. Examples include anisotropic microgrooves/microstripes on the rice leaf surface for passive liquid directional rolling, and motile microcilia widely existed in mammals' body for active matter transportation through in situ oscillation. Till now, bionic studies have been extensively performed by imitating a single specific biologic functional system. However, bionic fabrication of devices integrating multispecies architectures is rarely reported, which may sparkle more fascinating functionalities beyond natural findings. Here, a cross-species design strategy is adopted by combining the anisotropic wettability of the rice leaf surface and the directional transportation characteristics of motile cilia. High-aspect-ratio magnetically responsive microcolumn array (HAR-MRMA) is prepared for active droplet transportation. It is found that just like the motile microcilia, the unidirectional waves are formed by the real-time reconstruction of the microcolumn array under the moving magnetic field, enabling droplet (1-6 µL) to transport along the predetermined anisotropic orbit. Meanwhile, on-demand droplet horizontal transportation on the inclined plane can be realized by the rice leaf-like anisotropic surface, showcasing active nongravity-driven droplet transportation capability of the HAR-MRMA. The directional lossless transportation of droplet holds great potential in the fields of microfluidics, chemical microreaction, and intelligent droplet control system.