Multifunctional polyimide-based femtosecond laser micro/nanostructured films with triple Janus properties

Chemical magnetism - surface force to move motors

If redox reactions occur on the surface of a motor and a current loop arises, then in a non-uniform magnetic field, in addition to the usual magnetic force, such a motor will also be affected by a chemical magnetic force. The chemical magnetic force belongs to the class of surface forces. Here we analyze for the first time the properties of chemical magnets, which consist of three dissimilar metals, as well as the magnetic field generated by a chemical magnet using paramagnetic nanoparticles. The results of the study show that the chemical magnetic force depends on the concentration and type of electrolyte, the pH of the solution, the temperature, and the structure of the chemical magnet. The results obtained can contribute to the creation of devices where chemical energy is directly converted into kinetic energy of motion.

Alcohol-gating femtosecond laser-induced micro/nano-structured membranes with reversible switching wettability and breathability

A reversible liquid gating membrane with the ability to regulate gas/liquid transport is critical for many fields, such as biological applications, multiphase separation, and sewerage treatment. Numerous membranes can respond to external stimuli and dynamically control gas/liquid fluid transport; however, simultaneously achieving regulated gas/liquid transport membranes through simple manufacturing remains a challenge. In this work, we investigated an alcohol-regulation gating membrane via femtosecond laser one-step processing, allowing in situ dynamically controllable gas/liquid transfer. More specifically, the porous membrane, processed by laser, exhibits excellent superhydrophobicity (WCA ∼ 153.4°) and breathability (water-vapor evaporation rates ∼118.3 mg (cm2 h)-1), enabling gas to penetrate but not water. In contrast, it allows the passage of water while preventing the permeation of gas subsequent to the introduction of alcohol. Furthermore, the porous membrane still possesses superbly consistent performance after being placed in air for 90 days or over 100 dropping-drying ethanol cycles test, indicating outstanding durability and reversibility. Significantly, the porous membrane has broad potential applications in medical dressings, providing a new strategy to fabricate next-generation bandages.

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.

Anti-icing performance of hydrophobic coatings on stainless steel surfaces

This study aims to prevent ice accumulation on the surface of drilling tools by investigating the effectiveness of hydrophobic coatings, which is one of the most promising methods to solve drilling difficulties in warm ice. Herein, four types of hydrophobic organic coatings that can be used on metal surfaces were tested to evaluate their anti-icing performance, service durability, and friction properties. All of them possess rough surfaces with microstructure characteristics such as pores, stripes, or micropapillae. They also exhibit hydrophobicity, with water contact angles of 101.6°, 100.0°, 103.1°, and 108.5°. They can significantly prolong the required freezing time of water droplets on their surfaces, effectively reduce ice adhesion, and decrease the friction between ice and their surface. The ice adhesion in the axial, tensile, and tangential directions can be reduced by 65.64 %, 56.31 %, and 72.11 %, respectively, for the coating with silicon (Si)-based and fluorine (F)-containin compounds (coating-C) at -30 °C; while it can be reduced by 85.05 %, 73.9 %, and 94.2 %, respectively, for the coatings with Si-based and polytetrafluoroethylene (PTFE) compounds (coating-D). The two coatings mentioned above lose their anti-icing performance after 20 icing and de-icing cycles, and their hydrophobicity after 120 abrasion cycles under a load of 6 N.

Photothermal Conversion of the Oleophilic PVDF/Ti3C2Tx Porous Foam Enables Non-Aqueous Liquid System Applicable Actuator

Various physical and chemical reaction processes occur in non-aqueous liquid systems, particularly in oil phase systems. Therefore, achieving efficient, accurate, controllable, and cost-effective movement and transfer of substances in the oil phase is crucial. Liquid-phase photothermal actuators (LPAs) are commonly used for material transport in liquid-phase systems due to their remote operability and precise control. However, existing LPAs typically rely on materials like hydrogels and flexible polymers, commonly unsuitable for non-aqueous liquids. Herein, a 3D porous poly(vinylidene fluoride) (PVDF)/Ti3C2Tx actuator is developed using a solvent displacement method. It demonstrates directional movement and controlled material transport in non-aqueous liquid systems. When subject to infrared light irradiation (2.0 W cm-2), the actuator achieves motion velocities of 7.3 and 6 mm s-1 vertically and horizontally, respectively. The actuator's controllable motion capability is primarily attributed to the foam's oil-wettable properties, 3D porous oil transport network, and the excellent photothermal conversion performance of Ti3C2Tx, facilitating thermal diffusion and the Marangoni effect. Apart from multidimensional directions, the actuator enables material delivery and obstacle avoidance by transporting and releasing target objects to a predetermined position. Hence, the developed controllable actuator offers a viable solution for effective motion control and material handling in non-aqueous liquid environments.

Recent advances in functional micro/nanomaterials for removal of crude oil via thermal effects

Crude oil is one of the most widely used energy and industrial raw materials that is crucial to the world economy, and is used to produce various petroleum products. However, crude oil often spills during extraction, transportation and use, causing negative impacts on the environment. Thus, there is a high demand for products to remediate leaked crude oil. Among them, oleophilic and hydrophobic adsorbents can absorb crude oil through thermal effects and are research hotspots. In this review, we first present an overview of wettability theory, the heating principles of various thermal effects, and the theory of reducing crude oil viscosity by heating. Then we discuss adsorbents based on different heating methods including the photothermal effect, Joule heating effect, alternating magnetic field heating effect, and composite heating effect. Preparation methods and oil adsorption performance of adsorbents are summarized. Finally, the advantages and disadvantages of various heating methods are briefly summarized, as well as the prospects for future research.

Airflow Triggered Water Film Self-Sculpturing on Femtosecond Laser-Induced Heterogeneously Wetted Micro/Nanostructured Surfaces

Liquid manipulation is essential for daily life and modern industry, and it is widely used in various fields, including seawater desalination, microfluidic robots, and biomedical engineering. Nevertheless, the current research focuses on the manipulation of individual droplets. There are a few projects for water film management. Here, we proposed a facile method of wind-triggered water film self-sculpturing based on a heterogeneous wettability surface, which is achieved by the femtosecond laser direct writing technology and femtosecond laser deposition. Under the conditions of various airflow velocities and water film thicknesses, three distinct behaviors of the water film were analyzed. As a result, when the water film thickness is lower than 4.9 mm, the self-sculpture process will occur until the whole superhydrophobic surface dewetting. Four potential applications are demonstrated, including encryption, oil containers, reconfigurable patterning, and self-splitting devices. This work provides a new approach for manipulating a water film of fluid control engineering.

Advanced Fog Harvesting Method by Coupling Plasma and Micro/Nano Materials

Harvesting fog is a potential and effective way to alleviate the crisis of water resource shortage. A highly efficient and economical fog harvesting method has always been a global and common goal. Here, a promising fog harvesting method by coupling plasma and micro/nano materials is proposed, which can achieve 93% fog collection efficiency with consuming power of only 0.76 W/0.04 m2. The basic method is to utilize nanoparticles to decorate both the discharge electrode and the collecting electrode of the micro/nano electrostatic fog collector. For the discharge electrode, the nanoparticles can achieve an order of magnitude higher electric field strength and a 28.6% decrease in the operating voltage (14 kV decreases to 10 kV). For the collecting electrode, a novel composite structure of hydrophobic/hydrophilic (HB/HL) is proposed. The core advantage is the directional droplet transport at the junction of HB and HL caused by surface tension can adjust the accumulated droplets on the two sides, which avoids the droplet residue and mesh blockage in the general structure. This technology provides an innovative approach for the collection of microdroplets and a new design idea for the fog collector to deal with the water crisis.

Armored Superhydrophobic Surfaces with Excellent Drag Reduction in Complex Environmental Conditions

Superhydrophobic surfaces (SHSs) have possibilities for achieving significantly reduced solid-liquid frictional drag in the marine sector due to their excellent water-repelling properties. Although the stability of SHSs plays a key role in drag reduction, little consideration was given to the effect of extreme environments on the ability of SHSs to achieve drag reduction underwater, particularly when subjected to acidic conditions. Here, we propose interconnected microstructures to protect superhydrophobic coatings with the aim of enhancing the stability of SHSs in extreme environments. The stability of armored SHSs (ASHSs) was demonstrated by the contact angle and bounce time of droplets on superhydrophobic surfaces treated by various methods, resulting in an ASHS surface with excellent stability under extreme environmental conditions. Additionally, inspired by microstructures protecting superhydrophobic nanomaterials from frictional wear, the armored superhydrophobic spheres (ASSPs) were designed to explain from theoretical and experimental perspectives why ASSPs can achieve sustainable drag reduction and demonstrate that the ASSPs can achieve drag reduction of over 90.4% at a Reynolds number of 6.25 × 104 by conducting water entry experiments on spheres treated in various solutions. These studies promote a fundamental understanding of what drives the application of SHSs under extreme environmental conditions and provide practical strategies to maximize frictional drag reduction.