Micro-nano Composite Structures Research Articles

A comparative study of flow boiling performance in smooth and multi-stage enhanced open microchannels

Flow boiling in open microchannels is currently one of the research focuses in the field of phase-change heat transfer. The present paper described a comparative and experimental research on flow boiling heat transfer of SF-33, an environmentally friendly working fluid, in smooth surfaces open microchannels (SOM) and multi-stage enhanced open microchannels (MSEOM). The study investigated the flow boiling performance of SF-33 in two open microchannels with different mass fluxes, heat fluxes and inlet subcooling. The different boiling flow patterns in two open microchannels were analyzed with high-speed visualization. The results indicated that under different inlet cooling conditions, the MSEOM improved the flow boiling heat transfer performance significantly and improved the wall temperature uniformity. The visualization images indicated that the flow pattern transition was different due to the different surface structures of two open microchannels. The SOM experienced plug-stratified flow at high heat flux, while MSEOM transformed into churn flow due to its sintered copper powder and wire mesh micro-nanocomposite structures. The multi-stage enhanced structures exhibited excellent hydrophilicity and wicking capability, leading to a less pressure drop in the MSEOM compared with that in SOM. The pressure drops for both open microchannels decreased as inlet subcooling increased.

Enhancing durability of superhydrophobic surfaces via nanoparticle-induced bipolar interface effects and micro-nano composite structures: A femtosecond laser and chemical modification approach

Superhydrophobic coatings are vital in energy, aerospace, and chemical engineering, while their complex preparation and limited durability hinder widespread application. Therefore, inspired by the unique structures of hydrophobic cotton surfaces and mosquito eyes in nature, a durable aluminum alloy superhydrophobic surface is developed using a combination of femtosecond laser and chemical modification methods. Initially, porous microneedle micro-nanostructures are ablated on the surface of the aluminum alloy via femtosecond laser technology. Then, epoxy resin modified with γ-aminopropyl triethoxysilane (KH550) forms a covalently bonded intermediate layer. Finally, biphasic silicon dioxide (BP-SiO2) nanoparticles modified by hexadecyltrimethoxysilane (HDTMS) are used to construct the top hydrophobic layer. The covalent interface interactions between the aluminum alloy substrate and the intermediate layer, as well as between the intermediate layer and the top layer, significantly enhance the durability of the superhydrophobic surface. The prepared F-M@KH-EP/BP-SiO2 coating exhibits outstanding superhydrophobic properties, with a water contact angle (CA) as high as 168.56° and a sliding angle (SA) as low as 1.52° More encouragingly, the composite coating maintains its excellent water resistance even when subjected to harsh mechanical durability damage, including sandpaper wear, tape stripping tests, water drop and sand impact tests. Moreover, the prepared coatings maintain distinguished non-wettability in harsh operating conditions such as corrosive liquid environments, ultraviolet radiation, ultrasonic vibration, etc. Additionally, the coating demonstrates remarkable self-cleaning properties. Superhydrophobic surface durability is significantly enhanced by combining nanoparticle-induced bipolar interface effect and micro-nano structures. These findings provide theoretical reference for the design and application of durable superhydrophobic coatings.

Acid wet blasting method for fabricating superhydrophobic aluminum surface with micro-nano composite structures

Acid wet blasting method for fabricating superhydrophobic aluminum surface with micro-nano composite structures

Mechanisms of metal wettability transition and fabrication of durable superwetting/superhydrophilic metal surfaces

Maintaining superhydrophilicity on metal surfaces is challenging due to the inevitable surface adsorption of airborne organics after exposure to ambient air. In this study, we aim to elucidate the mechanisms underlying the persistence of surface superhydrophilicity and propose a technique for the preparation of durable superwetting/superhydrophilic metal surfaces. The effects of atmospheric organic properties, including the type of functional groups and the length of the carbon chain, on the rate of wettability transition and the final surface wettability after the surface adsorption are first investigated. Molecular dynamics simulation is used to explain why long-chain organics can lead to more marked wettability transitions. The liquid wetting and organic diffusion on textured surfaces are then analyzed, which proves that conventional surface structures with only single-scale structural features are challenging to achieve long-lasting superhydrophilicity. Finally, an in-situ laser deposition technique is proposed to fabricate micro-nano composite porous structures, in which the microstructures promote liquid wetting and the nanostructures inhibit organic diffusion. The prepared surfaces exhibited a 54-fold enhancement in the duration of surface superhydrophilicity compared to conventional nanostructures. Our results help to understand the mechanisms of durable superhydrophilicity, which are beneficial for the practical applications of superwetting/superhydrophilic surfaces.

Exploring the potential of micro-nano composite structures for COVID-19 vaccines and beyond.

Exploring the potential of micro-nano composite structures for COVID-19 vaccines and beyond.

Long-Range Uniform SiCxOy Beaded Carbon Fibers for Efficient Microwave Absorption.

SiCxOy beaded carbon fibers were successfully fabricated for the first time using a facile and stable electrospinning and temperature process. The resulting fibers showcase a unique micro-nanocomposite structure, in which β-SiC beads with a silica-enriched surface are strung together with defect carbon fibers, as confirmed by XRD, XPS, and HRTEM investigation. The SiCxOy beaded carbon fibers display efficient microwave absorption performance, with a minimum reflection loss of -58.53 dB and an effective absorption bandwidth of 5.92 GHz. A modified Drude-Lorentz model was developed for SiCxOy beaded carbon fibers to reveal the double-peaked feature of the permittivity of these fibers, which is in good agreement with experimental measurements. Moreover, simulations were performed to extract polarized electric fields and microwave energy volume losses within a typical distribution of SiCxOy beaded carbon fibers. It is concluded that the dipole relaxation and hopping migration of localized electrons give a superior contribution to the overall decay of the microwave energy. This study indicates that SiCxOy beaded carbon fibers with a unique micro-nanocomposite structure hold great promise for microwave absorption applications. Additionally, this fabrication strategy offers a unique approach to producing micro-nanocomposite structures and highlights their potential applications.

An investigation on the adhesion of dual-scale micro-nano composite structure on the surface of aluminum

Adhesion is a crucial characteristic of hydrophobic surfaces that significantly impacts their practical applications. This paper proposes an innovative method for preparing a dual-scale micro-nano composite structure surface by combining mechanical ruling and anodic oxidation, which demonstrates great potential in enhancing hydrophobic surface properties. Through the analysis of the influence of micro-groove depth on the adhesion of hydrophobic surfaces, it has been discovered that micro-groove dimensions can be used to control surface adhesion while maintaining hydrophobicity, without complex chemical modifications. These findings present a promising approach for tailoring the properties of hydrophobic surfaces to suit specific applications. Compared with the single-scale micro-groove array structures, the surface roughness of the dual-scale micro-nano composite structures is significantly increased, and the contact angle of the water droplet is significantly increased. At the same time, the hydrophobicity and adhesion of the surface of the dual-scale micro-nano composite structures were analyzed. The results show that after anodizing, the contact angle of the dual-scale micro-nano composite structure surface increases, and the surface adhesion can be controlled by adjusting the structural parameters of the micro-groove and the anodizing process parameters, to ensure that the surface presents hydrophobic property while realizing the controllable adhesion of the hydrophobic surface. In this paper, dual-scale micro-nano composite structures fabricated by the composite method have achieved hydrophobic properties, and the surface adhesion can be effectively controlled by adjusting the processing parameters. This method has certain reference significance for the preparation of the controllable adhesive hydrophobic surface and lays a foundation for the further study of the controllable adhesive hydrophobic surface.

Mesoscale Simulations on the Ultrahigh Heat Flux Evaporation of R143a within Ultrathin Nanoporous Membrane Using a Modified Dimensionless Lattice Boltzmann Method

A modified dimensionless pseudo-potential lattice Boltzmann method capable of restoring all related thermophysical properties of any working fluid and spatial/temporal scales of the computational domain is developed in this work. Direct numerical investigations of ultrathin liquid film evaporation of R143a within nanoporous membranes to its ambient pure vapor are carried out. The characteristics of evaporation-driven replenishing flow and the self-regulation of liquid-vapor interface profile under different heat fluxes are captured. In the case of intensive ultrathin liquid film evaporation within nanopore, the apparent contact angle could not reach as small as Young's contact angle θ0 for isothermal conditions due to the self-regulation of liquid-vapor interface. As a result, the maximum capability of nanoporous membranes to replenish the liquid is limited. Under the ambient temperature T0 = 318.19 K, before the three-phase contact line (TCL) recedes into the nanoporous membrane, a heat flux as high as qin,max = 1.52 kW/cm2 can be sustained with a superheat about Ts = 7.79 K for a membrane with pore radius rp = 38.71 nm, pore depth Lp = 294.96 nm, Young's contact angle θ0 = 23° and porosity η = 0.66. The maximum heat flux qin,max increases with the increase of rp and the decrease of Lp and θ0. The present work presents a promising numerical method to optimize thermal management devices using complex micro-nano composite structures.

Hydrophobic and corrosion resistance properties of the electrochemically etched Zr-based bulk metallic glasses after annealing and cryogenic thermal cycling treatment

The effects of annealing and cryogenic thermal cycling treated on hydrophobic properties of Zr-based bulk metallic glasses surfaces fabricated by electrochemical etching were studied. The cryogenic thermal cycling on leads to poor corrosion performance for heat-treated metallic samples, while the annealing treatment induces the improved corrosion performance. Under the same electrochemical etching process, the etched sample surface is covered by dense coral-like micro-nano composite structures after cryogenic thermal cycling treatment for 30 cycles, and achieves superhydrophobic. However, there almost no nanoscale structures appear on the sample surface heat-treated at 702 K which results in the poor hydrophobic properties. Superhydrophobic film can generate a corrosion protection due to the existence of micro-nano composite structures in the samples.

Gentle fabrication of colorful superhydrophobic bamboo based on metal-organic framework

The efficient use of abundant renewable bamboo as high value-added decoration and building materials is of great significance for mitigating carbon dioxide emissions and maintaining sustainable development. The key challenge is to explore efficient and gentle methods to improve the undesirable surface properties of bamboo. Herein, a colorful and superhydrophobic bamboo is gently fabricated by a facile in-situ growth and conversion method based on metal-organic framework (for constructing micro-nano composite structures) and subsequent coating of sodium laurate (for reducing surface energy) at room temperature. The resulting sodium laurate-coated cobalt-nickel double hydroxide layer (CoNi-DH-La) is demonstrated as an efficient superhydrophobic layer to exhibit excellent chemical and mechanical stability. Impressively, the as-obtained CoNi-DH-La-coated bamboo sheet (BS-CoNi-DH-La) shows positive performances in terms of mildew resistance, flame retardancy, and self-cleaning. More importantly, this gentle method can endow bamboo with multiple unfading colors by changing the type of inorganic salts during the preparation process and display good potential for large-scale production.

In situ formation of tetraphenylethylene nano-structures on microgels inside living cells via reduction-responsive self-assembly.

Controlling the assembly of synthetic molecules in living systems is of significance for their adaptive applications. However, it is difficult to achieve, especially for composite self-assemblies, due to the complexity and dynamic change of the intracellular environment, and there exist technical difficulties for the direct visualization of organic and polymer self-assemblies. Herein, we demonstrate a novel strategy for the in situ formation of self-assembled micro-nano composite structures in a cell milieu using reduction-responsive microgels (MGs) as a platform. The MGs were prepared by a templating and crosslinking method using a synthetic amphiphlic polymer as the basic material and porous CaCO3 microparticles as the template. The aggregation-induced emission (AIE) tetraphenylethylene moieties and reduction-labile disulfide bonds in the MGs were employed as the self-assembly building blocks and triggering sites for the intracellular self-assembly, respectively. In the presence of reductive agents such as glutathione, nano-spikes were gradually formed on the MGs. After the MGs were internalized by cells, the in situ formation of microgel/nano-spike composite structures was evidenced by the enhanced fluorescence intensity and was further confirmed by direct transmission electron microscopy observation. This work provides an effective strategy to cope with the challenging task of achieving and probing controlled self-assembly in a cell milieu, leading to new insights into investigating biological self-assembly and promoting the development of micro-/nanomaterials by learning from nature.

Regulation of hydrophobicity on yttria stabilized zirconia surface by femtosecond laser

Superhydrophobic surfaces have received extensive attention owing to their excellent properties. In this study, yttria stabilized zirconia (YSZ) surfaces with micro-nano composite structures were prepared by one-step laser texturing. Laser texturing greatly improved the hydrophobicity of YSZ surface. Contact angle of the surface increased from 86.7° to 151.8°, indicating the transition from hydrophilic to superhydrophobic surface. Surface chemical analysis indicated that the enhancement of surface hydrophobicity can be attributed to the decrease in surface polarity, caused by changes in the ratio of chemical components adsorbed from the air and the formation of micro-nano composite structures. Laser texturing effectively regulated the hydrophobicity of YSZ surface, thereby providing promising strategy for corrosion resistance research of thermal barrier coatings.

The effect of SiO2 particles on electrical properties of superhydrophobic antiflash coatings

In this paper, the effect of SiO2 particles on electrical properties of superhydrophobic antiflash coatings was studied, which electrical properties include, the volume resistivity (ρ v), the electrical strength (U B), relative permittivity (ε r), and the dielectric dissipation factor (tanδ). This kind of superhydrophobic coating uses modified SiO2 and TiO2 particles to construct micro-nano composite structures on the surface of FEVE fluorocarbon resin, and its surface has superhydrophobic characteristics. The results show that, with the addition of 5um SiO2 content, ρ v of the coating showed a trend of first increasing and then decreasing. The amount of 20 nm SiO2 particles added has little effect on ρ v. The content of 5um and 20 nm SiO2 has little influence on the U B of the coating. With the increase of 5um and 20 nm SiO2, ε r and the tangent of tanδ show an increasing trend. Compared with 5um SiO2, 20nm SiO2 has less influence on tanδ. The addition of 80nm SiO2 has obvious significantly adverse effects on the four electrical properties of the coating.

Study on the Creation of Fine Periodic Structure on V-Shaped Groove with Short-Pulsed Laser

Functional surface creation technologies have garnered increasing attention over the years. These technologies can provide various functions to a material by establishing a fine structure on the material surface and responding to the needs of industrial products with distinguished functions or high values. In addition, by creating a “composite fine structure,” which is composed of two kinds of structures with different scales, the enhancement of functions and emergence of new functionalities can be expected. Hence, our study combined a micrometer-scale V-shaped groove structure using an ultra-precision cutting and nanometer-scale ultra-fine periodic structure (LIPSS) using a short-pulsed laser. Then, we clarified the creation principle and studied the functionality of the structure, specifically, its wettability. As a result, it was found that optical behavior inside the V-shaped groove changed; therefore, the composite structure changed depending on the groove angle, laser polarization direction, and number of times of irradiation. In addition, it was found that the water wettability changed depending on the type of formed micro-nano composite structures. Moreover, the wettability could be controlled by depending on how the structure is used.

One-pot mussel-inspiration and silication: A platform for constructing oil-repellent surfaces toward crude oil/water separation

Superhydrophilic filters with excellent subaqueous oil-repellent surfaces are of great significance in the field of crude oil/water separation. Their pore size should be matched with the separation target (smaller than the oil droplets) based on the “size sieving” principle. However, it is a tricky task to facilely and flexibly tune the pore size of filters to effectively separate oily wastewater containing crude oil droplets with different sizes in practice. Herein, a universal platform based on the one-pot mussel-inspiration and silication has been verified to prepare free-standing nanofilms at the air/water interface and deposited coatings on the polypropylene microfiltration membrane or the copper mesh simultaneously. The evolution of chemistries and morphologies of the free-standing films and the deposited coatings is in real-time monitored to deeply understand the formation of the surfaces. We suggest the mussel-inspiration and the silication is asynchronous, being responsible for the formation of the nanofilm and coating surfaces with tunable hydrophilic moieties and micro-nano composite structures. These structure characteristics endow the surfaces with a superhydrophilicity/superoleophobicity underwater and with a low crude oil adhesion especially in basic aqueous environment or salty water regardless of the salt type. The free-standing nanofilms with nano-sized intervals are able to reject nano-droplets from the crude oil-in-water nanoemulsions. The coated polypropylene microfiltration membrane and copper mesh can be applied in oil-in-water microemulsions and oil/water mixtures separation, respectively. All filters show a highly efficient oil repellence of crude oil (>99%) during the separation. This work contributes a promising concept of a one-pot fabrication methodology for fulfilling task-specific requirements of crude oil/water separation.

Multi-scale micro-nano structures prepared by laser cleaning assisted laser ablation for broadband ultralow reflectivity silicon surfaces in ambient air

To meet the ultra-broadband perfect absorption of visible-infrared light on silicon surfaces, a green, efficient and economical method for fabricating multi-scale micro-nano composite structures in ambient air is proposed. We experimentally demonstrate laser cleaning assisted femtosecond laser ablation for fabricating anti-reflection structures. Laser cleaning technology not only effectively eliminates oxide deposition on the laser textured surfaces, but also manufactures the small scale fine-microstructures and nanostructures. A focused ellipse laser spot is innovatively applied to realize large area and energy decays continuously multiple laser cleaning of laser-treated surfaces, and solve the problem that new oxide deposition is generated in the cleaning process. The processing efficiency is also increased by 4.8 times. The average reflectance of 2.06% is reached from 300 to 2500 nm. Great enhancement of infrared light absorption of silicon from 2.5 to 16 μm is realized experimentally. The average reflectance is reduced to 4.98% with a broadband reflectance below 6.6%. Especially, a reflectance below 5.0% from 2.5 to 10 μm and an average reflectance of 4.3% is achieved, which is the least reported to date by laser processing techniques as far as we know. This strategy for anti-reflection structures is excellent candidate for future optoelectronic devices.

Fabrication of diamond ultra-fine structures by femtosecond laser

A 400 nm femtosecond laser was used to ablate the surface of a high-pressure and high-temperature diamond, and subwavelength surface micro structures with a period of 100 nm were achieved. A variety of micro-nano composite surface structures were prepared by changing the polarization direction and laser scanning direction. By dynamically adjusting the laser polarization and the laser scanning tracks, a maskless direct writing fabrication of micro-nano complex structures was realized. The micro-nano patterning on an ultra-hard and super-stabile diamond provides a new idea for the preparation of friction reducing surfaces, nano imprint transfer templates, surface enhanced Raman scattering test substrates, and micro-nano optical structures.

Preparation of Superhydrophobic Multiscale Films for Oil-Water Separation in a Harsh Environment

The problem of oil-water separation regarding oil-containing brine has been of much concern when using the oil pad water dissolution method to construct salt cavern reservoirs. In this paper, oil-water separation materials with micro-nano hierarchical structure were prepared on different metal substrates using chemical etching and electrophoretic deposition. And hydrophobic materials with a single micro/nano structure were also prepared; then, the surfaces were hydrophobized by various low surface energy modifiers. Thereafter, we analyzed and compared the surface morphology, chemical composition, and wettability of all the materials and found that brine contact angles on hierarchical structure surfaces were above 160° while the diesel was completely diffused. Furthermore, preparation parameters affecting the surface morphology and wettability of micro-nano composite structures were explored. Meanwhile, it was found that the surface of prepared composite structure could still maintain super-hydrophobic/lipophilic properties after exposure in air for 6 months, sliding 60 cm on sandpaper, or immersion in diesel/brine for 48 h. Moreover, the composite structure surface displayed improved corrosion resistance with corrected self-corrosion potential and lower corrosion current density. It was equally observed that the studied materials could be better adapted to the actual context of salt cavern reservoir construction and thus have great application prospects.

Efficient water scavenging by cooling superhydrophobic surfaces to obtain jumping water droplets from air

Dew collection is significant in harvesting water and relieving water shortages in arid regions. However, current methods for collecting dew or steam are mainly focusing on the millimeter-sized droplets condensed on the superhydrophobic surfaces. Here, we present a concept for harvesting micro droplets that can spontaneously bounce on the cooling superhydrophobic aluminum surface with randomly micro-nano composite structures, which were fabricated by using a two-step surface structural process. Moreover, an integrated device has been developed, which consists of a triboelectric nanogenerator and the superhydrophobic aluminum sheet. We experimentally explained that the triboelectric nanogenerator, which provides an external electric field by converting wind energy to electric energy with DC voltage pulse peaks of about 60 V, can be utilized to enhance the collection capacity of the jumping water droplets.

多形貌多周期微纳米复合结构的制备及表征

多形貌多周期微纳米复合结构的制备及表征