Dual-scale Structure Research Articles

High-Temperature-Resistant Dual-Scale Ceramic Nanofiber Films toward Improved Air Filtration.

Currently, air pollution primarily arises from industrial emissions, coal combustion, and automobile exhaust, posing significant challenges for mitigation. This highlights the urgent need for advanced and efficient filtration materials with low pressure drop and high-temperature resistance. Traditionally, improving filtration property has involved increasing the thickness of the filtration materials, which consequently leads to higher costs. Here, dual-scale mullite nanofiber (MNF) films containing interwoven thick nanofibers (606 nm) and thin nanofibers (186 nm) are prepared using solution blow spinning. The dual-scale structure design enables the films to maintain a low pressure drop while achieving high filtration efficiency. At an airflow velocity of 5.3 cm s-1, the films with an areal density of 3.8 mg cm-2, achieve a filtration efficiency of 98.23% and a pressure drop of 141 Pa for PM0.3. In addition, the MNF films exhibit excellent flexibility and high-temperature resistance, making them have great potential for use in high-temperature flue gas filtration.

Fabrication of TiN-doped Ti nanocomposites with high strength and ductility by plasma-assisted ball milling and laser powder bed fusion

An efficient method to fabricate titanium nitride (TiN)-doped titanium (Ti) nanocomposites through a combination of plasma milling, plasma spheroidization, and laser powder bed fusion (LPBF) was developed to obtain Ti-based materials with high strength and ductility from commercially pure titanium (CP-Ti). Nitrogen plasma milling and plasma spheroidization were used to fabricate Ti-TiN nanocomposites, which were mixed with CP-Ti powder at a 1:9 ratio and printed by LPBF forming. The resulting materials possessed a dual-scale morphology with both coarse lath-like and fine acicular-like grains. The Ti-TiN nanocomposites possessed higher hardness and tensile strength and lower ductility than those of the control sample without TiN. The mechanical properties of the LPBF-printed Ti-TiN nanocomposites were improved compared with those of LPBF-printed CP-Ti because of the TiN particles and resulting dual-scale structure. Nitrogen plasma milling provides a simple route to fabricate TiN nanophase-reinforced Ti-based nanocomposites suitable for LPBF printing.Graphical

Superhydrophobicity induced antibacterial adhesion and durability of laser bidirectionally-textured zirconia surfaces with different inclination angles

Femtosecond laser bidirectional texturing with different laser energy densities and inclination angles was performed on zirconia (ZrO2) surfaces. The laser bidirectional texturing models under different inclination angles were constructed to predict the water contact angles (WCAs), and the superhydrophobicity induced antibacterial adhesion mechanism was analyzed. The results revealed that under the combined effect of the optimal laser energy density (7.0 J/cm2) and inclination angle (90°), the laser-textured ZrO2 surface could obtain a micro-nano dual-scale structure composed of periodic regular micro-cones and nanoparticles. This structure not only promoted the adsorption of carbon-containing hydrophobic groups from the stearic acid and the air to form a superhydrophobic surface with excellent chemical/mechanical durability and anti-fouling/self-cleaning abilities, but also minimized the contact area with the bacterial suspension (solid/liquid contact area ratio of 6 %) to enhance antibacterial ability. The optimal stearic acid-modified laser-textured ZrO2 surface exhibited an extremely low adhesive force (Fadhesive=6.69 μN) to the bacterial suspension, and thus achieved the highest antibacterial ratio of 85.3 %. This study is expected to enrich the application of ZrO2 ceramics in the medical field.

Excellent thermal, moisture-permeable weft-knitted fabric with core-sheath yarn structure for foot protection in cold environments

In extremely cold environments, maintaining body temperature and reducing heat dissipation is essential for maintaining human health and life safety, but the field of thermal insulation shoe upper fabric has not been deeply studied. In this paper, based on the dual-scale structure of the yarn and shoe upper fabric, a composite yarn with a core-sheath structure is designed, and a using plating stitch pattern weft-knitted whole garment thermal insulation shoe upper fabric with double-layer structure is proposed. By testing the mechanical properties and thermal and moisture performance of the shoe upper fabric and the thermal insulation performance of the whole shoe, the thermal insulation mechanism of the weft-knitted whole garment shoe upper fabric with a double-layer structure and dual-scale structure design was systematically studied. The results show that the shoes made of polyimide/hollow polyester composite yarn with core-sheath structure yarn have good thermal insulation performance. The use of core-sheath yarns can improve the thermal insulation performance of the shoe, and, with the increase of the ratio of core-sheath yarn, the thermal insulation performance of the shoe is better. Starting from the dual-scale shoe fabric structure, this article proposes a novel method for the industrial production of thermal insulation shoe upper fabrics, which is expected to provide guidance for the further development of thermal insulation shoe upper fabric in the future.

The Preparation and Properties of a Ni-SiO2 Superamphiphobic Coating Obtained by Electrodeposition

Superamphiphobic coatings have shown great potential in many fields such as with their anti-corrosion, high-temperature resistance, self-cleaning, and drag reduction properties. However, due to the poor stability of their coatings, it is difficult to apply them on a large scale. In this paper, two kinds of SiO2 particles and nickel were co-deposited on the surface of steel to construct a micro/nano dual-scale structure by composite electrodeposition. The surface of the coating was then fluorinated with the low-surface-energy material 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (AC-FAS) to prepare a Ni-SiO2 superamphiphobic coating. The coating has a water contact angle of 159° and an oil contact angle of 151°. The effect of nanoparticle concentration on the wettability and surface morphology of the coating was systematically studied. Comparative experiments revealed that the optimal micro/nanoparticle concentrations were 8 g/L of 20 nm SiO2 and 2 g/L of 1 μm SiO2. This preparation method greatly improves the corrosion resistance, wear resistance, chemical stability, and high-temperature resistance of the coating.

Regulation mechanism of droplets wetting on banana leaf surface and its dynamic contact angle wetting model

The effective wetting and deposition of pesticide droplets on the leaf surface significantly affect the control of pests and diseases, and its mainly affected by the leaf surface properties and pesticide formulation properties. This article aims to investigate the wettability regulation mechanism and dynamic wetting properties of banana leaves, in order to intelligently design appropriate pesticide formulations. The micro-morphology of the banana leaves exhibits a micro-nano dual-scale structure with different microstructures and roughness on the adaxial side and abaxial side. Correspondingly, the wettability on the adaxial side of the banana leaf with higher roughness (Rq = 71.1 nm) is always better than that on the abaxial side (Rq = 42.5 nm). The droplet contact performance of droplets exhibits a strong concentration dependence of surfactants, which regulate the inter-species differences in the wettability of different pesticide formulations on both sides. Besides, the dynamic wetting process of pesticide droplets exhibits strong time dependence, by using a time series method to establish an AR(2) model, precise simulation and prediction of the contact angle changes on the adaxial side (R2 = 0.9560) and abaxial side (R2 = 0.8903) during the dynamic wetting process were achieved. The dynamic wetting model provides new insights into the spreading and deposition processes of droplets on leaves. This work provides a favorable reference for the study of the dynamic balance between wetting and adhesion properties of pesticide spray on leaf surfaces.

Fabrication and Temporal Dependency Osteogenic Regulation of Dual-Scale Hierarchical Microstructures on Medical Metal Surface.

The structural characteristics at the interface of bone implants can guide biological regulation. In this study, a dual-scale hierarchical microstructure is proposed and customized using hybrid machining to achieve temporal dependency osteogenic regulation. It is observed that osteoblasts induced by dual-scale hierarchical structure exhibit adequate protrusion development and rapid cell attachment through the modulation of mechanical forces in the cell growth environment, and further promot the upregulation of the cell membrane receptor PDGFR-α, which is related to cell proliferation. Afterward, transcriptomic analysis reveals that during the differentiation stage, the DSH structure regulates cellular signaling cascades primarily through integrin adhesion mechanisms and then accelerates osteogenic differentiation by activating the TGF-β pathway and cAMP signaling pathway. Furthermore, the calcium nodules are preferentially deposited within the lower honeycomb-like channels, thereby endowing the proposed dual-scale hierarchical structure with the potential to induce oriented deposition and improve the long-term stability of the implant.

Smart wetting based on thermal-induced dual-scale surfaces

Surfaces wettability influences drag reduction in engineering applications, and surface structure largely determines the wetting properties. This study proposes a novel thermal shape memory polymer (TSMP) with dual-scale structure surface capable of reversible transformation via working temperature. A preparation method for TSMP with micro-nano dual-scale structure is also proposed to enhance hydrophobicity comparing with microstructure. Experimental results indicate TSMP micro-nanostructure surfaces achieve reversible conversion between hydrophilicity and hydrophobicity, TSMPs with micro-nano structure also exhibit good recovery. Simulation was established to understand tunable wettability and fluid flow mechanisms of TSMP reversible two-phase microstructures aiding design of TSMP microstructures with adjustable wettability.

Video anomaly detection guided by clustering learning

With the fuzzy boundary between normal and abnormal video data, which cannot be well distinguished by most methods, anomaly detection in video requires better characterization of the data. First we give a convolution-enhanced self-attentive video auto-encoder based on the U-Net architecture, which can extract richer image features. Secondly we design a dual-scale feature clustering structure for this encoder, which simultaneously compresses the channel and spatial structure features of the image to represent the features to obtain good coding characteristics and expand the boundary between normal and abnormal data. We also verify that our approach is equivalent to a class of auto-encoders for memory-guided learning. Finally, in the reconstruction task, since video auto-encoders are capable of triggering temporal time leakage phenomena that can lead to network performance degradation, we propose an anomaly score computation paradigm for video auto-encoders that utilizes the average frame anomaly score of a video clip to compute the first frame anomaly score in that video clip.Extensive experiments on three benchmark datasets show that our method outperforms most existing methods on large datasets with complex patterns. The code will be published at the following link: Anomaly-detection-guided-by-clustering-learning

Bionic dual-scale structured films for efficient passive radiative cooling accompanied by robust durability.

Passive radiative cooling (PRC), as an energy-free cooling approach, is ingeniously harnessed for certain natural organisms to withstand extreme high-temperature climates, which has inspired numerous bionic designs. However, it is a great challenge to enhance the durability of the designed materials in practical scenarios while inheriting the natural biological principles. We demonstrate bionic dual-scale structured (BDSS) films for efficient passive radiative cooling accompanied by robust durability after discovering the excellent thermoregulatory properties of the inner surface of Hawaiian scallop shell. We found that the inner surface of the shell consists of large-scale triangular ridges scattered with small-scale terrace steps. This dual-scale structure can enhance the reflectivity of sunlight by efficient Mie scattering and increase the emissivity in the mid-infrared range by lengthening the propagation of photons, thereby decreasing the surface temperature. Underpinned by this finding, we developed a BDSS film that features a strong solar spectrum reflectivity of 0.95 and a high mid-infrared emissivity of 0.98, achieving a sub-ambient cooling of 10.8 °C under direct sunlight. Additionally, the designed films possess robust durability including excellent self-cleaning, flexibility, mechanical strength, chemical stability, and anti-ultraviolet radiation, which is promising for thermal thermoregulation in various harsh scenarios.

Laser Perforated Dual-Scale Porous Electrodes Considering the Interdigitated Flow Field for Vanadium Redox Flow Battery

The conflict between the specific surface area and hydraulic permeability of carbon-based porous electrodes limits the further improvement of redox flow battery (RFB) system performance. Dual-scale electrode design is a feasible approach to overcome this contradiction. In this study, we prepared dual-scale electrodes by perforating graphite felts using an infrared laser. Based on the symmetry of the interdigitated flow field structure, we proposed three dual-scale structure designs with different combinations of large and small pores and tested their performance on a vanadium redox flow battery (VRFB) single cell. The results showed that the design with perforations under the center of the rib could increase the maximum power density by approximately 2.4 times compared to the original electrode. Furthermore, to investigate the effect of the large pores formed by laser perforation on the local electrolyte velocity, active species concentration, and reaction rate distribution, we proposed a pore-network model and investigated the influence of different combinations of large and small pores and different operating conditions on overall performance through numerical simulation. The results showed that the optimal combination of large and small pores is related to the flow rate and other operating conditions, and that setting large pores under the rib near the outlet channel is expected to provide more performance gains in VRFBs equipped with interdigitated flow fields under typical operating flow rates.

Controllable multi-scale hydrophobic structures on titanium alloy by polarization-dependent femtosecond laser fabrication and magnetron sputtering

A significant challenge is to develop effective and controllable processes for fabricating hydrophobic metal surfaces with high mechanical properties. The combination of femtosecond laser direct writing (LDW) and gold nanoparticle magnetron sputtering (Au-MS) has successfully produced multiscale structures on Ti–6Al–4V (TC4) alloy, which possess excellent superhydrophobic and hardening properties. By adjusting the laser polarization to control micro/nanostructures, the dual-scale structure is transformed into a triple-scale structure, leading to a significant increase in the contact angle under proper scanning intervals. The Au-MS further fabricates a superhydrophobic surface, with a maximum contact angle of 153° and a minimum sliding angle of 4°. Surface hardness can be raised to 408 HV from 367 HV. This work reveals that the wetting mechanism for the dual-scale structures of TC4 alloy fabricated by laser direct writing is in the Cassie-Baxter state. While the triple-scale structures of Au-MS after linear polarization LDW (LPLDW) and the triple-scale structures of circular polarization LDW (CPLDW) with or without Au-MS are in Wenzel state, resulting in a different relationship between contact angle and surface structure. The flexible and high-efficiency fabrication of these multiscale structures has made TC4 alloy more competitive in self-cleaning and anti-freezing applications.

Regulation of dual-scale structure of polypropylene/poly(ethylene-co-vinyl alcohol) hollow fiber membranes with bimodal pore base on lamellae optimization during annealing

Solvent-free manufacturing process of high performance polymer hollow fiber membranes has always been a desirable direction. Therefore, maleic anhydride grafted polypropylene (PP-g-MAH) as compatibilize, the polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes (PMEHFMs) with bimodal pore were manufactured via melt-spinning and stretching. Bimodal pore structure was constructed for improving the porosity and retaining the rejection performance. Based on the effect of EVOH on nucleation behavior and crystal growth of PP phase, the effect of annealing temperature on microscopic lamellar structure of hollow fibers with adding EVOH was investigated in detail, and the results were expected to guide the regulation of dual-scale structure of bimodal pore. With rising annealing temperature, long period of crystal (L) gradually increased, but thickness of lamellae (Lc) and rigid amorphous (Ltr) firstly increased and then decreased when annealing temperature increased to 160 °C, and optimum values were obtained when annealing temperature was 150 °C. The optimum crystallinity and lamellar orientation of annealed hollow fiber annealed at 150 °C were 48.48% and 0.863, respectively. As the annealing temperature increased, the most probable pore size of small scale pores in PMEHFMs increased firstly and then stabilized at 183 nm, which was correspond to the change of lamellar thickness in annealed hollow fibers. Whereas, the most probable pore size of large scale pores did not show a significant change trend. The porosity increased firstly and then decreased with the increase of annealing temperature, which was also correspond to the change of pure water fluxes of PMEHFMs. The porosity and pure water flux of PMEHFM reached the maximum when the annealing temperature was 150 °C.

Study on Nonfluorinated Preparation and Properties of Superhydrophobic Surface

The preparation of a superhydrophobic surface on metal can improve the self-cleaning, anti-fouling, and anti-bacterial properties of the surface. At present, the superhydrophobicity of the sample surface is mostly obtained by modifying the rough surface with fluorine-containing modifiers, which is unfavorable to the environment. Therefore, developing superhydrophobic surfaces without environmental pollution has become a research hotspot. Based on laser etching technology, the rough surface with a micro-nano dual-scale structure was prepared on aluminum alloy, and then a green and natural saturated fatty acid — myristic acid was used to modify the rough surface. Contact angle measuring instrument, depth of field microscope, scanning electron microscope and Fourier transform infrared spectrometer were used to characterize the wettability, surface morphology, and chemical composition of the modified rough surface (S1). Self-cleaning, anti-contamination, antibacterial, mechanical durability, and thermal stability of the S1 surface were tested experimentally. The wetting of droplets on hydrophobic surface was simulated by using COMSOL Multiphysics software, and a computational model was established to compare different functional structures, so as to understand the influence of parameters on the enhancement of hydrophobic properties of material surface. The results showed that the static contact angle (WCA) of the surface modified by myristic acid reached 152.3[Formula: see text], and the hydrophobic index was −0.808, and the WCA value first increased and then decreased with the change of modification time and concentration. With the increase of myristic acid concentration, the peak value of the contact angle WCA of S1 was negatively correlated with modification time. The self-cleaning rate, anti-stain rate, and antibacterial rate of S1 were 91.4%, 83.6% and 88.4%, respectively, showing excellent self-cleaning, anti-stain, and antibacterial ability. In the mechanical durability test, the S1 surface can resist at least 50 times tape peeling, 30 times steel wool friction and wear, the and 180[Formula: see text]g sand falling impact test still keeps superhydrophobic. In the thermal stability test, the S1 surface remains superhydrophobic after heat treatment at 100–200[Formula: see text]C for 30[Formula: see text]h. In this study, the multifunctional superhydrophobic surface was obtained on aluminum alloy by laser etching technology combined with a green fluorine-free modifier, which provided some meaningful ideas and references for the green preparation of superhydrophobic surfaces and the application and development of superhydrophobic surfaces in biomedical metals.

Enhancing properties of Li2TiO3/Li4SiO4 tritium breeding ceramics by chitosan addition

Li2TiO3/Li4SiO4 ceramics have been regarded as promising tritium breeders due to their numerous merits. In this work, chitosan was employed as an effective binder to provide adhesion of Li2TiO3 particles to Li4SiO4 particles, resulting in Li2TiO3/Li4SiO4 ceramics with improved performance. Chitosan could be removed during the sintering process and had little influence on the phase composition. The resulting Li2TiO3/Li4SiO4 ceramics had higher density (92.5%T.D.), greater crushing loads (115.2 ± 20.8 N) and superior thermal properties (3.61 W/m∙K) when compared to the samples prepared without chitosan. SEM analyses displayed a dual-scale structure and the inter- and trans-granular fracture mode. Thermal cycling tests revealed that the phase composition was stable but the crushing load fell slightly. The crushing load remained at 92.4 ± 17.1 N after 12 cycles. Overall, chitosan plays an important role in the amelioration of interface combination between Li4SiO4 and Li2TiO3, and thus significantly improve density, crushing load and thermal conductivity of Li2TiO3/Li4SiO4.

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.

Selective liquid directional steering enabled by dual-scale reentrant ratchets

Achieving well-controlled directional steering of liquids is of great significance for both fundamental study and practical applications, such as microfluidics, biomedicine, and heat management. Recent advances allow liquids with different surface tensions to select their spreading directions on a same surface composed of macro ratchets with dual reentrant curvatures. Nevertheless, such intriguing directional steering function relies on 3D printed sophisticated structures and additional polishing process to eliminate the inevitable microgrooves-like surface deficiency generated from printing process, which increases the manufacturing complexity and severally hinders practical applications. Herein, we developed a simplified dual-scale structure that enables directional liquid steering via a straightforward 3D printing process without the need of any physical and chemical post-treatment. The dual-scale structure consists of macroscale tilt ratchet equipped with a reentrant tip and microscale grooves that decorated on the whole surface along a specific orientation. Distinct from conventional design requiring the elimination of microgrooves-like surface deficiency, we demonstrated that the microgrooves of dual-scale structure play a key role in delaying or promoting the local flow of liquids, tuning of which could even enable liquids select different spreading pathways. This study provides a new insight for developing surfaces with tunable multi-scale structures, and also advances our fundamental understanding of the interaction between liquid spreading dynamics and surface topography.

Construction of superhydrophobic surfaces via dual-scale modified particles and digital light processing 3D printing techniques

This article reports a method of Construction of superhydrophobic surfaces via digital light processing (DLP) and a low-cost, clean, and non-fluoride calcium sulfate particle (CSP) modification method with stearyl chloride. Modified micron-scale CSP and nano-scale hydrophobic fumed silica (HFS) were added into photocurable resin as fillers to prepare 3D printing ink. Relying on the manufacturing features of DLP 3D printing layer-by-layer curing and layer-by-layer stacking. The nano-scale HFS and micro-scale CSP are uniformly assembled to the surface and form a superhydrophobic layer with a dual-scale structure, so 3D objects with superhydrophobic surfaces were successfully prepared. The contact angle (CA) of superhydrophobic surfaces reached 157°, and the sliding angle (SA) reached 2.64°. Relying on the advantages of high precision of DLP 3D printing technology, different 3D samples were printed, whose surfaces also exhibited excellent superhydrophobic, which makes 3D objects expected to be applied in the fields of liquid transportation, micro-reactor, etc.

Superhydrophobicity mechanism of refoliated quaking aspen leaves after complete defoliation by LDD (gypsy, spongy) moth caterpillars

Complete defoliation of trees due to periodic LDD (Lymantria dispar dispar) moth outbreaks in many parts of the world is a significant stress factor for the survival of individual trees and entire forests over vast areas. This study addresses such a mid-summer defoliation event in Ontario, Canada for quaking aspen trees during 2021. It is shown that complete refoliation in the same year is possible for these trees, albeit with significantly smaller leaf size. Regrown leaves showed the well-known non-wetting behaviour typically observed for the quaking aspen tree without a defoliation event. These leaves have the same hierarchical dual-scale surface structure consisting of nanometre-size epicuticular wax (ECW) crystals superimposed on micrometre-sized papillae. This structure provides for the Cassie-Baxter non-wetting state with a very high water contact angle on the adaxial surface of the leaves. Subtle differences in the leaf surface morphology of the refoliation leaves compared with the regular growth leaves are likely due to environmental factors such as seasonal temperature during the leaf growth period after budbreak.

Micro/nano dual-scale porous surface structure of the Al alloys and improvement on the joint strength with carbon fiber reinforced PA 6 thermoplastic

Improving the interfacial bonding strength of the Al/CFRTP hybrid composites is beneficial for its application in lightweight automotive technology. This study fabricated the micro/nano dual-scale porous surface structures of the Al alloy by the low-cost and effective oxalic acid anodizing to improve the interlocking interface structure. The effects of current density and oxidation time of the anodic oxidation on the shear strength of the Al/PA 6 CFRTP hybrid composite joints were investigated. The results showed that with the increase of the oxidation current density and time, the nanopore diameter, porosity, wettability, and oxide film thickness were significantly improved. The shear strength of the Al/CFRTP PA 6 joints was as high as 23.7 MPa. The micro-scale pits (average size 6 μm) produced by the NaOH treatment and the nano-scale porous structure (16–106 nm) induced by anodizing enhanced the adhesion area and anchoring effect between the Al alloy and PA 6 resin. Thus, the synergistic improvement in the interfacial bonding strength was exhibited.