Effect Of Surface Microstructure Research Articles

Effect of Photolithographic Biomimetic Surface Microstructure on Wettability and Droplet Evaporation Process.

In nature, engineering technology and daily life, wetting phenomena are widespread and have essential roles and significance. Bionics is becoming increasingly important nowadays and exploring the mechanism that influences biomimetic surface microstructure on droplet wetting process and heat and mass transfer characteristics is becoming more meaningful. In this paper, based on photolithography technology, SU-8 photoresist was used as raw material to prepare biomimetic surfaces with microstructures in various arrangements. The research results show that the wettability of biomimetic functional surfaces can be regulated by regulating the shape and arrangement of photoresist micro-pillars. At the same time, the effects of surface microstructure configuration and roughness on the heat and mass transfer processes within the droplets were also comprehensively studied. The results show that a biomimetic surface with cylindrical micro-pillars can effectively inhibit the evaporative cooling effect of the liquid-vapour interface. This effect becomes more evident with the increase in roughness, and the interface temperature difference can be reduced by up to 18%. Similarly, the biomimetic surface with cylindrical micro-pillars can also effectively promote the evaporation rate of sessile droplets, which can be increased by about 13%. In addition, the research also shows that regardless of the structure, substrate temperature changes will significantly impact the wetting phenomenon of the biomimetic surface. This study aims to guide the optimal design of biomimetic surfaces prepared based on photoresistance.

Insight into the synergistic effects of surface microstructures and wall peristalsis on glucose production in a bionic microreactor

The enzymatic hydrolysis stage is regarded as a key step in the production of biofuels derived from lignocellulosic biomass, but the elevated production expenses and limited conversion efficiency are still not favorable for practical applications. In this study, inspired by the efficient degradation of cellulose in the termite gut, a cellulase-loaded flexible microreactor model with bionic surface structures was first proposed for the production of fermentable glucose. In such a system, the fold-like structures can provide more enzyme loading sites, and villus-like structures can not only increase enzyme loading but also improve radial transfer in the microreactor. These two structures synergized well and resulted in a 58.5% increase in glucose production compared to the control. Applying peristalsis can further enhance mass transfer by the formation of backflow and vortex, and reducing the peristaltic period is more effective than increasing the peristaltic amplitude for glucose production enhancement. The glucose concentration obtained by the synergistic enhancement of peristalsis and surface structure was 2.3 times of the control. Moreover, for reactions with higher intrinsic reaction rates, the system is in a mass transfer-limited state and peristaltic enhancement is more effective. These results give insight into the design of the bionic flexible microreactor for efficient glucose production.

Effect of surface microstructure for corrosion resistance and magnetic properties of an amorphous cobalt-based Co-Si-Fe-Cr-Al ALLOY

The surface of an amorphous cobalt-based alloy of nominal composition Co75Si15Fe5Cr4.5Al0.5 was modified by nanostructures at anodizing in an ionic liquid – bis(trifluoromethane sulfonyl)imide 1-butyl-3-methyl- imidazolium. The magnetic (saturation specific magnetization and coercive force) and corrosion (corrosion potential and resistance) characteristics of an amorphous alloy before and after electrochemical modification of the surface by nanostructures are compared. Modification of the alloy surface partially changes its magnetic properties. After corrosion tests, an increase in the value of coercive force is observed. Corrosion tests were carried out by the method of polarization curves in Ringer’s solution. The corrosion resistance of alloys modified by oxide nanostructures is higher than the corrosion resistance of a polished alloy. The increase in corrosion resistance is mainly determined by the presence of nanostructures.

Secondary roughness effect of surface microstructures on secondary electron emission and multipactor threshold for PTFE-filled and PI-filled single ridge waveguides

Secondary electron yield (SEY) is a dominant factor in determining the multipactor threshold. In this study, we analyzed the secondary roughness effect of surface microstructures for plastic dielectric on SEY reduction and multipactor mitigation. A single ridge waveguide (SRW) operating in Ku-band, filled with polytetrafluoroethylene (PTFE) or polyimide (PI), was designed with a dielectric–metal multipactor gap. By employing a femtosecond laser, periodic microstructures were fabricated on PTFE and PI surfaces to suppress SEY. The SEY peak values of PTFE and PI decreased from 2.05 to 1.40 and 1.37 to 1.07 by the porous surface. The surface morphologies and cross-sectional images of the porous PTFE and PI demonstrated the existence of secondary roughness structures. Via simulation, we obtained multipactor thresholds of 8496 W, 12 374 W, and 9397 W for the SRWs filled with untreated PTFE surface, ideal porous surface (without secondary roughness), and real porous surface (with secondary roughness). Similar works were implemented for the PI-filled SRWs, resulting in simulated multipactor thresholds of 7640 W, 11 327 W, and 9433 W. The results indicate that the multipactor effect may not be effectively suppressed under the influence of secondary roughness structures such as plastic velvet and foam. Besides, simulation works indicated that the radio frequency electric field could extract secondary electrons from the microstructures, weakening the mitigation effect of microstructures on multipactor. The impact of surface charging on electron motion was also analyzed by considering energy distribution. It was suggested that the surface microstructures of plastic dielectrics lead to a decrease in the surface charge density and the electrostatic field strength, weakening the self-extinguishing effect and lowering the multipactor threshold. This study provides an in-depth analysis of the effect of secondary roughness on SEY and multipactor for organic dielectrics, which makes significant sense for the further investigation of dielectric multipactor.

Analysis of water droplet motion on hydrophobic surfaces with different microstructures

AbstractThe influence of material surface microstructure on interface properties is crucial for the preparation and development of special functional materials. In this paper, polydimethylsiloxane‐based superhydrophobic surfaces of varying roughness and surface energy are prepared using the template method and a spraying technique, and the effect of surface microstructure on lateral friction is studied using a lateral friction detection system. The experimental results indicate that as the surface roughness of a sample decreases, it is observed that the water droplets transition from a Cassie state to a Wenzel state. When the roughness changes from 4.619 μm, reduce to 3.512 μm, the maximum static friction force increases from 33.59 μN increased to 51.52 μN. The lateral sliding friction force ranges from 15.87 ± 1.9 μN increases to 40.91 ± 1.2 μN. For a given surface roughness, when the surface energy is reduced, the water droplets on the surface can be seen to transition from a Wenzel state to a Cassie state, the maximum static friction force increases from 19.32 μN dropped to 9.23 μN, and the lateral sliding friction force increases from 15.26 ± 1.6 μN dropped to 3.47 ± 2.1 μN. However, this behavior is distinct from that observed when changing the roughness of the sample. Studying the influence of the surface microstructure on the lateral friction force observed at a solid–liquid interface can provide important insights into novel geometries that may be used in new, advanced functional surfaces.

Effect of Surface Microstructure on Joints Using Nanoporous Cu Sheet for Power Devices

Wide-bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are being developed as promising replacements for Si-based semiconductors. The operating temperature of SiC semiconductor is expected to be much higher. The replacement of soldering with new bonding process has been needed for WBG semiconductor devices. We have proposed a solid-state bonding process using nanoporous metal sheet, as a die-attach bonding method for WBG semiconductor devices. In this study, the bonding process using nanoporous Cu sheet as an insert metal was investigated to achieve a Cu disk/Cu disk bonding without solvent and flux. The shear strength of the joint using nanoporous Cu sheet at 350 and 300°C in formic acid atmosphere exceeded the shear strength of conventional Pb–5Sn solder joints which was approximately 18 MPa.

Engineering PVDF omniphobic membranes with flower-like micro-nano structures for robust membrane distillation

Conventional PVDF membranes are easily wetted and contaminated in membrane distillation (MD) process, especially when used in separating high-salinity water and oil-contained saline water. To address these issues, an omniphobic membrane was fabricated in this work. ZnO micro-flowers with a rough structure were successfully deposited onto the PVDF membrane with the assistance of polydopamine assistance. After undergoing a fluorination process, the omniphobic membranes were prepared by the synergistic effect of surface microstructure and free energy. The effects of varying Zn(NO3)2 concentrations and deposition times on morphology, pore size and separation efficiency were comprehensively examined. It was demonstrated that at a Zn(NO3)2 concentration of 50 mM and a deposition time of 0.5 h, the resulting PVDF composite membrane exhibited high liquid repellency towards all the test liquids, such as water, ethanol solution, paraffin oil, and etc. Furthermore, the membrane consistently exhibited impressive salt rejection behavior (99.99%) and maintained an average flux (15.54 kg·m−2·h−1) when exposed to high-salinity solution (up to 20 wt%-NaCl). Meanwhile, during treating an oil-contained saline water emulsion with the oil content of 200 ppm, the membrane also displayed high resistance to wetting and fouling during the continuously 24 h tests. The membrane displayed a rejection rate of 99.99 % with an average vapor flux of 18.60 kg·m−2·h−1. In summary, this omniphobic membranes demonstrated a great potential in MD for practical challenging wastewater treatment.

Effect of Surface Microstructure on the Corrosion Resistance and Magnetic Properties of an Amorphous Cobalt-Based Co–Si–Fe–Cr–Al Alloy

Effect of Surface Microstructure on the Corrosion Resistance and Magnetic Properties of an Amorphous Cobalt-Based Co–Si–Fe–Cr–Al Alloy

The relationship between surface microstructure and super-lubrication performance based on 2D LDHs

The mechanism of frictional energy dissipation suggests that layered double hydroxides (LDHs) could be ideal materials for achieving solid state superlubricity due to their strong adsorption effect and weak internal interactions. In this work, three metal ion-coordinated LDHs nanosheets were designed to investigate the specific effect of surface microstructure on frictional properties. The experimental results showed that the lubrication performance is determined by the surface structure, and the friction coefficient doubles (2 × 10−3 to 3.9 × 10−3) and the adhesion force increases by 62.3% (6.9–11.2 nN) when the divalent metal ions change from tetrahedral to octahedral coordination. Through crystal field stability energy analysis and density functional theory (DFT) calculations, the superlubricity of LDHs materials is attributed to two aspects: firstly, the existence of strong charge density transfer between LDHs nanosheets and the probe, known as the anchoring effect; secondly, the formation of an ultra-low sliding energy barrier interface between LDHs nanosheets and highly oriented pyrolytic graphite (HOPG). Therefore, the relationship between tribological properties and surface structure can guide future research on superlubricity materials.

Effects of surface micro-structure of fruits on droplet evaporation process: Peach and apple cases

Droplet evaporation at the fruit surface is a common issue related to the efficiency of pesticide spraying as well as freshness preservation. Many works have been carried out demonstrating the impacts of substrate characteristics on the droplet profile, wettability, and evaporation properties in the field of industrial applications. However, the influences of specific fruit skin on the droplet evaporation rate have been rarely studied. Thus, the present works aim to explore the effects of different surface micro-structures of fruits on the droplet properties experimentally through the 3D video microscope, drop shape analyzer, and infrared camera. Apple and peach have been selected respectively as two examples of waxy and hairy skins, and comparisons have been made focusing on the surface roughness, droplet profile including contact angle, contact area, and contact diameter, evaporation rate, and temperature distribution of droplets with a constant initial volume of 2ul. The results show that the differences in micro-structure for apple and peach surfaces have significant impacts on the droplet evaporation performance. A larger evaporation rate has been found for apple skin with three distinct phases including spreading, pinning, and shrinkage periods. However, the pinning phenomenon tends to be broken for the peach case due to the unique properties of super-hydrophobic surfaces and the existence of fluff. Moreover, lower values of temperature at the top center of a droplet can be always observed during the whole evaporating process with peak values of temperature gradient near the triple-phase region.

A unique, flexible, and porous pressure sensor with enhanced sensitivity and durability by synergy of surface microstructure and supercritical fluid foaming

Flexible thermoplastic polyurethane (TPU)/multi-walled carbon nanotube (MWCNT) nanocomposite piezoresistive sensor with microsphere surface and internal porous structure were prepared using a facile glass template method combining with supercritical carbon dioxide (Sc-CO2) foaming process. Effects of surface microstructure and cell structure on the piezoresistive sensing performance of TPU/MWCNT nanocomposite foam had been investigated in detail: the novel hybrid structure significantly improved the sensing performance with a fast response time (≤100 ms), a wide operating range (0 ∼ 80 kPa) and a stability of over 1000 cycles. In addition, the prepared piezoresistive sensor can be used to monitor a wide range of human physiological signals (facial activity, small arm muscle contraction and arterial pulse, etc.) due to its excellent integrated sensing performance. This work provides a route for the design of advanced piezoresistive sensors that show great potential for applications in human motion detection, artificial intelligence devices, and medical detection, etc.

Wettability of soft PLGA surfaces predicted by experimentally augmented atomistic models

A challenging topic in surface engineering is predicting the wetting properties of soft interfaces with different liquids. However, a robust computational protocol suitable for predicting wettability with molecular precision is still lacking. In this article, we propose a workflow based on molecular dynamics simulations to predict the wettability of polymer surfaces and test it against the experimental contact angle of several polar and nonpolar liquids, namely water, formamide, toluene, and hexane. The specific case study addressed here focuses on a poly(lactic-co-glycolic acid) (PLGA) flat surface, but the proposed experimental-modeling protocol may have broader fields of application. The structural properties of PLGA slabs have been modeled on the surface roughness determined with microscopy measurements, while the computed surface tensions and contact angles were validated against standardized characterization tests, reaching a discrepancy of less than 3% in the case of water. Overall, this work represents the initial step toward an integrated multiscale framework for predicting the wettability of more complex soft interfaces, which will eventually take into account the effect of surface topology at higher scales and synergically be employed with experimental characterization techniques.Impact statementControlling the wettability of surfaces has important implications for energy (e.g., self-cleaning solar panels), mechanical (e.g., enhanced heat transfer), chemical (e.g., fluids separation), and biomedical (e.g., implants biocompatibility) industries. Wetting properties arise from a combination of chemical and physical features of surfaces, which are inherently intertwined and multiscale. Therefore, tailoring wettability to target functionalities is a time-intensive process, especially if relying on a trial-and-error approach only. This becomes even more challenging with soft materials, since their surface configuration depends on the solid-liquid interactions at the molecular level and could not be defined a priori. The improved accuracy of atomistic models allows detailing how the effective properties of materials arise from their nanoscale features. In this article, we propose and validate a new molecular dynamics protocol for assessing the wettability of soft interfaces with polar and nonpolar liquids. The prediction capabilities of simulations are augmented by a close comparison with microscopy and contact angle experiments. Since smooth copolymer surfaces are considered, here the effort mainly focuses on the effect of chemical features on wettability. In perspective, the proposed atomistic in silico approach could be coupled with computational models at higher scales to include the effect of surface microstructures, eventually easing the development of multi-scale surfaces with tunable wettability.Graphical abstract

Cavitation erosion improvement following TIG surface-remelting of gray cast iron

The paper analyses the effect of the surface microstructure effects on the cavitation erosion following rapid re-melting and solidification of gray cast iron parts with lamellar graphite and perlitic matrix. The heat source used was the electric arc generated between the tungsten electrode (via the TIG process) and the gray cast iron part. The local melting of the surface was performed at different linear energy values (El = 3420–5400 J/cm) varying the current between 60 A and 90 A, at a constant voltage of 9.5–10 V. The results showed an increase of the surface hardness from 192 to 198 HV5 to 700–740 HV5 and an improvement of the cavitation erosion resistance, the mean penetration depth of the erosion decreasing by 2.4 times, and the erosion rate by 3.56 times.Optical and scanning electron microscope were used to characterize the microstructure and to identify the phases in the re-melted area. The results showed that the melting of the surface led to an almost complete dissolution of the graphite lamella; the fine microstructure after re-solidification was composed of dendrites of transformed austenite embedded in ledeburite, consisting of transformed austenite and cementite Fe3C. Austenite dendrites have a preferential orientation and martensite needles are formed inside some of them.

UV laser-produced copper micro-mesh with superhydrophobic-oleophilic surface for oil-water separation

We report a method to fabricate micro-pore arrays on a copper sheet by a 355 nm UV nanosecond pulse laser, and investigate the effects of surface microstructures and micro-pore spacing on the wettability of the formed copper micro-mesh. We found that the surface was initially hydrophilic, but changed to superhydrophobic-oleophilic with water contact angle 151° and oil contact angle about 10° after exposed to ambient environment for 14 days. We analysed the surface morphologies of the processed samples with a three-dimensional profilometer, measured the water and oil contact angles, and characterized the surface by a field emission environmental scanning electron microscope (FESEM) and energy dispersive X-ray spectrometer (EDS). The surface chemistry changes were confirmed by X-ray photographic spectroscopy (XPS). Effective oil-water separation performance of the fabricated copper mesh was demonstrated. Learning from the natural change, we designed a coating material containing C8 long C–C (H) chain and coated onto the freshly prepared copper mesh to convert the surface property into a preferred superhydrophobic-oleophilic nature. This study provides a controllable methodology consisting laser processing and surface modification for making micro-pore copper mesh as a simple and effective method for oil-water separation.

Effect of Surface Microstructure on the Hydrogen Permeation Behavior of Plasma-Nitrided AISI 4135 Steel

Hydrogen embrittlement is a serious problem for high strength steels. The reduction of hydrogen uptake by the formation of surface layers with low hydrogen diffusivity is thought to be effective in preventing hydrogen embrittlement. We reported that the plasma-nitrided surface layer composed of ε-Fe2-3N and γ’-Fe4N phases strongly inhibited hydrogen diffusion into the pure iron matrix.1) In this study, we controlled the microstructure of surface nitrided layers of an AISI 4135 steel by plasma nitriding, and investigated the hydrogen permeation behavior.AISI 4135 steel sheets of 1 mm in thickness were used as the specimens. Prior to plasma nitriding, the specimen surfaces were polished using a diamond past down to 1 μm. The plasma nitriding treatments were conducted in nitrogen-hydrogen atmospheres at 600 Pa for 3.6 ks. The temperature of the specimen surface was kept at 450 °C. Two types of nitrogen compound layers were formed on the specimen surface by changing the mixing ratio of nitrogen and hydrogen gases. One was composed of ε-Fe2-3N and γ’-Fe4N phases (specimen A), and the other was done of only γ’-Fe4N phase (specimen B). The compound layers of specimen A and B were 10 μm and 1 μm in thickness, respectively. In addition, the thicknesses of the nitrogen solid solution layers of specimen A and B were estimated to be ca. 270 μm and 210 μm, respectively.To investigate the effect of the surface microstructure on the hydrogen permeation through the specimens, the hydrogen permeation test using a conventional Devanathan-Stachurski cell was carried out. The nitrided surface was arranged in the hydrogen detection side. A Pd thin film was deposited on the specimen surfaces in the hydrogen detection side. The hydrogen detection side was polarized at 0.18 V vs. SHE in 0.1 M NaOH fully deaerated by pure Ar gas. The hydrogen entry side was polarized at −0.4 V vs. SHE in 0.1 M H2SO4. The hydrogen permeation test of specimen A reveals that the rise transient of the hydrogen permeation current was delayed and the steady state permeation current was significantly reduced. On the other hand, the hydrogen permeation behavior of specimen B was almost similar to that of the as-polished specimen. These results indicate that the nitrogen compound layer composed of ε-Fe2-3N and γ’-Fe4N phases inhibits the hydrogen permeation. Particularly, the existence of ε-Fe2-3N phase with the hcp structure is thought to be effective in preventing the hydrogen permeation.1) Y. Sugawara, I. Muto, and N. Hara, ECS Trans, 75(29), 43 (2017).

Effect of Surface Microstructure on Organic Matter Removal Ability of Microorganism-Supported Sintered Alumina Body

Effect of Surface Microstructure on Organic Matter Removal Ability of Microorganism-Supported Sintered Alumina Body

Effect of Surface Microstructure on the Heat Dissipation Performance of Heat Sinks Used in Electronic Devices.

Heat sinks are widely used in electronic devices with high heat flux. The design and build of microstructures on heat sinks has shown effectiveness in improving heat dissipation efficiency. In this paper, four kinds of treatment methods were used to make different microstructures on heat sink surfaces, and thermal radiation coating also applied onto the heat sink surfaces to improve thermal radiation. The surface roughness, thermal emissivity and heat dissipation performance with and without thermal radiation coating of the heat sinks were studied. The result shows that with an increase of surface roughness, the thermal emissivity can increase up to 2.5 times. With thermal radiation coating on a surface with microstructures, the heat dissipation was further improved because the heat conduction at the coating and heat sink interface was enhanced. Therefore, surface treatment can improve the heat dissipation performance of the heat sink significantly by enhancing the thermal convection, radiation and conduction.

Photocatalytic Superamphiphobic Coatings and the Effect of Surface Microstructures on Superamphiphobicity.

In recent years, superamphiphobic coatings have been widely used in industrial transportation and environmental treatments because of their unique liquid repellency. In this study, WO3-TiO2 nanorods/SiO2 were used as the constructor of surface microstructures, and 1H,1H,2H,2H-perfluorodecyltriethoxysilane was used as the provider of low surface energy, and a photocatalytic superamphiphobic coating (FTS coating) was prepared. The microstructure and chemical composition of the coating was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The coating exhibited excellent photocatalytic activity toward degradation methyl red and nitric oxide (NO), and the degradation efficiency to NO reached 47.8%. Also, the advanced contact angle and the hysteresis angle of water, glycol, glycerol, and olive oil was used to evaluate the superamphiphobicity. After 7 days of ultraviolet (UV) aging, five cycles of airbrush flushing and 48 h of immersion in acid, salt, and alkali solutions, the FTS coating still exhibits excellent amphiphobicity, which lays a foundation for its large-scale applications in the concrete exterior wall. The surface microstructure and the formation of air pockets are a prerequisite for superamphiphobicity, which promotes the liquid on the coating surface into the Cassie-Baxter state. Furthermore, the formation of air pockets is closely related to the gas adsorption capacity and the specific surface area (SBET) of the surface microstructure on the coating surface. The coatings with different SBET constructed and the advanced contact angle were measured. The influence of air pockets on the superamphiphobicity of coatings was studied in combination with the optical microscope. The understanding that SBET further influences superamphiphobicity by affecting the surface air pockets is proposed.

Lithium stripping: anisotropic evolution and faceting of pits revealed byoperando3-D microscopy

Operando3-D microscopy of individual pits during Li metal anode stripping demonstrates anisotropic expansion, edge faceting, and surface microstructure effects.

Progress in Effects of Microenvironment of Carbon‐based Catalysts on Hydrodeoxygenation of Biomass

AbstractCarbon‐based catalysts have made significant progress in hydrodeoxygenation (HDO) of biomass. Since the HDO reaction usually carried on surface of catalyst, the interaction of reactant with catalyst is closely related to the surface microenvironment of catalyst, which may further have an impact on catalytic performance. This review will discuss the relationship between surface microenvironment of carbon support and catalytic performance and mechanism of HDO reaction during biomass upgrading. We will focus on the microenvironment effect associated with HDO reaction in carbon‐based catalysts including effects of surface microstructure and surface functionalization of carbon supports on preparation of heterogeneous catalysts and catalytic performance, respectively. Study of microenvironment may provide guidance for further development of efficient carbon‐based catalysts in biomass resource utilization.