V-shaped Microgrooves Research Articles

Effects of surface nanotexturing on the wickability of microtextured metal surfaces

Hypothesis: Achieving spontaneous, rapid, and long-distance liquid transport is crucial for many practical applications such as phase change heat transfer and reactions at solid–liquid interfaces. Surface nanotexturing has been widely reported to improve the wickability of microtextured metal surfaces. Although surface nanotextures show high capillary pressure, the high fluid flow resistance through nanotextures prevents fluid transport. The underlying mechanisms responsible for the enhanced wickability of nanotextured surfaces are still unclear.Experiments: Herein, we prepared a variety of microtextures and nanotextures on copper surfaces by femtosecond laser micromachining and chemical oxidation, respectively. The wickability of these textured surfaces was quantitively compared by measuring wicking coefficient and capillary rise speed. We designed experiments to eliminate any possible effects of surface oxidation and metal composition on wickability. A theoretical model describing the vertical and horizontal capillary flow in V-shaped microgrooves was proposed and utilized to analyze the experimental results. The effects of time-dependent wettability on wickability were also examined.Findings: Surface nanotexturing can enhance surface wettability while altering the micrometer-scale structural characteristics. The greatly enhanced wickability of nanotextured surfaces can only be observed when the surface microtextures have a very small aspect ratio. Otherwise, for metal surfaces with fine microgrooves, the latter effect is more pronounced, and thus the surface wickability may deteriorate after preparing surface nanotextures; for surfaces with wide microgrooves, both effects are minimal, and the surface wickability enhances only marginally after surface nanotexturing. Furthermore, the wickability of microtextured surfaces will decay rapidly due to the adsorption of airborne organics, whereas adding surface nanotextures can significantly inhibit this degradation. The anti-contamination capability of surface nanotextures is considered likely to be a potential mechanism responsible for the greatly enhanced wickability of nanotextured surfaces noted in some studies.

Dual-scale porous/grooved microstructures prepared by nanosecond laser surface texturing for high-performance vapor chambers

A vapor chamber (VC) is a two-phase device used to spread heat in two dimensions, which is widely used in high heat flux applications such as the cooling of high-power chips and light-emitting diodes. The wicks inside a VC greatly affect the device performance, which is commonly prepared by sintering metal powders or fibers. Herein, we directly prepare the wick structures on copper substrates by nanosecond laser surface texturing and investigate the thermal performance of the prepared VCs. We find that both dual-scale porous structures with a porosity of ~68% and deep V-shaped microgrooves with an aspect ratio of 3.5 can be fabricated on copper substrates by nanosecond laser surface texturing. The former shows a high capillary pumping pressure and the latter shows a high permeability. When employing the optimal structures as the wicks, the prepared 2 mm thick VC shows a minimum thermal resistance of 0.137 °C/W under a heat load of 120 W. Our results provide a novel technique to prepare wick structures used in high-performance VCs, which avoids the sintering process and may be used for the manufacturing of ultrathin VCs.

Fabrication and Characterization of CuO nanowires on V-shaped Microgroove surfaces

This study developed a facile and scalable thermal oxidation method to prepare CuO nanowires on the electro-discharge machining (EDM) processed V-shaped microgrooves. The formation feasibility, surface morphology, and wetting properties of nanowires on V-shaped microgrooves were explored by the variation of thermal oxidation temperatures from 300 to 600 °C, and oxidation times from 2 h to 8 h. Nanowires were found to successfully synthesized on the V-shaped microgrooves surfaces when annealing temperature was 400 °C or higher. The microvoids or microcavities on the EDM processed V-shaped microgrooves surfaces contributed to the stress grain boundary (GB) diffusion of copper atoms, and facilitated the growth of nanowires. The diameter of nanowires increased monotonically when the annealing temperatures increased, whereas it almost kept unchanged with increasing annealing times. The length of nanowires was influenced positively by both annealing temperature and annealing time. All the nanowire samples showed hydrophobic properties of water.

Formation of Bottom Conjugate Pair Grooves by Femtosecond Laser Grooving on Transparent Substrate

Ultrashort pulsed laser is a promising tool for processing transparent materials. We report on a new approach that simultaneously creates a pair of conjugate grooves on the bottom surface of a thin glass substrate at the duration of plowing a V-shaped microgroove on the top surface using the technique of direct laser ablation. We propose a hypothesis to explain the accompanying grooves’ formation mechanism and simulate Maxwell’s equations to verify its applicability. Measurements showed the surface roughness of the groove’s sidewalls was 0.14 $\mu \text{m}$ . This method requires no mask, can be directly performed in the atmosphere, and can simultaneously produce microgrooves on both sides of the substrate that render it an effective approach for producing high quality V-shaped microgrooves on both sides of the substrate.

The effect of femtosecond laser fluence and pitches between V-shaped microgrooves on the dynamics of capillary flow

Open microgroove is one kind of capillary-driven superwicking surface structure. In this study, arrays of parallel V-shaped microgrooves were fabricated on an aluminum surface by using a femtosecond laser to obtain a superwicking surface which can quickly transport the water uphill against gravity. The relationships between the flowing time and flowing distance were investigated and compared with theoretical results. We demonstrated both laser fluence and scanning step size can affect the superwicking performance. The aluminum surfaces fabricated at a laser fluence of 18.49 J/cm2 and 52.67 J/cm2 showed the best superwicking performances with the average water flow velocities approximately 16.2 mm/s and 16.4 mm/s, respectively, in the distance of 30 mm. On the other hand, the superwicking surfaces show an anisotropic flow characteristic due to the parallel microgrooves structure. However, when the scanning step size drops to 25 µm, the surface will form irregular rough structures that result in the isotropic flow characteristics. Moreover, by using a thermal camera, we found that after a 10 µL water droplet was dropped into the heated surface, the superwicking surface temperature quickly dropped from 92.4 °C to 82.5 °C which indicated that laser processing of the superwicking surface has potential application in heat dissipation.

Fast water flow in laser micromachined microgrooves with nonuniform surface wettability

Fast water flow on solid surfaces is desired in many applications. In this paper, surfaces with microgrooves and nonuniform wettability were fabricated, and fast water flow with an average velocity of 47.6 mm/s was achieved. The proposed method included three steps: fabricating V-shaped microgrooves on copper surfaces by a pulsed laser, storing laser-processed samples in an organic-rich vacuum environment and partially soaking the samples in H2O2 solution. The morphology and composition changes during the three steps were analyzed using SEM, 3D laser microscopy, XRD, XPS and EDS, and the water flow on various surfaces was studied. Our results indicated that the presence of a suitable wettability difference at the front edge of a superhydrophilic surface can accelerate water flow on the surface. Our results may provide new ideas for the fabrication of high-performance heat pipe or water harvesting surfaces.

Elongated Bouncing and Reduced Contact Time of a Drop in the Janus State

Fast drop bouncing is desired in numerous applications. However, it has never been realized on a superheated surface with concurrent contact boiling and the Leidenfrost effect (the so-called Janus thermal state). This is presumably because of the increased drop adhesion as a result of bubbling on a Janus surface. Nevertheless, on a hydrophilic SiN x surface with v-shaped Si microgrooves in this thermal state, an elongated bouncing for a water drop was observed and a small drop contact time of 10.36 ms was obtained. We propose that the elongated bouncing was originated from an asymmetric momentum force created by the vapor bubbles at the rim of the drop. Analytical expressions for the contact time and the asymmetric momentum force were established and the predictions qualitatively agreed with the experimental results. The obtained contact time was the lowest value that has ever been reported in the Janus thermal state. The proposed approach has promising applications in state-of-the-art technologies requiring high liquid mobility.

Direct writing of large-area micro/nano-structural arrays on single crystalline germanium substrates using femtosecond lasers

A direct writing technique for fabricating micro/nano-structural arrays without using a multi-scanning process, multi-beam interference, or any assisted microlens arrays is reported. Various sub-wavelength micro/nano-structural arrays have been directly written on single crystalline germanium substrate surfaces using femtosecond laser pulses. The evolution of the multiscale surface morphology from periodic micro/nano-structures to V-shaped microgrooves has been achieved, and the relationship between array characteristics and laser polarization directions has been discussed. The self-organization model agrees well with the experimental results in this study.

Biomimetic optimization research on wind noise reduction of an asymmetric cross-section bar.

Background In this paper, we used the principle of biomimetics to design two-dimensional and three-dimensional bar sections, and used computational fluid dynamics software to numerically simulate and analyse the aerodynamic noise, to reduce drag and noise.Methods We used the principle of biomimetics to design the cross-section of a bar. An owl wing shape was used for the initial design of the section geometry; then the feathered form of an owl wing, the v-shaped micro-grooves of a shark’s skin, the tubercles of a humpback whale’s flipper, and the stripy surface of a scallop’s shell were used to inspire surface features, added to the initial section and three-dimensional shape.ResultsThrough computational aeroacoustic simulations, we obtained the aerodynamic characteristics and the noise levels of the models. These biomimetic models dramatically decreased noise levels.

Forming mechanism of radial V-shaped microgrooves on plate using step punching method

The finned surface can increase the specific surface area, which could enhance the boiling efficiency of the working medium to realize the enhancement of heat transfer performance. This research adopted a step punching method to form a radial microgroove structure on the surface of a copper plate. The scanning electron microscopy analysis indicates that when the pressed metal is in the deformation range, it will flow under extrusion and is subject to the reaction force from the metal outside the deformation range, so a micro-finned structure nearby the punching tool is formed. And the deformation area of the formed microgroove is higher than the workpiece’s primitive surface. The relationships of the punching interference length Li with θc, ac, and αpt are analyzed; and the influence of forming parameters on the groove surface morphology as well as the relationships among these parameters are discussed. When the punching depth ac is 0.3 mm and the punching feeding angle θc is 2°–4°, the finned surface of the radial V-shaped microgrooves can be obtained.

Phase separation micromoulding and photopatterning based on radiation induced free radical polymerisation of acrylates for the microfabrication of porous monolithic structures

Two different microfabrication techniques for the preparation of monolithic porous polymeric 3D microstructures were assessed. The first approach is based on a radiation assisted imprint process. Electron beam initiated free radical polymerisation of acrylates/methacrylates in a porogenic solvent within the confinements of V-shaped microgrooves in a silicon master enables the pattern transfer, thereby phase separation allows for the generation of a porous material of the replicate simultaneously. Furthermore, porous 3D microstructures in the format of arrays with different feature sizes in the range of 50 to 1000 micrometers were obtained by UV exposure of a liquid film of acrylates/methacrylates in a porogenic solvent through a photomask. In this paper we present the first results regarding the combined pattern transfer and polymerisation-phase separation process in the micrometer range. Microstructures and the dimension of pores and globules within these microstructures were analysed by scanning electron microscopy.

The effect of surface microgrooves and anodic oxidation on the surface characteristics of titanium and the osteogenic activity of human periodontal ligament cells

ObjectiveThe purpose of this study was to investigate the effect of titanium (Ti) surface microgrooves and anodic oxidation on the surface characteristics of titanium and the osteogenic activity of human periodontal ligament cells (PLCs) cultured on theses surfaces. DesignMechanically ground Ti was used as the control substratum (NE0). Truncated V-shaped microgrooves, 60μm-wide and 10μm-deep in cross-sections, were created on the Ti substrata by photolithography (NE60/10). Anodically oxidized Ti (NE0AO) and anodically oxidized microgrooved Ti (NE60/10AO) were also prepared. Scanning electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were performed for surface characterization. Cell proliferation assay, osteoblast differentiation assay, and quantitative real-time PCR analysis were performed to compare the osteogenic activity of PLCs on NE0, NE60/10, NEAO, and NE60/10AO. ResultsA decrease in the microgroove-width of NE60/10AO compared to NE60/10 due to Ti oxide layer generation by anodic oxidation was detected with XRD and XPS. Cell proliferation, osteoblast differentiation, and osteo-related gene expression were enhanced on the NE60/10AO substrata compared with NE0, NE60/10, and NE0AO. ConclusionsThe combination of Ti surface microgrooves and subsequent anodic oxidation treatment synergistically upregulated osteo-related gene expression, despite showing limited ability to increase cell proliferation and osteoblast differentiation levels in PLCs.

Texture direction of combined microgrooves and submicroscale topographies of titanium substrata influence adhesion, proliferation, and differentiation in human primary cells

ObjectiveThis study aimed to identify the optimal micro- and submicroscale topographies of titanium (Ti) substrata that would most significantly influence adhesion, proliferation, and other activities of these cells. DesignTruncated V-shaped microgrooves in 60μm-wide and 10μm-deep cross-sections with 0°, 30°, 60°, or 90° angles between the microgrooves and ridge-top submicroscale texture were created on the Ti substrata (designated NE60/10-0°, NE60/10-30°, NE60/10-60° and NE60/10-90°, respectively). Ground titanium with submicroscale texture but with no microgrooves was used as the control substratum, NE0. Scanning electron microscopic observation and the assays determining the cell adhesion, cell proliferation and osteoblast differentiation were performed. ResultsCells more actively migrated into the microgrooves on NE60/10-30° than into the microgrooves on any other substrata tested, suggesting that the cells utilise the increased surface area of the substrata at the microscale level. NE60/10-0° and NE60/10-30° substrata generally enhanced adhesion, proliferation, alkaline phosphatase activity, and osteoblast differentiation of human primary cells when compared to other Ti substrata, and significant correlations were observed between these cellular activities. ConclusionsHere, we show that the contact guidance of human primary cells grown on Ti substrata can be controlled more by specific submicroscale textures on ridge tops than by the dimensions of surface microgrooves only. Also, the degree of angles created between the submicroscale textures and microgrooves on Ti substrata significantly affect cell adhesion, proliferation and differentiation in human primary cells.

Development of machining technology for micropatterns with large surface area

With increasing demand for micropatterns such as V-shaped microgrooves and the trend of large surface areas in developing technologies, precision machining technology for micropatterns with large surface areas is expected to play an increasingly important role in today's manufacturing technology. In large-surface micromachining, machining time is much longer than that in general pattern machining and it is not easy to achieve uniform machining accuracy in the entire machined areas because of various factors. Therefore, systematic machining processes and technical development for achieving precision in each process are essential prerequisites to reduce the errors. In this study, we focused on developing machining technologies, which include a machine vision system for precise tool setting, an on-machine measurement system for large-area measurement, and software for tool path generation and simulation, for the fabrication of large-surface micropatterns in an electroless nickel-plated workpiece with single-crystal diamond tools and a 32-in., 675 × 450-mm mold with tens of V-and pyramid-shaped micropatterns.

Experimental investigation of enhanced spreading and cooling from a microgrooved surface

A heat transfer cell is specifically designed to analyze the heat spreading capacity of a microgrooved surface. V-shaped microgrooves are etched on silicon wafers using standard lithographic process. The shapes of the liquid menisci in the microgrooves are accurately measured using image analyzing interferometry as functions of heat input and opposing body force (angle of inclination). The relevant parameters that govern the spreading and cooling process of an evaporating curved microfilm, e.g., the adsorbed film thickness, contact angle, and curvature at the thicker end of the meniscus are accurately measured. The trends in these values are found to be consistent with the physics of the process. The temperature profiles are measured for the microgrooved and non-grooved silicon substrates under identical conditions of heat input and inclination and the enhanced spreading of the film in presence of microgrooves toward the hot region is quantified. The axially average values of a dimensionless temperature, defined for this study, are used to quantify the enhanced cooling and temperature homogenization potentials of microgrooved surfaces along with the effect of opposing body forces. The study clearly indicates the beneficial effects of change-of-phase heat transfer from an evaporating microfilm on microgrooved surfaces and its potential use in a miniature passive cooling device.

Creation of V-shaped microgrooves with flat-ends by 6-axis control ultraprecision machining

The use of diffractive optics having surface appearance like diffraction grating or Fresnel lens, which consist of a number of microgrooves with various shapes is analyzed. One of them is flat-end microgrooves having no slope at the end. The existence of a slope limits the design of microgrooves and causes unnecessary diffraction of light and losses. Thus, the slope must be eliminated. The study deals with the creation of curved V-shaped microgrooves with two flat-ends on a curved surface by using 6-axis control non-rotational cutting tools. The proposed method shows the effectiveness in creating flat-ended curved microgrooves on curved surfaces.

V-Shaped Microgrooving with Two Flat-Ends by 6-axis Control Machining

In recent years, attention is paid to diffractive optics which have surface appearance like diffraction grating or Fresnel lens. A variety of machining methods are requested to effectively produce metal mold of diffractive optics, consisting of a number of microgrooves with various shapes. One of them is flat-end microgrooves. Flat-end microgrooves mean microgrooves having no slope at the end. The existence of the slope limits the design of microgrooves and causes unnecessary diffraction lights and losses. Thus, the slope is requested to remove. The study deals with the creation of V-shaped microgrooves with two flat-ends by using 6-axis controll non-rotational cutting tools, that is, curved microgrooves with two flat-ends are created on a curved surface. The proposed method shows the effectiveness to create flat-end curved microgrooves on curved surfaces as well as the method of cutting edge detection to set a cutting edge symply and accurately.

Creation of Ultraprecision V-shaped Microgrooves Using Non-Rotational Cutting Tools

The study deals with the creation of ultraprecision microgrooves using non-rotational diamond cutting tools with angle of 90 degrees, which are mounted on an ultraprecision machining center. Machining experiments of micro grooves were conducted to find the optimal value of cutting speed, depth of cut, rake angle, changing the cutting speed from 1mm/min to 200mm/min, the depth of cut from 0.1m to 10m and the rake angle from -5 degrees to 30 degrees. Workpieces were machined with the cutting tool submerged in the cutting fluid to know the influence of cutting fluid supply method. From the experimental results, the adequate cutting condition is obtained such as the rake angle of 10 degrees to 20 degrees, the finish cutting speed of 1mm/min and the depth of cut in rough cut and finish cut of 1m and 0.5m respectively. As the cutting fluid supply method, workpiece submerged in the cutting fluid is effective. Using the cutting condition, fine V-shaped microgrooves are obtained in various materials. In addition, frontlight optical plate and micro Fresnel lens with the designed micro grooves were designed and manufactured by non-rotational diamond cutting method. As a result, it is also found that the non-rotational diamond cutting method enables to accurately and neatly manufacture microgrooves without any burr generation.

Effects of multigrooved surfaces on osteoblast-like cells in vitro: scanning electron microscopic observation and mRNA expression of osteopontin and osteocalcin.

This study evaluated the behavior of osteoblast-like cells on multigrooved surfaces consisting of a combination of microgrooves and macrogrooves. A polystyrene substrate was fabricated with multigrooves with 90-degree, V-shaped microgrooves with a 2-microm pitch cut on trapezoidal macrogrooves, which had a 50-microm ridge width, a 50-microm wall width, a 50-microm bottom width, and 25-microm depth. Smooth polystyrene substrates were also prepared as controls. Rat bone marrow cells were cultured as osteoblast-like cells on the substrates for morphological evaluation using a scanning electron microscope, and for biochemical evaluation using the quantitative reverse transcriptase-polymerase chain reaction technique for osteopontin and osteocalcin mRNA expression. After 8 days of incubation, the osteoblast-like cells were aligned parallel to the surface grooves on the multigrooved substrates. After 16 days of incubation, a dense mineralized extracellular matrix (ECM) was produced along the multigrooves. The ECM on the multigrooved surface appeared oriented more in the direction of the grooves than on the smooth surface, and trapezoid-shaped macrogrooves of the ECM were cast upside down. Although there were not significant differences, the osteopontin and osteocalcin mRNA expressions of the osteoblast-like cells on the multigrooved surfaces tended to be higher than on smooth surfaces. These results suggest that multigrooves could be used to control the orientation of mineralized ECM as well as of cells, and also to enhance the production of mineralized ECM.

Effects of multigrooved surfaces on fibroblast behavior.

Microgrooves have been investigated as substrates for the control of cell alignment. However, they are relatively too narrow and shallow for controlling the orientation of extracellular matrices (ECM) such as collagen. Multigrooves, a combination of microgrooves and macrogrooves, are expected to be able to control the orientation of both cells and ECM. This study investigated a method for fabricating multigrooves and evaluated fibroblast behavior on these novel surfaces. Multigrooved patterns were fabricated on a gold-alloy metal die, in which 90-degree V-shaped microgrooves with a 2-microm pitch were cut on trapezoidal macrogrooves. The macrogrooves had a 50- microm ridge width, a 50-microm wall width, a 50-microm bottom width, and a 25-microm depth. The grooves were made by an ultraprecision micromachine using a single crystal diamond. This metal die served as a template for making surface replicas from polystyrene. Microgrooved and smooth polystyrene replicas also were prepared as comparative substrates. Mouse fibroblast L929 cells were cultured in each type of replica substrate for 7 to 21 days. After these periods, the cells were fixed with 2.5% glutaraldehyde, treated with conventional methods, and, finally, observed by SEM. Confocal laser scanning microscopy was performed to investigate ECM formation. The multigrooved metal die exhibited the desired sharp configuration without defects. The dimensional values of the multigrooves on the polystyrene replicas were almost the same as the designed values. The fibroblasts on the multigrooved and microgrooved substrates were aligned parallel to the surface grooves after 7 days of incubation. In contrast to the microgrooved and flat surfaces, a dense extracellular matrix was produced along the multigrooves after 21 days of incubation. These results suggest that multigrooves can control the orientation of ECM as well as cells and thus enhance the production of ECM.