Array Surface Research Articles

Enhanced boiling heat transfer on three-dimensional hybrid micropillar array surfaces

Boiling heat transfer is widely used in numerous industrial systems because of its excellent heat dissipation performance. The critical heat flux (CHF) represents the upper limit of efficient heat removal. The most widely applied CHF model is Zuber's hydrodynamic instability model, which posits that the interference between vapor and liquid counterflows results in the CHF. In this paper, a three-dimensional (3D) hybrid micropillar array surface for hindering the liquid–vapor interface is proposed to enhance the CHF and heat transfer coefficient (HTC). The 3D hybrid surface comprises a tall hydrophobic (HB) pillar array surrounded by a short hydrophilic (HP) pillar array. The tall HB pillar array acts as a potential nucleation site for increasing the HTC, and the short HP pillar array acts as a wicking structure for facilitating liquid rewetting. In addition, the height difference between the HB and HP pillar arrays can potentially reduce the interference between liquid and vapor counterflows and increase the CHF. Relative to a plain silica surface, the 3D hybrid surface increases the CHF and HTC by 107% and 360%, respectively. Theoretical modeling suggests that the CHF on the 3D hybrid surface was still limited by pool hydrodynamics.

Highly sensitive miRNA detection of early-stage laryngeal carcinoma using a solid-state Au nanocone arrays fabricated LoC-SERS analysis system coupled with target-triggered dual cycle amplification strategy

Herein, with a target-triggered dual cycle amplification strategy, a novel lab-on-a-chip-based surface-enhanced Raman scattering (LoC-SERS) analysis system was established to analyze miRNAs quantitatively. Due to a more substantial complementary pairing effect, the presence of targets can replace the single-stranded DNA S1 (S1) from the single-stranded DNA F1 (F1) and single-stranded DNA S2 (S2) can replace and release the targets similarly. Thus, target can cyclically trigger the cycle Ⅰ and release S1 continuously. Cycle Ⅱ is the catalyzed hairpin assembly (CHA) event between the hairpin DNA 1 and hairpin DNA 2, which can connect the Ag-Au nanorods (Ag-AuNRs) to the surface of solid-state Au nanocone arrays (AuNCAs). Owing the dual cycle amplification strategy, localized surface plasmon resonance (LSPR) can be excited and significantly magnify the local electromagnetic field for SERS signal enhancement. Thus, ultrasensitive detection of miR-21 and miR-106b was achieved with the limit of detection as low as aM level. Attributed to the hydrophilic treatment and the design of capillary pump, the detection can be finished without any external pumps. Moreover, the system exhibited good practicability in the analysis of real serum samples obtained from Laryngeal carcinoma (LC) patients and healthy subjects. Therefore, the system is a promising candidate in clinical application and exhibited potential for the prediction, diagnosis, monitoring, and staging of LC.

Multivariate modeling and optimization of the reverse cationic flotation process of iron ore using depressant-modified starch

The iron ore has low quality to be directly used in steel production. Reverse cation flotation is one of the most used processes in the separation of quartz and particles smaller than 0.150 mm, and, therefore, can be used in the production of pellet feed. This project aimed at the application of modeling and optimization of flotation parameters (starch mass and time) to improve and enhance the separation and process conditions. The study of a starch-based depressant modified by different levels of temperature, starch mass, time, and mass of ammonium hydroxide, was conducted to reduce the surface tension of the water and with that, enhance the stability and formation of the nano and microbubbles. Both steps were modeled via the Central Composite Design (CCD) response surface array and the multivariate and multiobjective optimization using the Normal Boundary Intersection (NBI) algorithm. The iron concentration was 77.83 % under the optimized conditions with only 0.33 % of SiO2 content.

Analysis of Product Architectures of Pin Array Technologies for Tactile Displays

Refreshable tactile displays based on pin array technologies have a significant impact on the education of children with visual impairments, but they are prohibitively expensive. To better understand their design and the reason for the high cost, we created a database and analyzed the product architectures of 67 unique pin array technologies from literature and patents. We qualitatively coded their functional elements and analyzed the physical parts that execute the functions. Our findings highlight that pin array surfaces aim to achieve three key functions, i.e., raise and lower pins, lock pins, and create a large array. We also contribute a concise morphological chart that organises the various mechanisms for these three functions. Based on this, we discuss the reasons for the high cost and complexity of these surface haptic technologies and infer why larger displays and more affordable devices are not available. Our findings can be used to design new mechanisms for more affordable and scalable pin array display systems.

Directional Rebound of Microdroplets on a Magneto-Responsive Micropillar Array Surface.

The manipulation of droplet movement behavior is of scientific importance and has practical applications in many fields, such as biological analysis, water collection, oil-water separation, deicing, antifrosting, and so on. Using the magneto-responsive surface to dynamically change the surface morphology is an effective method to realize droplet manipulation. A replica molding technique was used to fabricate the surface with the magneto-responsive micropillar array, and the direction of the micropillar array could be changed dynamically with the magnetic induction intensity. The mechanism of the droplet directional rebound on the magneto-responsive surface and the implementation of the controllability of droplet movement were investigated. On the magneto-responsive surface, it was achievable to realize the directional rebound of droplets on the micrometer scale. The critical condition for the droplet directional rebound was identified. The force and energy of the droplet during the spreading and retraction stages were analyzed, which lay a theoretical foundation for the precise control of droplet directional rebound.

Fabrication of TiO2/CdS/Co(OH)2 composite and its application in photoelectrochemical cathodic protection of 304 stainless steel under visible light

CdS quantum dots (QDs) and Co(OH)2 were deposited on the surface of TiO2 nanotube arrays (NTAs) by successive ionic layer adsorption and reaction (SILAR), and the performance of the composite in photoelectrochemical (PEC) cathodic protection was studied. Due to the narrow band gap of CdS QDs and the formation of type II heterojunction with TiO2, the TiO2/CdS (Ti/Cd) composite exhibited enhanced PEC properties in 3.5 wt% NaCl solution. After deposition of Co(OH)2, the valence conversion of Co(II) and Co(III) improves the separation efficiency of charge carriers, the cathodic protection performance of TiO2/CdS/Co(OH)2 (Ti/Cd/Co) composite is further improved.

Amoeboid soft robot based on multi-material composite 3D printing technology

A core–shell structured, amoeba-like, magnetically controlled soft robot is proposed for 3D printing using magnetically controlled smart materials and silicone materials. The purpose of this robot is to overcome the limitations of existing soft robot kinematic mechanisms that rely on the elastic deformation of flexible materials. The printability of the magnetically controlled smart material was verified through rheological tests. The effect of different component ratios on the rheological properties of the material was investigated and a suitable material ratio for printing was selected by adjusting the amount of SiO2 in the silicone and conducting rheological tests. Mechanical simulation was used to select and optimize the design of the amoeboid soft robotic shell structures. Printing was then used to verify the stability of the shell structures. The self-supporting capability of the magnetically controlled smart materials was investigated under different magnetic field strengths. To solve the problem of the phase of the magnetron smart material and the silicone material, the composite printing of the two materials was accomplished by adjusting the printing process. Soft robots mimicking amoebas were then printed and fabricated. The magnetron array-based driving method is proposed, and the magnetic field of the array used to drive the amoeba-like soft robot is constructed. The magnetic field of the array surface was then simulated under several different driving modes. Based on the simulation results, a suitable driving mode was selected. Using the material mechanism of the magnetron-only material sol–gel transformation, the pseudopod extension gait of the amoeba-like soft robot was designed, and the localized deformation of the amoeba-like soft robot was realized.This paper leveraged the distinctive properties of magnetorheological smart materials to devise and fabricate an integrated 3D-printed soft robot. Such magnetorheological smart materials can function as both the supporting framework for hollow cavities and the propelling substance for the robot. During the course of this process, we investigated material properties pertinent to 3D printing and refined the design of the robot's structure and driving mechanism.

Self-supported iridium integrated leaf-shaped Fe3O4 columnar arrays toward highly efficient oxygen evolution at industrial-grade current density

The sluggish kinetics for oxygen evolution reaction (OER) significantly impede the practical applications of electrocatalytic water splitting technology for renewable energy source. The facile design of self-supporting electrocatalysts with high activity and stability for OER catalysis at industrial-grade current density is of paramount significance to mitigate the above bottlenecks. We report herein the construction of iron foam (IF) self-supported Ir-magnetite (Ir-Fe3O4/IF-T-x) electrode via galvanic replacement between IrCl62− ions and Fe2+ in Fe3O4 nanosheet arrays, which is simply synthesized by annealing IF in air and subsequent thermal treatment in reducing atmosphere. Such pre-treatment enables the growth of leaf-like Fe3O4 nanosheet arrays with rich Fe2+ species and oxygen defects, which facilitate the depositing of Ir on the surface of nanosheet arrays and thereby promote the electrochemical OER performance in basic electrolyte. Impressively, the optimized Ir-Fe3O4/IF-400-2 delivers the highest electrocatalytic activity with a low overpotential of 316 mV to obtain industrial-grade current density of 500 mA cm−2 for alkaline OER. Meanwhile, the catalyst still shows good long-term stability after 36 h V-t test at 100 mA cm−2. This study offers a simple and efficient pathway to prepare self-supporting electrode for alkaline OER at industrial-grade current density.

Improved geoelectrical resistivity monitoring for earthquake precursors near the Xinfengjiang reservoir of southern China, with a fixed Wenner array of downhole electrodes in four separated boreholes

Over the past five decades, a geoelectrical resistivity monitoring experiment using fixed electrode arrays has been conducted at Heyuan in the Guangdong Province of China for detecting possible earthquake precursors near the Xinfengjiang reservoir. A pair of surface quasi-Wenner arrays designed to monitor temporal resistivity variations have been used in two oblique directions of N27°E and N80°W with electrode spacings AB/MN of 997 m/315 m and 1032 m/328 m, respectively. To reduce the effects of near-surface environmental changes, an improved experiment has been introduced in August 1992, using a subsurface Wenner array in the direction of N80°W with electrode spacings AB/MN of 54 m/18 m, consisting of downhole electrodes in four horizontally separated boreholes at the same depth of 65 m. During the experimental period of August 1992 to December 1996, a continuously downward trend in apparent resistivity with the improved downhole array and a peculiar annual variation with the conventional surface arrays have been observed. For the same period, no notable earthquakes occur in and around the Xinfengjiang reservoir. The field tests indicate that the downward trend of apparent resistivity was due to the aging of one of the current electrodes. By using simple layered models, we develop a sensitivity analysis to design a monitoring array with minimum environmental effects and to explain the observed resistivity variations, such as a paradoxical resistivity behavior related with negative sensitivity. No significant resistivity variations, which could be attributed to earthquake activity of magnitude 3.4 or less in the study area, are detected. We prove that the two monitoring methods with the modified subsurface Wenner and the conventional surface quasi-Wenner arrangements can complement each other to efficiently estimate a change in the electrical properties of rocks and reduce the ambiguity in the interpretation of apparent resistivity data.

Array structure of monocrystalline silicon surface processed by femtosecond laser machining assisted with anisotropic chemical etching

Monocrystalline silicon (m-Si) with array structure has excellent optical and surface properties in the application of solar cells and optoelectronics. However, due to its hard and brittle properties, the efficient and high-quality micro-processing of complex array structured m-Si surface is difficult. In this work, micron array structure, such as inverted pyramid (IP) array structure, V-shaped groove array structure, and positive pyramid array structure, was generated on the m-Si surface by an efficient femtosecond laser machining assisted with anisotropic chemical etching. The morphology changes of microholes during the etching process, as well as the surface and optical properties of array structured m-Si, have also been studied. Experimental results showed that V-shaped groove array structure m-Si achieved superhydrophilic performance. The m-Si of IP array structure and V-shaped groove array structure exhibit high absorptivity (>95 %) and low light reflectivity (<5%) within a wide spectral range from 400 to 950 nm. This study reveals that femtosecond laser machining assisted with anisotropic chemical etching is a facile and feasible avenue to produce array structured m-Si with excellent optical performance.

Experimental investigation and correlation analysis of pool boiling heat transfer on the array surfaces with micro-fins using FC-72 for the electronic thermal management

Pool boiling heat transfer characteristics were investigated on the both homogeneous and fractal array micro-pin-finned surfaces using FC-72 as working fluid. Two distinct fractal geometry pattern surfaces (Array4 and Array9) were designed to further explore their boiling heat transfer performance. The effect of different subcoolings (0 K, 15 K and 25 K) has also been analyzed combining fractal array surfaces. Bubble dynamics were captured using a high-speed camera. The results present the the array micro-pin-finned surfaces with less heat transfer area ratio can achieve similar or even higher CHF compared to the uniform micro-pin-finned surface (PF0.3–0.2–2), especially for subcooled boiling (ΔTsub = 25 K). Notably, bubbles nucleate and grow prior to reaching the micro-pin-finned unit region. This phenomenon is evident in visual images, indicating that the fractal array effectively impedes bubble coalescence, particularly during subcooled boiling. Besides, this fractal array surface can provide liquid supply channels and prevent dry-out. The mechanism behind the heat transfer enhancement and CHF triggering is elucidated based on liquid replenishment and bubble coalescence behaviors. A CHF prediction model was established considering the effect of liquid subcooling, rectangular array distribution, and micro-fins feature size. And the prediction results from this model show well agreement with experimental values and data points from literature, with mean absolute deviation being less than ± 15 %.

Fast tool servo-based ultra-precision diamond sculpturing for fabricating micro-structured surfaces

To eliminate differences in surface quality and improve the machining flexibility of micro-structured surfaces, this paper proposes a novel ultra-precision diamond sculpturing method based on a triaxial fast tool servo (FTS). In this method, the diamond tool is directly driven by the FTS rather than the ultra-precision lathe to fabricate the micro-structure surfaces. The corresponding toolpath generation algorithm is established to take full advantage of the triaxial FTS. The toolpath is first generated through traditional calculating the shortest tool edge projection on the desired surface and the curve interpolation. The overshoot around the path corner is predicted by simulating the tracking path. Then an extended path is added to the original toolpath to stabilize the overshoot before removing the material. The simulation indicates that the hexagonal lens array can be favorably fabricated by the proposed ultra-precision diamond sculpturing method, and the developed toolpath reduces the form error from 20 to 5nm. The sculpturing experiments of sinusoidal micro-structure array and micro-lens array surfaces suggest that their actual peak-to-valley (PV) form errors are 70nm and 50nm, respectively. The single lens with the surface roughness Sa 3.44nm can be precisely fabricated in 0.1s, demonstrating the high machining efficiency and high machining quality of the proposed ultra-precision diamond sculpturing method.

Physics-informed neural network assisted spherical microphone array signal processing

Thanks to their rotational symmetry that facilitates three-dimensional signal processing, spherical microphone arrays are the common array apertures used for spatial audio and acoustic applications. However, practical implementations of spherical microphone arrays suffer from two issues. First, at high frequency range, a large number of sensors are needed to accurately capture a sound field. Second, the accompanying signal processing algorithm, i.e., the spherical harmonic decomposition method, requires a variable radius array or a rigid surface array to circumvent the spherical Bessel function nulls. Such arrays are hard to design and introduce a scattering field. To address these issues, this paper proposes to assist a spherical microphone array with a physics-informed neural network (PINN) for three-dimensional signal processing. The PINN models the sound field around the array based on the sensor measurements and the acoustic wave equation, augmenting the sound field information captured by the array through prediction. This makes it possible to analyze a high frequency sound field with a reduced number of sensors and avoid the spherical Bessel function nulls with a simple single radius open-sphere microphone array.

AugerPrime surface detector electronics

Operating since 2004, the Pierre Auger Observatory has led to major advances in our understanding of the ultra-high-energy cosmic rays. The latest findings have revealed new insights that led to the upgrade of the Observatory, with the primary goal of obtaining information on the primary mass of the most energetic cosmic rays on a shower-by-shower basis. In the framework of the upgrade, called AugerPrime, the 1660 water-Cherenkov detectors of the surface array are equipped with plastic scintillators and radio antennas, allowing us to enhance the composition sensitivity. To accommodate new detectors and to increase experimental capabilities, the electronics is also upgraded. This includes better timing with up-to-date GPS receivers, higher sampling frequency, increased dynamic range, and more powerful local processing of the data. In this paper, the design characteristics of the new electronics and the enhanced dynamic range will be described. The manufacturing and test processes will be outlined and the test results will be discussed. The calibration of the SD detector and various performance parameters obtained from the analysis of the first commissioning data will also be presented.

Cosmic ray measurements with IceCube and IceTop

IceCube is a cubic-kilometer Cherenkov detector in the deep ice at the geographic South Pole. The dominant event yield in the deep ice detector consists of penetrating atmospheric muons with energies above approximately 300 GeV, produced in cosmic ray air showers. In addition, the surface array, IceTop, measures the electromagnetic component and GeV muons of air showers. Hence, IceCube and IceTop yield unique opportunities to study cosmic rays with unprecedented statistics in great detail. We will present recent results of comic ray measurements from IceCube and IceTop. In this overview, we will highlight measurements of the energy spectrum of cosmic rays from 250 TeV up to the EeV range and their mass composition above 3 PeV. We will also report recent results from measurements of the muon content in air showers and discuss their consistency with predictions from current hadronic interaction models.

Nitrogen-rich carbon nitride (C3N5) coupled with oxygen vacancy TiO2 arrays for efficient photocatalytic H2O2 production

Developing efficient and facilitated recycling photocatalysts for H2O2 formation is an ideal strategy for solar-to-chemical energy conversion. In this work, we synthesized ultrathin C3N5 nanosheets through the process of thermal polymerization and polyvinylpyrrolidone (PVP)-assisted solvent exfoliation. Subsequently, the obtained ultrathin C3N5 nanosheets were tightly attached to the surface of TiO2-x arrays, resulting in an enhanced photocatalytic H2O2 production rate. The density functional theory (DFT) calculations demonstrate that an internal electric field (IEF) is generated between the TiO2-x array and the ultrathin C3N5 due to the different work functions. The presence of IEF provides an additional driving force for carrier separation and transfer in the heterointerface. Benefitting from this unique strategy, the optimal heterojunction obtains the highest H2O2 formation rate (2.93 μmol/L/min), which is about 4.1 times than that of TiO2-x arrays. The rotating disk electrode (RDE) analysis manifests H2O2 formation through 2e--dominated oxygen reduction reaction (ORR). This research provides an innovative strategy for assembling a type-II heterojunction with a useful IEF for efficient photocatalytic H2O2 production.

Recent results of cosmic-ray studies with IceTop at the IceCube Neutrino Observatory

The IceCube Neutrino Observatory is a cubic-kilometer Cherenkov detector that is deployed deep in the Antarctic ice at the South Pole. A square kilometer companion surface detector, IceTop, located directly above in the in-ice array, measures cosmic-ray initiated extensive air showers with primary energies between 100 TeV and 1 EeV. By combining the events measured by IceTop and the in-ice detectors of IceCube in coincidence, we can reconstruct the energy spectra for different primary mass groups. Therefore, we provide information about the origin of cosmic rays, in particular, in the transition region from galactic to extra-galactic origin of high-energy cosmic rays. In this contribution we present recent experimental results, as well as prospects by the foreseen enhancement of the surface detectors of IceTop and the future IceCube-Gen2 surface array.

Droplet boiling on micro-pillar array surface – Nucleate boiling regime

Despite spray cooling in the form of droplet boiling on a textured surface being a very promising phase-change heat dissipating method, the understanding of droplet/bubble two-phase dynamics in the nucleate boiling is extraordinarily limited. In this study, we report sessile droplet boiling on micro-pillar array surface in the nucleate boiling regime using a three-dimensional lattice Boltzmann model comprehensively. Effects of micro-pillar size on bubble behaviors inside droplet are discussed in detail, covering bubble nucleation, growth, coalescence, and rupture. For the micro-pillars with large side length or small spacing, nucleation sites are activated around micro-pillar top surface. The preferential activation location of nucleation sites is determined by temperature, confined space and fluid flow. In bubble growth stage, the variation of bubble radius with time follows the square root law, being consistent with previous experiments. Bubbles merge into a large central bubble beneath droplet for the short micro-pillars while into a vapor layer for the long micro-pillars. Emergence of large central bubble prolongs droplet lifetime but deteriorates heat transfer. In addition, increasing micro-pillar side length or decreasing micro-pillar height can delay activation of nucleation sites.

Analysis and compensation for the dominant tool error in ultra-precision diamond ball-end milling

Diamond ball-end milling is an enabling technology to fabricate complex curved surfaces with a nanometer level roughness. However, limited by the errors of tool manufacturing and installation, the cutting edge profile of a single-bladed diamond milling tool cannot form an ideal sphere crown in rotation, which will significantly worsen the machining accuracy. Although a titled milling method and a tool error reduction method based on milling-test have been proposed to improve the machining accuracy, a complete analysis of the effects of multiple tool errors on the machining accuracy have not been performed. Therefore, the present work contributes an analytical model to accurately calculate the tool rotation profile under various position and orientation errors. The results reveal that the horizontal off-center error of tool cutting edge is the dominant error among all the tool errors. According to the results, a novel high precision identification process is developed to evaluate the horizontal off-center error in view of the cutting-mark, and subsequently a tool center shift method is proposed to compensate for such error. Finally, experiments on millimeter scale spherical surface, micro sphere array and micro sinusoidal surface confirm that the proposed tool error compensation method can significantly improve the form accuracy. The average form errors (PV) of three test surfaces are reduced from 2.29 μm, 0.90 μm and 0.88 μm to 0.61 μm, 0.28 μm and 0.18 μm, respectively.

Green non-fluorinated gradient anisotropic microcolumn array: Enables droplet transition to a low viscosity state on highly viscous substrates

Superhydrophobic surfaces with low adhesion and self-cleaning properties have broad application prospected in various fields. However, the current methods for preparing low-adhesion superhydrophobic surfaces typically require toxic chemicals or fluorination modifications, which are prone to environmental pollution and health hazards, and still face challenges for applications in industries such as food and medical care. This paper aims to prepare anisotropic gradient array surfaces (AGAS) with low adhesion on stainless steel substrates by WEDM, without the need for modification with low-surface-energy materials. AGAS can achieve a stable Cassie state with a low adhesion performance by controlling the dimensional parameters and structural inclination of columnar arrays. Experiments and numerical simulations show that owing to the anisotropic gradient structure, pinning and de-pinning occur asymmetrically in time at the contact lines of the leading and trailing edges of droplets impacting the AGAS. On AGAS, droplets can jump and roll in the direction of gradient descent during the impact process to complete self-cleaning. Due to the discontinuity of the solid–liquid–gas three-phase contact line and the stepped arrangement of the column array, the prepared surface can achieve low adhesion and self-cleaning properties for many common liquid foods in daily life, including milk and juice.