Ultra-low Surface Research Articles

Multiscale Analysis of Hydrodynamic Step Bearing with Ultra Low Surface Separations

The paper presents the multiscale analysis for the hydrodynamic step bearing with ultra low surface clearances where only the physical adsorbed layer is present in the outlet zone and the continuum fluid flow mainly occurs in the inlet zone. This bearing can occur under heavy loads. The flow in the outlet zone is described by the nanoscale flow equation, while the flow in the inlet zone is described by the multiscale flow equation incorporating both the adsorbed layer flow and the intermediate continuum fluid flow. The pressure and carried load of the bearing were derived. Exemplary calculations show that the fluid-bearing surface interaction has the strongest influence on the pressure and carried load of this bearing when the bearing surface clearance is as small as possible, the bearing step size is close to the surface clearance in the outlet zone and the value of the geometrical parameter is the optimum one, which depends on the fluid-bearing surface interaction. For the strong fluid-bearing surface interaction, the carried load of the bearing can be 10 times higher than that calculated from the classical hydrodynamic lubrication theory.

One-step plasma electrolytic oxidation with Graphene oxide for Ultra-low porosity Corrosion-resistant TiO2 coatings

The pores formed by molten material ejection from the discharge channel and rapidly solidification during plasma electrolytic oxidation (PEO) act as passageways for corrosive particles. The overall porosity and pore shape, the inevitable features of ceramic coatings, are main factors that determines the corrosion resistance. In this work, we propose a novel approach that utilizes the advantages of graphene oxide (GO) to alter the pore shape and plasma discharge to effectively reduce the overall porosity. Simultaneously, the overall porosity and pore shape were deconstructed by X-ray microscopy. We found that the GO additive not only formed covalent bonds with the metal oxide, limiting the amount and distribution of molten oxide, but also changed the discharge form of the plasma reaction. The obtained coating exhibited an ultra-low surface porosity (1.10%), ultra-low overall porosity (2.11 vol%), and high aspect ratio (0.7–0.8), which are lowered for 94.8%, 90.9%, and increased for 66.9% than that of the traditional coating, respectively. The ultra-low porosity eliminates channels inside the coating and reduces the number of corrosive ions invading the substrate, resulting in superior corrosion resistance.

Novel approach to improve shale stability using super-amphiphobic nanoscale materials in water-based drilling fluids and its field application

Abstract In this study, super-amphiphobic nano-silica nanoparticles (SA-NPs) were used to enhance the shale stabilization performance of water-based drilling fluids (WBDFs) by altering the surface wettability, preventing the capillary self-priming effect, and plugging the nano-micro pores of shale. The results of transmission electron microscopy, particle size distribution, and scanning electron microscopy characterization revealed that SA-NPs exhibited a nanoscale “coalesce” structure, which is composed of spherical particles joined together, and could form a nano-papillary structure on the shale surface. Due to the presence of nano-micro scale rough structures and ultra-low surface energy components, the shale treated by SA-NPS exhibited super-amphiphobic surface property in the contact angle test. Contact angles of water and hexadecane on the shale surface reached up to 154.13° and 151.34° after being treated with SA-NPs, respectively. Furthermore, the addition of 1% SA-NPs in WBDFs could reduce the linear swelling rate from 40.5 to 6.0%, increase the shale cuttings recovery percentages from 82.5 to 95.6%, increase the plugging rate of low permeability shale core from 81.25 to 94.00%, and raise the high-temperature and high-pressure uniaxial compressive strength from 3.45 to 4.87 MPa. Compared with the polyether amine and fumed nano-silica, the addition of SA-NPs produced the best performance. Based on the excellent shale stabilization performance of SA-NPs, a high-performance WBDF was developed and applied in Dagang Oilfield. During the drilling operation， no wellbore instability, sticking, and other complex situations occurred. The results indicate that SA-NPs could better address the issue of wellbore instability in shale formations and have a great application prospect in shale well drilling.

Impact of the photoelectric threshold sensitivity on the work function determination—Revealing ultra-low work functions of caesiated surfaces

The exploitation of the photoelectric effect is a prominent method for the in situ measurement of the absolute work function of a surface. In the case of metallic surfaces, the Fowler theory is routinely applied for fitting or extrapolating the measured photoelectric yield data to determine the work function value. However, for the reliable application of the Fowler method, attention must be paid to the experimental sensitivity to the photoelectric behavior close to the threshold, which is mainly determined by the signal-to-noise ratio for photocurrent detection and the available photon energies used for irradiation. This is illustrated by means of applying a photoelectric work function measurement system during a Cs coating process of a metal surface, where insufficiently low photon energies or an unfavorable noise level can lead to a severe overestimation of the work function of the order of 1 eV. By a sufficient enhancement of the photoelectric sensitivity, it is now unveiled that ultra-low surface work functions of 1.25 ± 0.10 eV can be generated via caesiation of metallic surfaces (here molybdenum and stainless steel) under vacuum conditions of 10−6–10−5 mbar, which is most probably the result of the formation of an oxidized Cs adlayer.

Ultra-low friction self-levitating nanomagnetic fluid bearing for highly efficient wind energy harvesting

Wind energy provides one of the most sustainable and cleanest forms of energy conversion to tackle the biggest global concern of CO2 emissions from the use of fossil fuels. It is also challenging to build an efficient energy harvester to minimize the losses at several levels during the electrical energy conversion. Herein, we have proposed a novel wind energy harvester that capitalizes on the self-levitation nanomagnetic fluid bearing. The magnetic fluid contains magnetic nanoparticles which sticks to the magnets forming bearing around the edges and providing magnets a passive levitation, which eventually results in an ultra-low frictional surface between the permanent magnet and bottom support surface. The motion of the magnets attached to the rotating fan-shaft assembly driven by the blades and input blowing wind relative to the fixed coils induces a current in the coil. The mechanism has been effectively utilized to develop a highly efficient prototype wind energy harvester, which runs at a very low wind speed of 2 m/s. The prototype wind energy harvester promises to generate 2.59Watt power with an efficiency of 26% at a gentle wind speed (4.5 m/s). Simulations are conducted to support the experimental results of the prototype and the simulation model is further extended to upscale the harvested power for more realistic applications. Our invention has a tremendous potential to produce highly efficient wind energy conversion at a large scale by solving the major problem in the current wind energy conversion systems.

Ultralow loading of Cu2O/CuO nanoparticles on metal-organic framework-derived carbon octahedra and activated semi-coke for highly efficient SO2 removal

A highly efficient desulfurizer is derived from a sacrificial Cu-based metal-organic framework (MOF) template, which is loaded on low-cost activated semi-cokes. The carbonized composite possesses highly-dispersed copper oxide nanoparticles (Cu2O/CuO) as active sites, which are distributed on MOF-derived carbon octahedra and activated semi-cokes. With an ultralow surface loading of 0.19 at% Cu and a high proportion of Cu+, the optimized sample shows an excellent breakthrough time of 822 min and SO2 adsorption capacity of 233.11 mg/g with a steady SO2 removal efficiency of 100%, which is superior to previously reported coke-base desulfurizers in literature. Meanwhile, the best-performed sample shows stability and reversibility for SO2 removal during 10 desulfurization−regeneration cycles. The excellent SO2 removal performance can be attributed to a well-developed porous structure and highly-dispersed copper oxide active sites due to the utilization of both sacrificial MOF template and activated semi-coke.

The Galaxy Replacement Technique (GRT): A New Approach to Study Tidal Stripping and Formation of Intracluster Light in a Cosmological Context

Abstract We introduce the Galaxy Replacement Technique (GRT) that allows us to model tidal stripping of galaxies with very high mass (m star = 5.4 × 104 M ⊙ h −1) and high spatial resolution (10 pc h −1), in a fully cosmological context, using an efficient and fast technique. The technique works by replacing multiple low-resolution dark-matter (DM) halos in the base cosmological simulation with high-resolution models, including a DM halo and stellar disk. We apply the method to follow the hierarchical buildup of a cluster since redshift ∼8 to now, through the hierarchical accretion of galaxies, individually or in substructures such as galaxy groups. We find we can successfully reproduce the observed total stellar masses of observed clusters since redshift ∼1. The high resolution allows us to accurately resolve the tidal stripping process and well describe the formation of ultralow surface brightness features in the cluster (μ V < 32 mag arcsec−2) such as the intracluster light (ICL), shells, and tidal streams. We measure the evolution of the fraction of light in the ICL and brightest cluster galaxy using several different methods. While their broad response to the cluster-mass growth history is similar, the methods show systematic differences, meaning we must be careful when comparing studies that use distinct methods. The GRT represents a powerful new tool for studying tidal effects on galaxies and exploring the formation channels of the ICL in a fully cosmological context and with large samples of simulated groups and clusters.

Exploiting Molecular Dynamics in Composite Coatings to Design Robust Super-Repellent Surfaces.

Fluorinated motifs are promising for the engineering of repellent coatings, however, a fundamental understanding of how to effectively bind these motifs to various substrates is required to improve their stability in different use scenarios. Herein, the binding of fluorinated polyhedral oligomeric silsesquioxanes (POSS) using a cyanoacrylate glue (binder) is computationally and experimentally evaluated. The composite POSS–binder coatings display ultralow surface energy (≈10 mJ m−2), while still having large surface adhesions to substrates (300–400 nN), highlighting that super‐repellent coatings (contact angles >150°) can be readily generated with this composite approach. Importantly, the coatings show super‐repellency to both corrosive liquids (e.g., 98 wt% H2SO4) and ultralow surface tension liquids (e.g., alcohols), with ultralow roll‐off angles (<5°), and tunable resistance to liquid penetration. Additionally, these coatings demonstrate the potential in effective cargo loading and robust self‐cleaning properties, where experimental datasets are correlated with both relevant theoretical predictions and systematic all‐atom molecular dynamics simulations of the repellent coatings. This work not only holds promise for chemical shielding, heat transfer, and liquid manipulations but offers a facile yet robust pathway for engineering advanced coatings by effectively combining components for their mutually desired properties.

Intravital microscopic observation of the microvasculature during hemodialysis in healthy rats

Hemodialysis (HD) provides life-saving treatment for kidney failure. Patient mortality is extremely high, with cardiovascular disease (CVD) being the leading cause of death. This results from both a high underlying burden of cardiovascular disease, as well as additional physiological stress from the HD procedure itself. Clinical observations indicate that HD is associated with microvascular dysfunction (MD), underlining the need for a fundamental pathophysiological assessment of the microcirculatory consequences of HD. We therefore successfully developed an experimental small animal model, that allows for a simultaneous real-time assessment of the microvasculature. Using in-house built ultra-low surface area dialyzers and miniaturized extracorporeal circuit, we successfully dialyzed male Wistar Kyoto rats and combined this with a simultaneous intravital microscopic observation of the EDL microvasculature. Our results show that even in healthy animals, a euvolemic HD procedure can induce a significant systemic hemodynamic disturbance and induce disruption of microvascular perfusion (as evidence by a reduction in the proportion of the observed microcirculation receiving blood flow). This study, using a new small animal hemodialysis model, has allowed direct demonstration that microvascular blood flow in tissue in skeletal muscle is acutely reduced during HD, potentially in concert with other microvascular beds. It shows that preclinical small animal models can be used to further investigate HD-induced ischemic organ injury and allow rapid throughput of putative interventions directed at reducing HD-induced multi-organ ischemic injury.

KCa1.1 K+ Channel Inhibition Overcomes Resistance to Antiandrogens and Doxorubicin in a Human Prostate Cancer LNCaP Spheroid Model.

Several types of K+ channels play crucial roles in tumorigenicity, stemness, invasiveness, and drug resistance in cancer. Spheroid formation of human prostate cancer (PC) LNCaP cells with ultra-low attachment surface cultureware induced the up-regulation of cancer stem cell markers, such as NANOG, and decreased the protein degradation of the Ca2+-activated K+ channel KCa1.1 by down-regulating the E3 ubiquitin ligase, FBXW7, compared with LNCaP monolayers. Accordingly, KCa1.1 activator-induced hyperpolarizing responses were larger in isolated cells from LNCaP spheroids. The pharmacological inhibition of KCa1.1 overcame the resistance of LNCaP spheroids to antiandrogens and doxorubicin (DOX). The protein expression of androgen receptors (AR) was significantly decreased by LNCaP spheroid formation and reversed by KCa1.1 inhibition. The pharmacological and genetic inhibition of MDM2, which may be related to AR protein degradation in PC stem cells, revealed that MDM2 was responsible for the acquisition of antiandrogen resistance in LNCaP spheroids, which was overcome by KCa1.1 inhibition. Furthermore, a member of the multidrug resistance-associated protein subfamily of ABC transporters, MRP5 was responsible for the acquisition of DOX resistance in LNCaP spheroids, which was also overcome by KCa1.1 inhibition. Collectively, the present results suggest the potential of KCa1.1 in LNCaP spheroids, which mimic PC stem cells, as a therapeutic target for overcoming antiandrogen- and DOX-resistance in PC cells.

Periodic in-filled pipes embedded in semi-infinite space as seismic metamaterials for filtering ultra-low-frequency surface waves

The use of artificial periodic structures such as periodic wave barriers and seismic metamaterials has attracted attention as an effective approach to reduce the impact of ambient vibrations or earthquakes. In previous research, a large amount of steel was usually used in the design of seismic metamaterials to achieve ultra-low surface wave band gaps (BGs). However, the use of such large amounts of steel is inconvenient and expensive in practical engineering applications. To address this issue, this study considered the use of common building materials, namely, concrete, rubber, and soil, for the preparation of seismic metamaterials. Using these three materials, a one-dimensional (1D) seismic metamaterial composed of periodic in-filled pipes and a substrate was proposed. Ultra-low surface wave BGs (0–10 Hz) of the seismic metamaterial were identified using the sound cone method. Several important geometrical and material parameters that could influence the BGs were studied. Based on the 1D metamaterial, a 2D seismic metamaterial with a complete ultra-low BG was proposed to filter Rayleigh waves at any angle in the surface plane. The screening effectiveness of the 1D and 2D seismic metamaterials was evaluated using 2D and 3D numerical models, respectively. The results show that the ultra-low BG width decreases with an increase in the distance between two adjacent in-filled pipes. The small height of the in-filled pipe is beneficial for achieving a large ultra-low BG. A high elastic modulus and a low mass density of the soft filling material correspond to a large ultra-low BG width. The generation of ultra-low BGs in both 1D and 2D seismic metamaterials is attributed to the torsional resonance of the filling soft material. This study can serve as a reference for the design of new seismic metamaterials with practical value in engineering.

Water-repellent hierarchical microstructured PTFE films via micro powder hot embossing

The preparation of hierarchical microstructured surfaces to obtain different wettability has been studied in both academy and industry. Polytetrafluoroethylene (PTFE) is an ideal material for preparing superhydrophobic surface due to its ultra-low surface energy. However, it is still a challenge to prepare hierarchical structure on the surface of PTFE. In this paper, PTFE films with hierarchical structure were successfully prepared by micro powder hot embossing (mPHE) process. Through characterization, the maximum contact angle and minimum sliding angle can reach up to 164° and 5.3° respectively. The influence of processing parameters and particle size on forming qualities was discussed. A dimensionless indicator was proposed to successfully describe the hierarchical character and characterize the relationship between wetting states and forming quality. Finally, a series of mechanical and chemical durability tests were carried out, verifying the practical application value of the prepared PTFE films.

An Ultra-Low Power Surface EMG Sensor for Wearable Biometric and Medical Applications.

In recent years, the surface electromyography (EMG) signal has received a lot of attention. EMG signals are used to analyze muscle activity or to evaluate a patient’s muscle status. However, commercial surface EMG systems are expensive and have high power consumption. Therefore, the purpose of this paper is to implement a surface EMG acquisition system that supports high sampling and ultra-low power consumption measurement. This work analyzes and optimizes each part of the EMG acquisition circuit and combines an MCU with BLE. Regarding the MCU power saving method, the system uses two different frequency MCU clock sources and we proposed a ping-pong buffer as the memory architecture to achieve the best power saving effect. The measured surface EMG signal samples can be forwarded immediately to the host for further processing and additional application. The results show that the average current of the proposed architecture can be reduced by 92.72% compared with commercial devices, and the battery life is 9.057 times longer. In addition, the correlation coefficients were up to 99.5%, which represents a high relative agreement between the commercial and the proposed system.

Frost layer growth behavior on ultra-low temperature surface with a superhydrophobic coating

Experimental research was conducted to study the frost formation on superhydrophobic surfaces at ultra-low temperatures, which might broaden the insight into frost growth behavior on the heat exchangers. The frost properties were examined over time, and the frost retardation according to the frosting factor was identified using the frost reduction ratios. The ablimation-dominant (desublimation) mechanism was observed at ultra-low temperatures in which almost no water droplets were generated. Consequently, the influence of the superhydrophobic surface on frost retardation was insignificant within −5% owing to the frosting mechanism. It is difficult to expect an increase in thermal performance of heat exchangers by applying superhydrophobic surfaces; using superhydrophobic surfaces for the purpose of frost retardation at ultra-low temperatures is not recommended.

Development of a novel wind to electrical energy converter of passive ferrofluid levitation through its parameter modelling and optimization

The exclusive properties of passive levitation and ultra-low friction surface formation of ferrofluids have been utilized to design a highly efficient wind energy harvester. A novel design of passive ferrofluid levitation wind energy converter has been proposed and laboratory prototype has been developed. The simulation model has been developed using the ANSYS Workbench Maxwell electromagnetic software and validated by the experimental results. In this paper, different approaches such as response surface method (RSM), central composite design (CCD) and artificial neural network (ANN) modelling have been applied to relate the system output power to the input design parameters of the wind energy harvester system. The sensitivity analysis of design parameters and their interactions have been conducted. The CCD and RSM modelling have been applied for predicting the power output from the design parameters for the energy harvester where the design parameters has been optimized for the maximum power output using the genetic algorithm (GA). Also, the RSM modelling is validated by the analysis of variance. As a result, the optimal design parameter combination to produce the highest power output can be identified. The optimization result will be compared with and verified by the prediction result of the ANN model. It is found that within the range of the design parameters, the maximum power output of the wind energy harvester obtained through the RSM with the GA is close to that predicted by the ANN model. The design optimization method can be extended to develop an upscale model of the wind energy harvester for larger power output. The proposed magnetic levitation technology has many more potential applications in sensors and actuators, cooling and mechanical bearings and in health sectors.

Self-Induced Type-I Band Alignment at Surface Grain Boundaries for Highly Efficient and Stable Perovskite Solar Cells.

The open-circuit voltage (VOC ) of perovskite solar cells (PSCs) is reported to be significantly weakened by carrier loss at the film surface. Here, the moisture condensation at only the upper surface of perovskite films is controlled by constructing an ultralow surface temperature. Then, type-I band alignment can be formed at the surface grain boundaries due to the etching effect of trace amounts of condensed moisture. The beneficially constructed surface type-I band alignment can effectively repel carriers and return them to the inside of the grain, significantly avoiding the carrier loss at films surface. As a result, a superior carrier lifetime exceeding 2.5µs is obtained and the VOC of PSC is remarkably boosted from 1.07 to 1.17V. The minimum VOC deficit of only 0.39V enables a substantial gain in power conversion efficiency (PCE) from 20.2% to 22.4% in one-step spin-coating methods. Moreover, this innovation is versatile and a champion PCE of 23.2% is also achieved in two-step spin-coating methods.

Persistent Water Repellency of Syndiotactic Polymethylene with Perfluoroethyl Hexyloxycarbonyl Side Chains.

Polyacrylates bearing long fluoroalkyl (Rf) side chains are known to have ultralow surface energies that are appropriate for functional coating and fabric finishing. However, these long Rf chains cause health concerns because of the risk of toxic and bioaccumulative perfluoroalcanoic acid emission via oxidative degradation. This work demonstrates that incorporating a short Rf chain of perfluoroethylene at the end of the side chains of syndiotactic poly(substituted methylene) (PM) produces hydrophobicity. A contact angle of 105° of PM remains constant for more than 50 s, whereas that of the polyacrylate (PA) with the same side chain rapidly decreases from 85° to 44° over the same period. Such persistent water repellency of the PM is ascribed to a liquid crystal structure comprised the main chains arranged in a 2D hexagonal lattice and side chains that extend perpendicularly from these main chains.

Fluorinated Carbon Nanotube Superamphiphobic Coating for High-Efficiency and Long-Lasting Underwater Antibiofouling Surfaces.

Biofilm formation on the surface of materials has brought great troubles to various industries. Designing surfaces with long-lasting antibiofouling properties can help restrain primary bacterial and protein attachment and subsequent biofilm formation for a long time, which is also of great significance for industrial applications. In this work, we successfully prepared fluorinated carbon nanotubes through a one-step fluorination method using fluorosilane and fabricated a superamphiphobic coating using a simple spray method. This coating with ultralow surface free energy and stable micro/nano structures achieved highly efficient and long-term underwater antibiofouling properties. Tea, milk, BSA, and bacterial solution can bounce highly on this surface without wetting the surface in air. The long-term existence of the underwater air-bubble layer on the surface of the superamphiphobic coating was observed. Thus, this surface can effectively resist BSA and bacterial attachment (E. coli), and the efficiency, respectively, reaches 97.5 and 98.2%. Even if it is fully soaked in BSA and BS solution for 120 h, the whole surface is still able to repel water, BSA, and BS solution very well. In addition, the coating possessed excellent wear resistance, the CAs of BSA and BS solution just decreased slightly (higher than 158°), and the sliding angles increased slightly (lower than 4°) after 50 tape abrasion cycles. Therefore, this superamphiphobic coating may have promising applications for marine devices, biomedical materials, protective clothing, and chemical shielding.

Break type and interactions from ultra-deep optical imaging of isolated galaxies

AbstractIn the standard cosmological model of galaxy evolution, mergers and interactions play a fundamental role in shaping galaxies. Galaxies that are currently isolated are thus interesting, allowing us to identify how internal or external processes impact galactic structure. However, current observational limits may be obscuring crucial information in the low-mass or low-brightness regime. We use the AMIGA catalog of isolated galaxies to explore the impact of different factors on the structure of these galaxies. In particular, we study the type of disk break based on the degree of isolation and the presence of interactions which are only detectable in the ultra-low surface brightness regime. We present the first results of an extensive observational campaign of ultra-deep optical imaging targeting a sample of 25 low-redshift (z &lt; 0.035) isolated galaxies. The nominal surface brightness limits achieved are comparable to those to be obtained in the 10-year LSST coadds ( mag arcsec−2; 3σ ; 10” × 10”). We find that isolated galaxies have a considerably higher fraction of purely exponential disk profiles and a lower presence of up-bending breaks than field or cluster galaxies. Our extreme imaging depth allows us to detect the presence of previously unreported interactions with minor companions in some of the galaxies in our sample (∼40% of the galaxies show signs of interaction). The results of our work fit with the general framework of galactic structure in which up-bending breaks (Type III) would be produced by mergers and down-bending breaks (Type II) due to a threshold in star formation that would tend to become single exponential disk (Type I) in case of cessation or decrease of star formation.

Study of Thermal Conductivity in Two-dimensional Bi2Te3 from Micro- Raman Spectroscopy

Background: Topological insulator (TI), Bi2Te3 is a new class of quantum materials. Having ultralow dissipation surface states, TIs hold great promise toward different potential applications. Micro-Raman spectroscopy is a conventional and non-destructive technique, which has been widely used to characterize the structural and electronic properties of thermoelectric materials. Objective: The objective of this study is to review power dependent and temperature dependent Raman spectra of B2Te3 nanoflakes on SiO2/Si substrate to estimate the temperature coefficient and thermal conductivity of these flakes for possible application of this material in thermoelectrics. Methods: Bi2Te3 flakes of different thicknesses were mechanically exfoliated from high-quality bulk Bi2Te3 crystal using scotch tape on 300 nm SiO2/ Si substrates. The power dependent and temperature dependent Raman spectra were acquired with the help of HORIBA LabRAM confocal micro- Raman system in a backscattering geometry. Result: The observed power dependent and temperature dependent Raman spectra of Bi2Te3 nanoflakes follow the same trend as discussed in various pieces of literature. From temperature coefficient and power coefficient values, the in-plane thermal conductivity has been estimated, which is found to be in the order of 102 W/m-K. The enhancement in the thermal conductivity suggests that the underlying substrate significantly affects the heat dissipation of the Bi2Te3 flake based on the coupling strength with Bi2Te3. Conclusion: This work provides a good platform to understand the role of the substrate on the thermal conductivity of exfoliated Bi2Te3 nanoflakes and this study can be extended to other substrates.