Macroscopic Surface Research Articles

Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review

Heavy metal ions (HMIs) pose a serious threat to the environment and human body because they are toxic and non-biodegradable and widely exist in environmental ecosystems. It is necessary to develop a rapid, sensitive and convenient method for HMIs detection to provide a strong guarantee for ecology and human health. Ion-imprinted electrochemical sensors (IIECSs) based on nanomaterials have been regarded as an excellent technology because of the good selectivity, the advantages of fast detection speed, low cost, and portability. Electrode surfaces modified with nanomaterials can obtain excellent nano-effects, such as size effect, macroscopic quantum tunneling effect and surface effect, which greatly improve its surface area and conductivity, so as to improve the detection sensitivity and reduce the detection limit of the sensor. Hence, the present review focused on the fundamentals and the synthetic strategies of ion-imprinted polymers (IIPs) and IIECSs for HMIs detection, as well as the applications of various nanomaterials as modifiers and sensitizers in the construction of HMIIECSs and the influence on the sensing performance of the fabricated sensors. Finally, the potential challenges and outlook on the future development of the HMIIECSs technology were also highlighted. By means of the points presented in this review, we hope to provide some help in further developing the preparation methods of high-performance HMIIECSs and expanding their potential applications.

Bubble Formation in Magma

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions. ▪ We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate. ▪ Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism. ▪ Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation. ▪ Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways.

Research Progress of Polymers/Inorganic Nanocomposite Electrical Insulating Materials.

With the rapid development of power, energy, electronic information, rail transit, and aerospace industries, nanocomposite electrical insulating materials have been begun to be widely used as new materials. Polymer/inorganic nanocomposite dielectric materials possess excellent physical and mechanical properties. In addition, numerous unique properties, such as electricity, thermal, sound, light, and magnetic properties are exhibited by these materials. First, the macroscopic quantum tunneling effect, small-size effect, surface effect, and quantum-size effect of nanoparticles are introduced. There are a few anomalous changes in the physical and chemical properties of the matrix, which are caused by these effects. Second, the interaction mechanism between the nanoparticles and polymer matrix is introduced. These include infiltration adsorption theory, chemical bonding, diffusion theory, electrostatic theory, mechanical connection theory, deformation layer theory, and physical adsorption theory. The mechanism of action of the interface on the dielectric properties of the composites is summarized. These are the interface trap effect, interface barrier effect, and homogenization field strength effect. In addition, different interfacial structure models were used to analyze the specific properties of nanocomposite dielectric materials. Finally, the research status of the dielectric properties of nanocomposite dielectric materials in the electrical insulation field is introduced.

Triaxial test and microstructure analysis of soil from alkali contaminated sites

The protection of site cultural relics is facing great challenges of site soil instability and contamination. Targeting at the special geological environment of Kaifeng region, the affecting laws of different concentrations of alkali on mechanical properties of site soil in this region are studied in this paper. The triaxial test is conducted to study the mechanical properties of site soil, including its failure pattern, stress-strain relationship, stress path and strength index, etc. The X-ray diffraction test and scanning electron microscope test are used to analyze the composition, particle state, and pore characteristics of the soil before and after contamination, and to evaluate the stability of the site soil. At the site combining with microstructure changes and macro mechanical properties. The results show that, from the macroscopic surface, with the increase of alkali concentration, the failure shear plane usually appears along the 45° direction. From the perspective of mechanical properties, the stress-strain relationship of the site soil is caused by the strengthening of soil deformation, and the alkali concentration increases, and the curve gradually develops from hardening type to softening type. The stress path is the line connecting the points in the sequence of the stress change process, which is different, and the corresponding soil deformation and strength characteristics will also appear very different. The stress path of soil with different alkali concentration is different. Under the same σ3 condition, the stress σ1 is different. The stress change is expressed in macroscopic terms as different forms of soil damage. Under 0 % concentration, the strength index of soil is 82.14 kPa, 21.67°, and the alkali concentration is 4–16 %, the internal friction Angle is gradually increased, and the cohesion is slightly reduced. From the micro perspective, the main components of the contaminated site soil are SiO2, Al2O3, CaO and Fe2O3. In the process of alkali-soil reaction, alkali reacts with oxides in soil to form Na2AlO2, which has a certain cementation effect. SiO2 reacts with NaOH solution to generate Na2SiO3, which has strong cohesiveness and strength. The newly generated cementing material in the soil increases, and the bonding force between particles increases. In addition, some cements fill the inner pores and improve the shear strength of soil. Under the same pressure, the stress-strain curve of soil gradually developed from hardening type to softening type with the increase of alkali concentration. In the stress-strain curve of soil, with the increase of alkali concentration, the soil reaches the strength at failure under small deformation. The increase of alkali concentration reduces the plasticity and increases the brittleness of soil. At this time, if the stress is localized, shear bands will appear and the stability of soil will decrease. The study of soil properties changes caused by different alkali pollution concentrations can provide a scientific basis for the reinforcement and protection of soil sites or ancient cultural foundations in Kaifeng area.

Nanostructured TiNb coating improves the bioactivity of 3D printed PEEK

Polyetheretherketone (PEEK) has mechanical properties suitable for the manufacturing of osseointegration implants. However, its biological properties can be significantly improved by surface modification. In this work, the macroscopic surface topography was obtained by 3D printing and then the 3D printed surface was coated with a TiNb layer. The coating made it possible to apply anodic oxidation, by which a surface with defined nanoscale topography was obtained. Thus, a material with a gradient surface topography and suitable chemical composition was prepared. The properties of the surface were analyzed using optical and scanning electron microscopy. The chemical composition was then evaluated by photoelectron spectroscopy. The roughness, the wettability, and the wear resistance of the surface were observed. The adhesion of the coating and the oxide layer was evaluated. The biological activity of samples was analyzed by seeding them with human osteoblast-like Saos-2 cells. The cell adhesion, proliferation, metabolic activity and viability was observed and was statistically evaluated. After this, the functionality of this surface modification was tested by applying it to an implant with a real geometry. The main conclusions show that the nanostructured TiNb layer on 3D printed PEEK significantly improves biological activity.

Effect of Macroscopic Surface Heterogeneities on an Advancing Contact Line.

The shape of a liquid-air interface advancing on a heterogeneous surface was studied experimentally, together with the force induced by the pinning of the contact line to surface defects. Different surfaces were considered with circular defects introduced as arrays of cocoa butter patches or small circular holes. These heterogeneous surfaces were submerged in aqueous ethanol solutions while measuring the additional force arising from the deformation of the advancing contact line and characterizing the interface shape and its pinning on the defects. Initially, the submersion force is linear with submerged depth, suggesting a constant defect-induced stiffness. This regime ends when the contact line depins from the defects. A simple scaling is proposed to describe the depinning force and the depinning energy. As the defect separation increases, the interface stiffness is found to increase too, with a weak dependency on the defect radius. This interaction between defects cannot be captured by simple scaling but can be well predicted by a theory considering the interface deformation in the presence of a periodic arrays of holes. Creating a four-phase contact line by including solid defects (cocoa butter) reduced pinning forces. The radius of the defect had a nonlinear effect on the depinning depth. The four-phase contact line resulted in depinning before the defects were fully submerged. These experimental results and the associated theory help to understand quantitatively the extent to which surface heterogeneities can slow down wetting. This in turn paves the way to tailoring the design of heterogeneous surfaces toward desired wetting performances.

Linking macroscopic surface morphology of activated carbon fibres and electrosorption performance: An electrochemical impedance spectroscopy and capacitive deionization study

Activated carbon fibres (ACFs) are successful electrode materials for capacitive deionization (CDI) owing to their excellent electrochemical properties and commercial availability, for example, with knitted or woven morphology patterns. However, the lack of a common and effective analytical framework to analyse the performance of ACFs is hindering further progress in the area. This study establishes an electrochemical impedance-based method to detect and investigate the electrochemical properties of ACF materials without destroying their original weaving patterns. Five commercial ACFs with two distinct patterns and similar specific surface areas were investigated. Data from electrochemical impedance spectroscopy (EIS) are compared to the desalination performance and energy consumption of the ACFs in a CDI cell. The weaving pattern played a role in the electrochemical properties and desalination performance. The volume-salt adsorption capacities in CDI were related to the volume-specific capacities in EIS, however, there was no significant difference between knitted and woven materials. Linked to EIS features, knitted ACFs consume less energy than woven ACFs for removing the same amount of NaCl from water. These results provide ACF researchers with a new, effective, and readily available approach for measuring the electrochemical performance of ACF materials via EIS.

Spread and adsorbed layers of protein fibrils at water –air interface

The properties of adsorbed layers of protein fibrils differ significantly from the properties of fibril spread layers on an aqueous subphase. If the dependencies of the dynamic surface elasticity on surface pressure of Lysozyme (LYS) and β-lactoglobulin (BLG) aqueous dispersions proved to be close to the results for native protein solutions, LYS and BLG spread layers on the surface of 0.1 M NaCl solution exhibited the surface elasticity more than two times higher than the values for protein solutions with the same NaCl concentatration, presumably due to lower surface concentrations of hydrolysed peptides in the latter case. The properties of fibril spread and adsorbed layers and also their morphology, unlike the surface properties of protein solutions, depend noticeably on the ionic strength of the aqueous bulk phase. This dependence is stronger in case of LYS layers, which are also more prone to the formation of macroscopic and mesoscopic surface aggregates as compared with BLG layers.

(Invited) Optical Characterization of Bulk GaN Substrates and Homoepitaxial Films

Low ON-resistance and high breakdown voltage, made possible by improved critical electric field and mobility, has promoted GaN from a potential to the most promising semiconductor material for use in the next-generation of medium- and high voltage-power converters. The commercial availability of large area substrates, produced by HVPE (Hydride Vapor Phase Epitaxial, a quasi-bulk deposition technique) and ammonothermal bulk growth method, provides wafers with reduce concentrations of extended defect, allows the deposition of electronic grade epitaxial films and the realization of high performance electronic devices. Despite that, many steps of substrate preparation, such as miss-cut orientation and surface finishing, must be improved and standardized to yield reproducible epitaxial film growth. To verify the importance of substrate characteristics on the intrinsic properties of homoepitaxial MOCVD films, we initially evaluated substrate provided by various commercial supplies. The substrate effects on epi morphology, uniformity, and impurity incorporation were substantiated by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers.All evaluated substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling the detection of different concentrations of grain boundaries, impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conductive regions. The substrates can be grouped in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy.If time permits, results from vertical Schottky diodes, fabricated to quickly evaluate device performance, will presented. While most of the films showed the ability to withstand high electric fields, more uniform electrical properties were observed for those grown on substrates having more uniform properties. These results show that improving bulk substrates is the path to high voltage vertical devices, and that such substrates have a significant influence on device performance. Acknowledgments: Work at NRL is supported by the Office of Naval Research

Microstructure and Properties of ZrB2-SiC Reinforced Copper Matrix Composite Coatings Prepared by Laser Cladding.

With the use of electrolytic Cu powder, Zr powder, Si powder and nickel-coated B4C powder as cladding powders, in-situ synthesized ZrB2-SiC reinforced copper matrix composite coatings were prepared by laser cladding on the surface of the copper substrate to improve the surface hardness and wear resistance. Under the condition of a laser energy density at 60 kJ/cm2, the macroscopic surface of the composite coating was continuously flat. The microstructure and phase of the cladding coating were analyzed by means of XRD and SEM. The reinforcements with nano-scale particle and micron-scale needle-like structures were in-situ synthesized in the cladding coating, and the content of the reinforcement phase decreased slightly from the coating surface to the substrate. The phase analysis results showed that the reinforcements included ZrB2 and SiC. When the content of the reinforcement was increased to 30 wt%, microhardness also increased from 48 HV0.2 to 309 HV0.2, which was about 5.6 times that of the copper matrix. The wear resistance of the composite coatings was characterized by current-carrying wear tests. By keeping the sliding speed and load constant, the wear rate decreased with an increase in the reinforcement content, and the wear mechanism changed from adhesive wear to abrasive wear. The wear rate of the composite coating with the current was higher than that without the current due to its electric ablation and high temperature.

Characterization of the white deposit on the surface of cement mortars by correlative light-electron microscopy (CLEM)

This study focuses on the characterization of white deposit occurring after wet/dry cycles on the surface of cement mortars presenting large amount of AFt phase. Correlative light-electron microscopy (CLEM) was confirmed to be a powerful method in characterizing and identifying microscopic visible white deposit that causes macroscopic visible surface whitening in those cement mortars. It was discovered that the white deposit formed after wet/dry cycles was caused by solids precipitated on the surface of cement mortars during hydration and/or on drying, and those solids were composed of CaCO3, AFt, AFm or their solid solutions. Due to the resolution limit of the human eye, there is a threshold size 100 μm for the microscopic visible white deposit or its cluster to become macroscopic visible surface whitening. Partial covering of red pigments by the newly formed solids on the surface of the cement mortars further confirmed the relationship between the size and quantity of microscopic visible white deposit and macroscopic visible surface whitening.

Spatially resolved roughness exponent in polymer fracture

The fracture surface of slow and continuous crack propagation during environmental stress cracking of a semicrystalline polyethylene exhibits isotropic roughness exponents at the local scale but resolved across the macroscopic fracture surface a clear position dependence is found. The spatially resolved roughness exponent admits values in the range between 0.1 and 0.4, demonstrating nontrivial exponents in the small length-scale regime. Instead, they vary across the fracture surface according to the stress-state distribution, which suggests that the exponents are intimately linked to the locally dominating dissipation processes during craze cracking.

A Study of the Critical Velocity of the Droplet Transition from the Cassie to Wenzel State on the Symmetric Pillared Surface

A droplet hitting a superhydrophobic surface will undergo the Cassie to Wenzel transition when the wetting force exceeds the anti-wetting force. The critical velocity of the droplet’s Cassie to Wenzel state transition can reflect the wettability of the surface. However, the critical velocity research is still at the microscale and has not been extended to the nanoscale mechanism. A cross-scale critical velocity prediction model for superhydrophobic surfaces with symmetric structures is proposed here based on a mechanical equilibrium system. The model’s applicability is verified by experimental data. It demonstrates that the mechanical equilibrium system of droplet impact with capillary pressure and Laplace pressure as anti-wetting forces is more comprehensive, and the model proposed in this study predicts the critical velocity more precisely with a maximum error of 12% compared to the simulation results. Furthermore, the correlation between the simulation at the nanoscale and the evaluation of the macroscopic symmetrical protrusion surface properties is established. Combined with the model and the correlation, the relationship between the microscopic mechanism and the macroscopic examination of droplet dynamics on the superhydrophobic surface be presented, and the wettability evaluation method of macroscopic surfaces based on the molecular simulation mechanism can be realized.

Biointerface Engineering with Nucleic Acid Materials for Biosensing Applications (Adv. Funct. Mater. 37/2022)

Biointerface Engineering In article number 2201069, Mingshu Xiao, Chengqing Yi, Hao Pei, and co-workers focus on nucleic acid-engineered bio-interfaces (including nano-surfaces, cell surfaces, and macroscopic surfaces) and their use in chemical and biological sensing. They review the current development in nucleic acid-engineered bio-interface-based biosensors and how the rational design of such constructs leads to more efficient biosensing platforms.

Cover Picture: Materials and Corrosion. 9/2022

Cover:Macroscopic surface images of Ni‐based alloys with 30 wt.% Cr (modelled after the commercial Alloy 699 XA) after exposure to harsh metal dusting conditions. The sample on the left has an additional 1 wt.% Fe, whereas the sample on the right possesses 4 wt.% Fe and 2 wt.% Al. The study evaluates the beneficial effects of Al together with low amounts of Fe on the resistance against pitting attack.More detailed information can be found in: Gunilla Herting, Clara Schlereth, Ceyhun Oskay, Heike Hattendorf, Benedikt Nowak, Mathias C. Galetz, Influence of Al and Fe Additions on Metal Dusting of NiCr‐Alloys, Materials and Corrosion 2022, 73, 1346.

Comparison of Models to Predict Mechanical Properties of FR-AM Composites and a Fractographical Study

Continuous fiber-reinforced additive manufacturing (cFRAM) composites improve the mechanical properties of polymer components. Given the recent interest in their mechanical performance and failure mechanisms, this work aims to describe the principal failure mechanisms and compare the prediction capabilities for the mechanical properties, stiffness constants, and strength of cFRAM using two distinct predictive models. This work presents experimental tensile tests of continuous carbon fiber AM composites varying their reinforced fraction, printing direction, and fiber angle. In the first predictive model, a micromechanical-based model for stiffness and strength predicts their macroscopic response. In the second part, data-driven models using different machine learning algorithms for regression are trained to predict stiffness and strength based on critical parameters. Both models are assessed regarding their accuracy, ease of implementation, and generalization capabilities. Moreover, microstructural images are used for a qualitative evaluation of the parameters and their influence on the macroscopic response and failure surface topology. Finally, we conclude that although predicting the mechanical properties of cFRAM is a complex task, it can be carried on a Gaussian process regression and a micromechanical model, with good accuracy generalized onto different process parameters specimens.

Investigation of Rock Burst Mechanism under Thermomechanical Coupling Conditions Based on Rock Mechanical Tests

Abstract The thermomechanical (TM) coupling effects of rock bursts have attracted considerable attention from researchers owing to the high geothermal and geostresses in deep tunnels in regions such as Western China. To study the brittleness and rock burst mechanism under TM conditions, various tests, such as splitting, uniaxial compression, rock burst tendency, and rock burst physical model tests, were conducted at temperatures ranging from 20°C to 80°C. The results revealed that, when granite samples were heated, their tensile strengths decreased in the splitting tests. Their peak stresses and the corresponding strains increased; their macroscopic tensile fracture surfaces became more evident; and the microcosmic tensile properties of intergranular fractures became prominent under uniaxial compression. Rock burst physical model tests and acoustic emission monitoring results revealed that, at higher temperatures, the fracture degree and failure range were larger, the energy was higher and more concentrated during failure, and failure occurred earlier. The brittleness index B, rock burst tendency Wet, and σθ/σc all exhibited a clear increasing tendency with an increase in temperature. The rock burst mechanism, considering the temperature effect, can be summarized as follows: the increase in brittle tensile fracture components and geostress caused by temperature increasing is conducive to the rapid release of energy, which will promote the occurrence of rock burst. The researching result is of great academic value and practical significance for the prevention, design, and safe construction of rock burst in deep high geothermal tunnels.

Effect of sodium alginate on the properties of microbial repair materials and its repair effect on mortar crack

In recent years, microbial repair materials have received widespread attention for their advantages such as stable products and good compatibility with cementitious materials. However, the current construction process of microbial repair materials is mainly by immersion, which limits the more widespread application. Therefore, this study proposed a coating construction process with sodium alginate as the carrier. The effects of sodium alginate concentration and dosing on the fundamental properties of microbial repair materials (CaCO3 content, mechanical properties, water absorption ratio, and heating shrinkage rate) and their effects on mortar repair effects (macroscopic morphology and surface water absorption ratio) were investigated. The repair effects were further verified by combining thermogravimetric analysis of repair products and scanning electron microscopy. The results showed that 1) the microbial repair material had better basic properties when sodium alginate solution with a mass concentration of 1.5% was used, and its solution-to-bacterial solution volume ratios were 8:2, 7:3, and 6:4; 2) using the coating technique, the microorganisms were fixed in the cracks on the mortar surface by using sodium alginate as the carrier. Only twice of repair could generate a mixture of calcium alginate and calcium carbonate crystals in the cracks by close adhesion. The surface water absorption of the repaired specimens was 67% lower than before the repair, which is a significant effect of the repair.

Self-organization and tunable characteristic lengths of two-dimensional hexagonal superlattices of nanowires directly grown on substrates

The organization of nano-objects on macroscopic surfaces is a key challenge for the technological improvement and implementation of nanotechnologies. For achieving operational functions, it is required to assemble nano-objects as controllable building blocks in highly ordered superstructures. Herein, we demonstrate the growth and self-organization of metallic nanowires on surfaces into hexagonal superlattices with tunable characteristic lengths depending of the stabilizing surfactants employed. Starting from a reacting mixture containing a Pt(111) substrate, a Co organometallic precursor, an amine, and an acid dissolved in a solvent, we quantify the structural evolution of superlattices of vertical single-crystalline Co nanowires on Pt, using a combined analysis of small angle neutron scattering, transmission, and scanning electron microscopies. We show the concerted steps of a spontaneous growth and self-organization of the nanowires into two-dimensional (2D) hexagonal lattice on Pt, at intervals starting from a few hours of reaction to a highly ordered superlattice at longer times. Furthermore, it is shown that apart from long-chain acid and long-chain aliphatic amine pairs used as stabilizers, the combination of a long-chain aliphatic and a short-chain aromatic ligand in the synthesis can also be employed for the nanowire superlattices development. Interestingly, the possibility to employ different pairs allows quantitative modulation of the nanowire arrays, such as the interwire distance and the packing fraction.

Biointerface Engineering with Nucleic Acid Materials for Biosensing Applications

AbstractMolecular recognition at the biointerface plays a critical role in sensing molecular interactions (e.g., DNA hybridization) and extracellular changes, which can directly affect the detection performance of biosensors (e.g., sensitivity, specificity, and response dynamics). However, conventional sensing biointerfaces show low molecular recognition efficiency due to limited target accessibility. Engineering sensing biointerfaces to regulate the orientation, spacing, and density of surface‐confined molecular probes offer an effective approach to improve molecular recognition at interfaces. Over the last decades, biointerface engineering with nucleic acid materials has advanced the fundamental understanding of DNA hybridization kinetics and facilitated the design of improved biosensing platforms for monitoring cellular activities and diagnosing relevant diseases. This review summarizes the recent progress in nucleic acid‐based biointerface engineering. The development of nucleic acid materials that can be applied to specific diagnostic applications is briefly introduced. Then the roles of nucleic acids in tailoring the properties of nanosurfaces, cell surfaces, and macroscopic surfaces are discussed and their biosensing applications are comprehensively highlighted. Finally, future challenges and perspectives of emerging technologies and applications in the field are presented.