Surface Energy Materials Research Articles

The effect of dislocation pile-up on microcrack initiation in microcrystalline materials in the hydrogen environment

In this paper, hydrogen (H) induced microcrack initiation in the first stage of crack propagation is studied. Based on the knowledge of fracture mechanics and discrete distributed dislocation method, the interaction model between hydrogen atoms at crack tip and dislocation source, the grain boundary (GB) penetration model and microcrack initiation criterion are established, and the microcrack initiation mechanism caused by dislocation pile-up near the grain boundary 2 (GB2) is studied. Meanwhile, the mechanism of dislocation synthesis (DS) caused by dislocation stacking is studied. The results show that hydrogen atoms promote the emission of dislocations at the crack tip. The distribution of H atoms at the crack tip (CT) leads to an increase in the number of dislocations penetrating the grain boundary, and the number of dislocation pile-up in the second phase grain increases. In the hydrogen environment, the number of dislocation pile-up near GB2 increases, resulting in a large stress concentration near GB2, which makes microcracks more likely to occur. At the same time, H can decrease the surface energy of materials, making materials more prone to brittle fracture. The study of hydrogen induced crack initiation is helpful to understand and control the impact of H on the performance and reliability of metal materials, which plays a crucial role in improving the working efficiency and service life of metal materials.

Thermal Surface Properties, London Dispersive and Polar Surface Energy of Graphene and Carbon Materials Using Inverse Gas Chromatography at Infinite Dilution.

The determination of these surface properties is carried out using inverse gas chromatography at infinite dilution, which leads to the retention volume of organic solvents adsorbed on solid surfaces. This experimental and fundamental parameter actually reflects the surface thermodynamic interactions between injected probes and solid substrates. The London dispersion equation and the Hamieh thermal model are used to quantify the London dispersive and polar surface energy of graphenes and carbon fibers as well their Lewis acid-base constants by introducing the coupling amphoteric constant of materials. The London dispersive and polar acid-base surface energies, the free energy of adsorption, the polar enthalpy and entropy, and the Lewis acid-base constants of graphenes and carbon materials are determined. It is shown that graphene exhibited the highest values of London dispersive surface energy, polar surface energy, and Lewis acid-base constants. The highest characteristics of graphene justify its great potentiality and uses in many industrial applications.

Facile preparation and application of ternary hybrid of POSS/DOPO/F macromolecular as highly-effective epoxy modifier

In order to easily achieve the multifunctionality of epoxy resin, this paper designs and synthesizes a ternary hybrid copolymer containing POSS/DOPO/F. This method not only facile combines POSS with DOPO, but also introduces F element to further reduce the surface energy of epoxy composite materials. Research has found that the POSS/DOPO/F ternary hybrid copolymer can achieve a UL-94 flame retardant rating of V-0 with just 5 wt% of the modifier, and the limit oxygen index of epoxy composites is 32% (23.1% higher than pure epoxy resin). The residual char after combustion is denser and the carbonization rate is higher. Furthermore, we conducted an in-depth analysis of the flame retardant mechanism of POSS/DOPO/F ternary hybrid copolymer epoxy composites using TGA-FTIR technology and EDS. In addition, the introduction of ternary hybrid polymers effectively improves the mechanical properties of epoxy composite materials and significantly reduces the surface energy of the composite materials.

Effects of fluorosilane addition on polyurethane electrospun membranes with waterproof and breathable performance

Waterproof and breathable fibrous membrane is a new type of polymer functional material widely used in outdoor protection, sports equipment, industrial production, and other fields. To impart waterproof ability and breathability, a common practice is to modify the electrospun membrane with low surface-energy materials, such as fluorosilane. However, when directly added to the electrospinning solution, the effects of fluorosilane on the property of the prepared membrane have been scarcely reported. Herein, we prepared the electrospun polyurethane membrane by adding two types of fluorosilane into the polyurethane solution. The effects of fluorosilane type and concentration on the conductivity and viscosity of the electrospinning solution were investigated. Moreover, the prepared polyurethane/fluorosilane fibrous membranes are analyzed in terms of their surface morphology, structure, water contact angle, breathable performance, and mechanical properties. Results show that the dual effects of fluorosilane content exert an opposing influence on the jet drawing process, which yields a minimum fiber diameter when the fluorosilane content is 20%. Under this condition, the membrane shows the highest water vapor transmission rate (10.4 kg/(m2·d). In addition the membranes have the maximum water contact angle (138°) and breaking strength (12 MPa) when the fluorosilane content is 40%. This study provides insights into fabricating electrospun waterproof and breathable membranes in equipment for outdoor sports and protection.

Effect of material composition on the action of surface active medium in ultra-precision microcutting

Ultra-precision diamond turning (UPDT) is an extensively adopted technology in optical applications owing to the nanometric surface finish and excellent form tolerance guaranteed on metallic materials. Coolants such as kerosene, isoparaffin etc. are broadly used in UPDT to reduce the friction at tool-workpiece interface for ultimately ensuring optical quality parts. However, the greater emphasis on sustainable manufacturing nowadays demand alternate approaches for minimizing cutting forces and improving the surface finish. The application of a surface active medium (SAM) over the workpiece surface prior to UPDT can be a befitting choice as it can induce Rehbinder effect on materials thereby minimizing cutting forces. Nevertheless, the performance of SAM in UPDT process with reference to material specific properties has not been widely explored in literature. The present study investigates the role of Rehbinder effect in controlling the material surface energy during UPDT of ductile materials. The surface integrity and force analysis indicate that the SAM action is significantly different for the parent metal (Cu) and alloy (Brass) under consideration. Moreover, the chip morphology inspection highlighted that SAM facilitates easier crack initiation and fracture in Cu unlike Brass. The results were further confirmed by conducting experiments on pure Zinc. Thus, the present study establishes the varying effectiveness of SAM towards material specific elemental composition.

Justification of the effect of the regularities of the flow of nanotribological processes in the materials of joint parts on the increase of wear resistance, reliability and efficiency of the functioning of machines and mechanisms

The article elucidates the essence of nanotribological processes in the materials of conjugation of samples of parts by the methods of the surface force apparatus, scanning tunneling and atomic force microscopy. The substantiation of the mechanisms of their occurrence is given by the methods of molecular dynamics and classical contact mechanics. Attention is paid to dry adhesive and contactless dynamic friction of conjugated samples, physical processes in "sticking-sliding" tribocontacts, adhesive effects, etc. The values of the lateral and normal forces acting on the probe were analyzed. The probe was considered as a collection of point particles of concentrated mass with a multiatomic structure of the material. The contact and movement of the probe with the surface of the sample was considered in the "probe-surface" system with minimal potential energy and lateral load and taking into account conservative and dissipative forces.
 The effect of "sticking-sliding" is substantiated with the help of the apparatus of surface forces. The atomic periodicity of the effect is explained on the basis of the model of the formation and breaking of adhesive bonds and the "atom-magnet" model. It is shown that the patterns of "sticking-sliding" processes can be determined by using the parameters of shear stress and specific work of adhesion.
 It is advisable to use the Johnson-Kendall-Roberts theory to explain the elastic adhesive contacts, and the Deryagin-Mullier-Toporov theory for the residual friction force and probe separation force.
 It is shown that there is a significant connection between friction and adhesion processes. The correlation between the macroscopic value of the surface energy of materials and their shear modulus for homogeneous contacts was determined.
 On the basis of adhesive effects and the effect of "sticking-sliding", it is possible to control frictional forces and create favorable conditions for their absence, which gives grounds for obtaining high wear resistance of tribo-joints of parts, their reliability and maximum efficiency of the functioning of machines and mechanisms

Molecular dynamics study on wetting behavior of aluminum plates with different surface energies by microstructure difference

Wettability is the main factor that affects the self-cleaning and corrosion resistance of metal surfaces. The main factor that affects wettability is the change of surface microstructure and surface energy of metal material. When modifying metals, it is necessary to master their wetting behavior to obtain the required performance surface. In this paper, the wetting behavior of liquid droplets on smooth, square, papillary and nail-shaped surfaces with different surface energies was studied systematically by molecular dynamics simulation. The results show that the solid–liquid interaction factor is negatively correlated with the surface contact angle of aluminum plate. When the solid–liquid interaction factor is greater than the droplet potential energy parameter, the nail-shaped surface has the largest solid–liquid contact area and droplet centroid displacement rate due to its large roughness, and the surface hydrophilicity is the best; When the solid–liquid interaction factor is close to the droplet potential energy parameter, the nail-shaped surface has the smallest solid–liquid contact area and droplet centroid displacement rate due to its large roughness, and realizes the transition from neutral to hydrophobic; When the solid–liquid interaction factor is less than the droplet potential energy parameter, the papillary surface has the smallest solid–liquid contact area and droplet centroid displacement rate due to its small solid–liquid area fraction, thus realizing the transition from hydrophobicity to superhydrophobicity. The simulation results of this study are consistent with the classical theoretical calculation and experimental results, which reveals the interaction between metal surface wettability and surface energy and surface morphology.

Research on the Performance of Superhydrophobic Cement-Based Materials Based on Composite Hydrophobic Agents.

The utilization of a novel monolithic superhydrophobic cement material effectively prevents water infiltration and enhances the longevity of the material. A method for improving superhydrophobic concrete was investigated with the aim of increasing its strength and reducing its cost by compounding superhydrophobic substances with water repellents. The experimental tests encompassed the assessment of the compressive strength, contact angle, and water absorption of the superhydrophobic cementitious materials. The findings demonstrate that an increase in the dosage of isobutyltriethoxysilane (IBTES) progressively enhances the contact angle of the specimen, but significantly diminishes its compressive strength. The contact angle of SIKS mirrors that of SIS3, with a superior compressive strength that is 68% higher. Moreover, superhydrophobicity directly influences the water absorption of cementitious materials, with a more pronounced superhydrophobic effect leading to a lower water absorption rate. The water absorption of cementitious materials is influenced by the combined effect of porosity and superhydrophobicity. Furthermore, FT-IR tests unveil functional mappings, such as -CH3 which can reduce the surface energy of materials, signifying successful modification with hydrophobic substances.

Quantitative prediction of surface energy of high-entropy-alloys based on intrinsic descriptors

A wide range of surface properties of interest are closely correlated to the surface energy of metallic materials. High-entropy-alloys (HEAs) are known for their novel mechanical and physical properties, while their inherent surface complexity hinders the quantitative description of the structure-property relationship. In this work, we utilize the surface electronic descriptor Жsurface, which is based on the period number, group number, valence-electron number and electronegativity of surface atoms, to point-to-point describe the non-local surface environment of complex HEA surfaces with different geometries. We find that surface energy is strongly correlated with the atoms in the HEA single surface layer, while the bulk phase atoms of HEAs slightly affect the linear relationship only when the bulk phase is in the low entropy state, and different geometries mainly lead to the overall shift of surface energy distribution. This model quantitatively correlates surface energy with the intrinsic properties of IrRuRhPdPt, NbMoTaTi and NbMoTaTiV HEAs, and could be helpful to fine-tune the surface energy in materials design. Moreover, our model allows rapid screening of potentially interesting materials through a large phase space of HEA surfaces, owing to that all the parameters are easily accessible from the periodic table of elements.

Predicting crack growth of paving materials under indirect tensile fatigue loads

Cracking of paving materials affects the reliability and safety of pavement structures, and indirect tension (IDT) test is commonly used to investigate the cracking behavior of the paving materials. However, the existing studies usually adopted a reduced modulus or strength to indirectly quantify cracking damage under the IDT fatigue loads. A direct analysis method for the crack growth under the IDT fatigue loads is still missing. The objective of this study is to propose a crack growth prediction model under the IDT fatigue loads based on continuum damage mechanics (CDM), which can directly quantify and predict the crack growth of the paving materials. Two types of paving materials, cement-treated aggregates and asphalt mixtures, were investigated. A damage density model based on CDM was proposed to quantify the crack growth under the IDT fatigue loads. The model coefficients are obtained by the IDT horizontal tensile stress, material surface energy, resilient modulus, and the size of the IDT specimen. The surface crack length of the IDT specimen is obtained using the solved damage density with introducing a crack depth ratio. Results show that the cement-treated aggregates show relatively more brittle cracking where the cracks are penetrative and going through the whole thickness of the IDT specimen. In contrast, the asphalt mixtures exhibit more ductile cracking where multiple cracks present and are nonpenetrative. The cracks of the asphalt mixture penetrate only 48% and 46% of the specimen thickness when the IDT fatigue loads are 540 kPa (1 Hz) and 700 kPa (10 Hz), respectively. The damage density calculated by the CDM-based model can accurately predict the crack lengths for both the cement treated aggregates and the asphalt mixtures, which are found consistent with the measured crack lengths from the IDT tests. This study provides a mechanics model for determining the crack growth under the IDT fatigue loads that can serve as a tool for evaluating the fatigue crack resistance of the paving materials like the asphalt mixtures and cement treated aggregates.

Optimization preparation and durability analysis of abrasion resistant-superhydrophobic cementitious material

In this study, stearic acid (SA), polymehtylhydrosiloxane (PHMS) and attapulgite (ATP) were mechanically mixed in absolute ethanol firstly. After that the mixture was coating on the surface of cementitious material to prepare abrasion resistant-superhydrophobic cementitious material. Through experiments and theoretical analyses, the effects of different coating methods and SA content on superhydrophobic and abrasion resistant properties were studied. Moreover, the impermeability and erosion resistance of abrasion resistant-superhydrophobic cementitious material under different working conditions were also investigated. The results indicate that coating method has a great influence on superhydrophobic properties. Compared with dip coating method, the material prepared by one-step spraying method has better superhydrophobic performance. The results also show that the reasonable addition of SA could significantly improve abrasion resistant of the material. In addition, the study indicates that with the increase of roughness, the surface energy of abrasion resistant-superhydrophobic cementitious material dramatically decreases. The surface energy of coating containing 2 wt% ATP is only 26.84% of the coating without any ATP. Furthermore, permeability and electrochemical experiments show that the abrasion resistant-superhydrophobic cementitious material prepared by one-step spraying method has excellent impermeability and erosion resistance.

Universal strategy for constructing antibioadhesive and robust coatings for wood

The demand for surface antibioadhesion of wood, the most widely used material for interiors, has increased due to health concerns. For achieving antibioadhesion, the surface energy of wood materials must be reduced and their micro/nanostructure roughness must be increased. Inspired by lotus leaves, poly(pentafluorophenyl isocyanide) (PFPI)-grafted wood (wood-g-PFPI) with micro/nanostructure roughness and low surface energy was developed by grafting PFPI into the wood structure at the molecular level via thiol–ene click chemistry. The chemical structure, morphology, and water contact angle of wood-g-PFPI were characterized via Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Wood-g-PFPI10 exhibited excellent hydrophobicity (162°), antibacterial adhesion (Staphylococcus aureus and Escherichia coli), antifriction as well as self-cleaning properties, and biocompatibility owing to the increased surface roughness of the ring helical structure of the grafted PFPI. This method makes full use of the molecular characteristics of wood, so it can also be transferred to all the cellulosic substrates, such as fabric, paper and so on. Regardless of the size and space constraints of the substrate, this modification method has the potential for antibioadhesion and other applications of helical polymers.

Corrosion-resistant superhydrophobic films on galvanized steel by one-step electrodeposition

A simple one-step electrodeposition method is proposed to fabricate corrosion-resistant superhydrophobic films on hot-dip galvanized steel without using low surface-energy materials. The effects of electrodeposition time on surface morphology, surface composition, surface roughness, wettability, and corrosion resistance of the electrodeposited zinc films were investigated. The results revealed that the morphological structures and roughnesses of the deposited zinc films were varied by the electrodeposition times. The roughened zinc films naturally reduced their surface energy during storage for 10 days as the formation of functional groups, transforming them to superhydrophobic and/or nearly superhydrophobic. The electrodeposited superhydrophobic films significantly enhanced the corrosion resistance of the hot-dip galvanized steel. Among them, the 20 min electrodeposition time gave the appropriate morphology and roughness to achieve a superhydrophobic surface with the optimum corrosion inhibition property.

Isotherm and kinetic of adsorptive Purolite S108 mixed matrix membrane for boron adsorption

Excess boron in the water may cause adverse effects on humans, animals, and plants. An adsorptive mixed matrix membrane (MMM) containing Purolite S108 resin as an active filler was developed in the current study to remove boron from water. A flat sheet membrane was fabricated from a dope solution of 20 wt% polyethersulfone (PES), 5% polyvinylpyrrolidone, 1% Purolite S108 and 74% n-methyl-2-pyrrolidone using a phase inversion process. The membrane was characterized by Field Emission Scanning Electron Microscope (FESEM) and porosity. Both the pristine PES and Purolite S108 MMM membranes displayed an asymmetric structure with different macrovoid patterns at the bottom. The larger macrovoid at the bottom of the pristine PES membrane suggested a faster demixing rate during the membrane phase inversion process. In contrast, the Purolite S108 MMM showed a teardrop macrovoid that formed due to changes in the membrane material's surface energy or chemical composition. These changes created areas where the membrane was less wettable, causing water droplets to form instead of spreading out. Furthermore, the Purolite S108 MMM membrane exhibited slightly higher porosity than the pristine PES membrane, with porosity values of 43.27% and 38.05%, respectively.The adsorption isotherm and kinetic of the Purolite S108 MMM were evaluated using an aqueous boron solution. Three two-parameters adsorption isotherms were tested: Langmuir, Freundlich and Temkin. Purolite S108 MMM is best fitted to the Langmuir adsorption isotherm with the maximum binding capacity of 1.4349 mg B/g membrane. Pseudo-first order (PFO) and pseudo-second-order (PSO) models were tested in the kinetic experiment. The boron uptake by the Purolite S108 MMM followed a PFO kinetic model. The adsorption isotherm and kinetic data of the Purolite S108 MMM are essential for further optimizing the adsorptive membrane operation for boron removal.

Calculating the Surface Layer Thickness and Surface Energy of Aircraft Materials

The surface layer determines the physical properties of aviation materials and, based on these properties, the calculation of surface energy anisotropy can be implemented. Moreover, the value of the surface energy determines the service time and the destruction of aircraft structures surface layer, while the surface layer thickness determines the distance at which this process usually takes place. In this work, a new atomically smooth crystal empirical model is built without considering the surface roughness. This model can be used to theoretically predict the surface energy anisotropy and surface layer thickness of metals and other compounds, in particular the aviation materials. The work shows that the surface layer of an atomically smooth metal, like other compounds, consists of two nanostructured layers: d(I) and d(II). Having sufficient accuracy, the proposed model would allow the prediction of aviation materials performance properties without the need for ultrahigh vacuum or other complicated theoretical methods to analyze the surfaces of nanosystem atomic structures.

Multidimensional evaluation of highly durable scalable and seamlessly integrated fiber-based electrodes for wearable applications

The emergence of “green” electronics is a response to the pressing global situation where conventional electronics contribute to resource depletion and a global build-up of waste. For wearable applications, green electronic textile (e-textile) materials present an opportunity to unobtrusively incorporate sensing, energy harvesting, and other functionality into the clothes we wear. However, the robustness and functional longevity of the majority of e-textiles made of green electronic materials are not sufficient. Here, we demonstrate knittable, washable, durable, electroactive fibers produced through a scalable roll-to-roll coating process using a biocompatible polymer:polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) ink. In order to analyze the fiber's wetting behavior prior to coating, surface energy of synthetic fiber materials was evaluated. For the first time, the Owens, Wendt, Rabel and Kaelble (OWRK) approach along with the Washburn method were used to determine apparent surface energies of fiber materials and calculate the work of adhesion and interfacial tension between the conductive ink and fiber substates. The coated fibers developed in this study were successfully knitted into 3D textile electrodes using an industrial-scale knitting machine and machine washed for 60 times without any deterioration in performance to collect electrocardiogram signals. The wash durability of the coated fibers in combination with the scalable coating process make these fibers suitable to be integrated into smart textiles and wearable products for various application.

Surface properties of molds for powder injection molding and their effect on feedstock moldability and mold adhesion

The surface energy of various mold materials for low-pressure powder injection molding was evaluated using values of contact angles (Owens–Wendt method), and correlated with the feedstock moldability and mold adhesion. The surface tension of the binder used to formulate a metallic-based feedstock was also measured in the molten state at a typical injection temperature using the pendant drop technique. Real-scale injection tests were performed into metallic and polymeric mold cavities to assess the feedstock moldability and its adhesion with the mold surfaces that were compared with theoretical predictions obtained from the surface energies values. The results confirmed that the adhesion was significantly affected by the interfacial energy between the mold and the binder—in this case, the metallic mold exhibited low adhesion as compared to the polymeric mold. It was finally demonstrated that the adhesion phenomenon is only related to the surface properties of the mold (i.e., they are not related to the solidification rate)—in this case, a gold-coated polymeric mold produced the moldability of a polymeric mold and the adhesion properties of a metallic mold, which translated into a high moldability potential, with no resulting adhesion of the feedstock with the mold.

Zincophilic Design and the Electrode/Electrolyte Interface for Aqueous Zinc‐Ion Batteries: A Review

AbstractAqueous zinc‐ion batteries (ZIBs) are limited in energy storage by the persistent Zn dendrites, which is a major bottleneck preventing the commercial application of rechargeable aqueous zinc‐ion batteries. The dendritic problems associated with Zn metal anodes can lead to rapid performance degradation, failure and even safety risks of the battery. Zincophilicity of the electrode/electrolyte interface is critical to the stable and safe operation for aqueous ZIBs. In this review, we discuss that zincophilicity can be regulated by tuning the chemical interactions of material surface energy with zinc metal, emphasizing the importance of zincophilic design for improving the electrochemical performance of zinc electrodes. Advances in optimization strategies for the zincophilic zinc metal anode/electrolyte interface are summarized. Challenges and prospects for further exploration and balance of zincophilicity of the anode/electrolyte interface are presented, which are expected to promote in‐depth research and practical applications of advanced aqueous zinc ions.

Conditions for and Characteristics of the Dispersion of Gel Fuel Droplets during Ignition

We formulated and experimentally proved a hypothesis on the causes of dispersion (puffing and microexplosion) of binary fuel droplets, including those in the composition of gel fuels. This hypothesis is based on the concepts of wetting thermodynamics and the theory of the two-component surface energy of substances and materials. An effective and reliable criterion was established that allowed the assessment of the possibility of the onset of puffing and microexplosion during the high-temperature heating of binary liquids. Microexplosions were found to occur only when isothermal conditions were necessarily reached at the liquid–liquid interface during the mixing of mutually insoluble components, provided that one component had to be polar, and the second had to be dispersive. In addition, it was necessary to provide external heating conditions under which the value of the surface free energy of the liquid–liquid interface formation tended to zero.

Monte Carlo Sensitivities and Performance of Woven Deployable Entry Systems

A material response model is developed for the determination of erosion rates and thermal response of woven materials to enable accurate thermal protection material sizing and future missions to Venus and giant planets. The stagnation-point thermal response is evaluated using the model developed in Icarus, a material response finite volume solver. A Monte Carlo global sensitivity analysis is further performed using a stand-alone Python wrapper script developed to determine the interactions between key parameters in the material surface energy balance of the one-dimensional simulation, such as the convective blowing correction parameter and weave material properties. The time-accurate material response for the dual-weave erosion and surface temperatures show good agreement with stagnation flat face arcjet tests involving time-varying aeroheating–cooling cycles. The high-fidelity Monte Carlo sensitivity analysis technique was used to address challenges in thermal protection sizing for the Adaptive Deployable Entry and Placement Technology (ADEPT) system, a low ballistic coefficient hypersonic decelerator. The results provide new correlations for such weaves involving carbon–air equilibrium oxidation and wall enthalpy imposition through a B-prime formalism. Through the multivariate regression analyses and uncertainty rankings performed, only two properties were found to largely contribute to the transient thermal response of the gore, with emissivity contributing up to of the total output uncertainty at the front face and at the back face.