Low Adhesion Energy Research Articles

Research progress of multifunctional anti‐icing composites materials

AbstractThe accumulation of ice and snow will have a great impact on industry and people's lives. People usually adopted active deicing method for deicing in the past, which is characterized by high energy consumption, low efficiency, and high cost. Passive anti‐icing materials are the most widely used due to their low icing adhesion strength and energy saving, but passive anti‐icing materials tend to lose anti‐icing performance after mechanical damage or following exposure to harsh environments resembling low temperatures, high humidity. Recently, new anti‐icing materials have been rationally designed through the combination of passive and active anti‐icing, exhibiting high‐efficiency and energy‐saving anti‐icing properties. The design idea is that low surface energy polymers combine photothermal and electrothermal particles to achieve photothermal and electrothermal superhydrophobic anti‐icing. Anti‐icing materials are easily damaged after long‐term outdoor use, so the self‐healing capabilities of the materials are important. This review briefly introduces the ice formation mechanism and anti‐icing methods, focusing on the recent progress in the structural design of superhydrophobic, photothermal, electrothermal, and self‐healing anti‐icing materials. The design of the new generation of anti‐icing materials will be a combination of active and passive anti‐icing, which can achieve ideal all‐weather anti‐icing and deicing and repair the damage during long‐term use.

Development of 3D-Printed Self-Healing Capsules with a Separate Membrane and Investigation of Mechanical Properties for Improving Fracture Strength

Studies on self-healing capsules embedded in cement composites to heal such cracks have recently been actively researched in order to improve the dimensional stability of concrete structures. In particular, capsule studies were mainly conducted to separately inject reactive healing solutions into different capsules. However, with this method, there is an important limitation in that the probability of self-healing is greatly reduced because the two healing solutions must meet and react. Therefore, we propose three-dimensional (3D) printer-based self-healing capsules with a membrane structure that allows two healing solutions to be injected into one capsule. Among many 3D printing methods, we used the fusion deposition modeling (FDM) to design, analyze, and produce new self-healing capsules, which are widely used due to their low cost, precise manufacturing, and high-speed. However, polylactic lactic acid (PLA) extruded in the FDM has low adhesion energy between stacked layers, which causes different fracture strengths depending on the direction of the applied load and the subsequent performance degradation of the capsule. Therefore, the isotropic fracture characteristics of the newly proposed four types of separated membrane capsules were analyzed using finite element method analysis. Additionally, capsules were produced using the FDM method, and the compression test was conducted by applying force in the x, y, and z directions. The isotropic fracture strength was also analyzed using the relative standard deviation (RSD) parameter. As a result, the proposed separated membrane capsule showed that the RSD of isotropic fracture strength over all directions fell to about 18% compared to other capsules.

Mineral fillers for polymer nanocomposites

Traditional polymer composite materials consist of two or more phases with a clear interfacial boundary, which determines the physical and mechanical properties of plastics. The properties of nanocomposites depend on many parameters: the chemical nature of the polymer, the functionality of the modifier, the methods for obtaining the composite, and the modification of the layered silicate. Silicates are the most numerous class of minerals. They account for approximately one third of the mineral species known in nature, tk. are the most important rock-forming minerals. The use of layered silicates makes it possible to achieve a significant improvement in a number of properties of nanocomposites: a decrease in density, an improvement in the fire resistance of materials, an increase in the surface quality of products, a decrease in abrasive wear of equipment in the production of products from nanocomposites, and an increase in the recyclability of materials. Nano-reinforcement increases, among other things, rigidity and strength, and also significantly reduces the technological shrinkage of the material and improves dimensional stability. Nanostructured surfaces of such materials due to the special relief have very low adhesion energies, thus, the products acquire dirt-repellent properties, their appearance and consumer qualities are improved. In addition, the permeability of the material to gases, vapors, and odors is significantly reduced. Keywords: fillers; polymer nanocomposites; minerals.

Influence of novel shrinkage‐reducing polycarboxylate superplasticizer on the nature of calcium–silicate–hydrates

AbstractCurrently, a novel shrinkage‐reducing polycarboxylate superplasticizer (SR‐PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the influence of SR‐PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR‐PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR‐PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR‐PCA has a milder impact on C–S–H crystallinity. SR‐PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR‐PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR‐PCA is attributed to the lower adhesion energy of the C–S–H/SR‐PCA interface due to the weaker Ca–O bond strength.

Improvement of Isotropic Strength of 3D Printing-Based Self-Healing Capsules by Controlling the Position of Holes

Self-healing capable of storing two or more solutions is proposed to heal cracks by manufacturing capsules with a 3D printer to enable structural design, repeatable fabrication, and strength analysis. The Fusion Deposition Modeling (FDM) method was used to design, analyze, and produce new, widely used self-healing capsules at low cost. However, since the PLA extruded from FDM has low interlayer adhesion energy, the strength varies depending on the load angle applied to the laminated surface and concrete structure, which degrades the performance of the self-healing capsule. Therefore, this paper designed a structure with isotropic strength by controlling the direction and number of solution injection ports of capsules manufactured by the FDM PLA method. In addition, the intensity isotropy of the load applied through the compression test and ANSYS in the x, y, and z directions were verified. As a result, as the arrangement and number of holes were different, the standard deviation of strength according to the direction decreased by 24%.

Advanced quantification for single-cell adhesion by variable-angle TIRF nanoscopy

Over the last decades, several techniques have been developed to study cell adhesion; however, they present significant shortcomings. Such techniques mostly focus on strong adhesion related to specific protein-protein associations, such as ligand-receptor binding in focal adhesions. Therefore, weak adhesion, related to less specific or nonspecific cell-substrate interactions, are rarely addressed. Hence, we propose in this work a complete investigation of cell adhesion, from highly specific to nonspecific adhesiveness, using variable-angle total internal reflection fluorescence (vaTIRF) nanoscopy. This technique allows us to map in real time cell topography with a nanometric axial resolution, along with cell cortex refractive index. These two key parameters allow us to distinguish high and low adhesive cell-substrate contacts. Furthermore, vaTIRF provides cell-substrate binding energy, thus revealing a correlation between cell contractility and cell-substrate binding energy. Here, we highlight the quantitative measurements achieved by vaTIRF on U87MG glioma cells expressing different amounts of α5 integrins and distinct motility on fibronectin. Regarding integrin expression level, data extracted from vaTIRF measurements, such as the number and size of high adhesive contacts per cell, corroborate the adhesiveness of U87MG cells as intended. Interestingly enough, we found that cells overexpressing α5 integrins present a higher contractility and lower adhesion energy.

Simulated and Experimental Investigation of Mechanical Properties for Improving Isotropic Fracture Strength of 3D-Printed Capsules.

Three-dimensional (3D) printer-based self-healing capsules, embedded in cement composites, were proposed to heal cracks, as they allow for various structural designs of capsules, repeatable fabrication, and strength analysis. Out of many 3D printing methods, such as fusion deposition modeling (FDM), powder layer fusion, and PolyJet printing, FDM was used to design, analyze, and produce new self-healing capsules, which are widely used due to their high-speed, low-cost, and precise manufacturing. However, the PLA extruded in the FDM had low adhesion energy between stacked layers, which caused a degradation of the performance of the self-healing capsule, because it had different strengths depending on the angle between the stacked layers and the applied load within the concrete structure. Therefore, in this paper, specimens were produced, in accordance with ASTM specifications, using the FDM PLA method, and mechanical properties were obtained through tensile, shear, and compression tests. Additionally, the isotropic fracture characteristics of the four types of capsules were analyzed through finite element method analysis. Subsequently, the 3D-printed capsules were produced, and the fracture strength was analyzed in the x, y and z directions of the applied load through a compression test. As a result, the newly proposed capsule design was verified to have an isotropic fracture strength value of 1400% in all directions compared to conventional spherical thin film capsules

Establishing the Preferential Adsorption of Anion‐Dominated Solvation Structures in the Electrolytes for High‐Energy‐Density Lithium Metal Batteries

AbstractThe practical application of Li metal batteries (LMBs) is severely hindered by the unstable solid electrolyte interface (SEI). In this work, it is revealed that the unstable SEI mainly originates from the kinetic instability of Li+‐solvation structures in the electrolyte which can result in continuous electrolyte decomposition and nonuniform Li deposition. To address this issue, preferential adsorption of anion‐dominated solvation complexes (A‐Coms) are established by integrating preferentially adsorbed anions (NO3− and Li2S8) into the Li+‐solvation structures. In these structures, the locations of the lowest unoccupied molecular orbital energy level shift from solvents to anions, rendering a relieved electrolyte decomposition and an anion‐derived SEI formation. Meanwhile, the anions in the A‐coms preferentially adsorb on the Li metal surfaces due to their stronger chemisorption capability toward lithium metal anodes (LMAs) compared to the solvent molecules, effectively shielding solvent molecules from parasitic reaction with LMAs. Furthermore, the anion‐derived SEI exhibits high Li‐ion conductivity and low Li atom adhesion energy, which can facilitate uniform Li deposition. Consequently, this electrolyte can enable a high Li plating/stripping Coulombic efficiency of 98.5% over 500 cycles and a stable cycling under realistic testing conditions with a high‐energy‐density of 310 W h kg−1 based on a full cell configuration.

Anti-icing propylene-glycol materials

Liquid propylene-glycol (PG) has long been used as an anti-icing substance, for example, by spraying on an airplane parked in an airport. In applications, large quantities of PG flow away, which is costly and raises environmental concerns. Here we report propylene-glycol materials, including PG-gels and PG-gel/cotton composites. A PG-gel consists of PG molecules as a solvent and a polymer network. PG evaporates slowly, and the polymer network retains the PG molecules so long as the gel is not in contact with running water. Water and PG form a eutectic system with an eutectic temperature of −60 °C. When ice falls on the surface of the gel, the ice and the PG molecules compete for water molecules, and thermodynamics dictates that the ice should lose water molecules to the PG molecules, so that ice melts and water molecules dissolve in the gel. A liquid-like layer exists on the ice/gel interface, the adhesion energy between the gel and ice is low, and ice readily slides on the gel. We peel a PG-gel from ice, and measure a low adhesion energy of ∼3 Jm−2 at temperatures about −35 °C. We further demonstrate PG-gel/cotton composites as tough, anti-icing blankets. The blankets are reusable if one removes water by dehydration, and replenish PG by submerging the blanket in liquid PG.

A study on the interfacial adhesion energy between capping layer and dielectric for cu interconnects

Recently, Cu interconnect and low-k materials have been applied to reduce the interconnect resistive-capacitive delay issue. However, as the process node size is reduced to a few nanometers, high leakage currents appear through the dielectric under high electric fields. Therefore, issues of Cu diffusion at the interface between the dielectric and the capping layer have been reported. This study investigated interfacial adhesion energy change at the film level between dielectric (low-k, tetraethyl orthosilicate (TEOS)) and capping layer (SiCN, SiN) taking into account the correlation between interfacial adhesion energy and interconnect reliability. In the capping layer/low-k interface, when low-k is applied to the top layer, it shows high interfacial adhesion energy (> 34.31 ± 3.49 J/m2) due to the presence of an O-rich thin layer. But when low-k is applied to the bottom layer, due to the SiC bond, it shows low interfacial adhesion energy (< 5.60 ± 2.46 J/m2). The interface between TEOS and SiN has high interfacial adhesion energy (> 32.54 ± 1.97 J/m2) regardless of the stacking order and CMP process. It clearly shows that low-k dielectrics will affect the deterioration of the interfacial adhesion energy and O-rich layer will greatly improve the interfacial adhesion energy in dielectric/capping layers.

Electrowetting of Hydrofluoroether Liquid Droplet at a Gold Electrode/Water Interface: Significance of Lower Adhesion Energy and Static Friction Energy.

We explored the electrowetting behavior of a hydrofluoroester solvent, Novec 7100 (Novec), as a liquid droplet on a Au(111) electrode in water (0.05 M KClO4). Comparison with the electrowetting of hexadecane (HD) highlighted the significance of the lower adhesion energy and static friction energy of Novec than those of HD. The electrode potential-dependent contact angle θ of a Novec droplet showed little hysteresis. When potentials were set by means of potential steps, a Novec droplet increased its θ at more positive potentials than the potential of zero charge (pzc) of the Au(111) electrode. We found that the key factor of the electrowetting behavior for Novec is its low adhesion energy and static friction energy. The static friction energy of the oils to the Au(111) electrode surface was evaluated by a comparative analysis of the potential dependence of the interfacial tension at the solid/water interface, ΔγS/W-E curve, calculated from electrochemical surface charge data and the experimental cos θ-E curve: 2.6 mN/m for HD and 0.95 mN/m for Novec. When Br- was added in the aqueous solution to allow its adsorption on the Au surface surrounding a Novec droplet, the potential of maximum cos θ was shifted to negative. Overall, although the Novec droplet showed a narrower range of θ change than a HD droplet, the Novec droplet seldom got stuck to the surface as far as potential step was used, reflecting the narrower plateau region of θ near the pzc. Also, the specific adsorption of a coexistent anion was a significant factor of θ. This work has featured the significance of a slippy droplet on an electrode surface, giving an impact on the technology of microfluid transportation control by electric potentials.

Wetting and adhesion energy of droplets on wettability gradient surfaces

Wettability gradient surfaces can be used for heat and mass transfer in many fields, which has aroused extensive interest of research. However, since numerous studies only focused on the surfaces with identical microstructures, the wetting and adhesion energy of droplets on wettability gradient surfaces are still unclear. In this work, three types of microstructured surfaces with gradient wettability were fabricated via photolithography and etching methods. We found that the contact angle, contact angle hysteresis and critical sliding angle will increase with area fraction. Meanwhile, the gradient microstructures will affect the triple line and wetted area of droplets. In addition, it is found that the critical sliding angle depends on not only the droplet volume but the size and types of microstructures, which is consistent with our force analysis. Based on the morphological characteristics and actual wetted area of droplets, an adhesion energy model for microstructured surfaces with gradient wettability is proposed. The model is also verified by other types of wettability gradient surfaces, which may be helpful to design wettability gradient surfaces with low adhesion energy for practical applications.

Interfacial properties of pure and doped CdS/graphene composites: CdS(0001)/graphene and a CdS/graphene bilayer

The photocatalytic performance of CdS can be improved by pairing it with graphene, and new CdS/graphene nanoarchitectures offer the potential to optimize this enhancement. In this work, we explore the interfacial properties of CdS(0001)/graphene and a novel CdS/graphene bilayer using density functional theory (DFT), and examine whether doping with B and N can strengthen interfacial adhesion. We first determine an appropriate DFT method for bulk CdS and graphene, and study the properties of the isolated components. The CdS/graphene bilayer is then optimized and found to exhibit high interplanar distances and low adhesion energies, which are indicative of interfacial adhesion via dispersion. Doping the graphene layer with B and N does not significantly modify the strength of adhesion, but doping does enable modulation of the band edge and Fermi level alignments, which affect the driving force for photoexcited charge transfer. The CdS(0001)/graphene interface is also optimized and found to be similarly adhered via dispersion interactions. Here, doping with B considerably strengthens adhesion in the interface, due to chemical interactions between B and a surface Cd atom, while doping with N had no effect.

Blister Test as Method of Measuring Adhesion of Solids on a Flat Surface

The adhesion between coating and a flat metal surface hasbeen investigated by measurements. The setup is based on theformation of a blister by injecting nitrogen gas under pressurebetween the coating and the substrate. The adhesion energy isdetermined by recording the pressure as a function of therecorded blister radius development. A laser is moved over theblister in 2D with two programmable step engines to measurethe blister profile and thereby the radius of the blister betweensuccessive pressure increases. The design and operation of theinstrument are described and an evaluation of its performanceand limitations is given. The method could be useful for accuratemeasurement of adhesion of many types of surface coatings tometal and, possibly, to other substrates, as well as for studies ofthe various factors that influence adhesion. A better accuracy ofthe laser for measuring the blister profile would improve thesetup.We treated aluminium surfaces in different manners (sandpaper, polishing and blowing using glass particles) but found nosignificant impact on the adhesion energy between the x-linkedcoating layer and the metal. The adhesion energy measurementshowever have a large scatter. The coating layer that was not xlinkedhad a much lower adhesion energy.

Dislocation emission and crack propagation during thin film buckling on substrate

The buckling of a gold thin film deposited on a rigid substrate has been numerically investigated by means of static molecular dynamics simulations. Three different regimes of deformation have been identified depending on the values of the adhesion energy of the film on its substrate (Γint). For low adhesion energy, the buckling and gliding through dislocation emission into the interface have been observed. For intermediate values of Γint, the dissociation of the interfacial dislocations into the film leads to the formation of a Lomer–Cottrell lock that stops the buckle extension, promoting thus the propagation of a crack accompanied by the emission of dislocations. It results in the formation of a twin. For large values of Γint, the kinking of the interfacial crack has been evidenced along with dislocation nucleation at its tip leading to twins again. Finally, the different evolutions of the film have been summarized in a “behavior” diagram displayed in the plane of applied strain and adhesion energy variables.

Indoor experiments of dust deposition reduction on solar cell covering glass by transparent super-hydrophobic coating with different tilt angles

Dust deposition on solar photovoltaic (PV) panels would greatly reduce the PV output efficiency, especially in dusty regions. This paper investigated dust deposition reduction on solar cell covering glass by transparent super-hydrophobic coating under different PV tilted angles. The macroscopic and microscopic dust deposition patterns, dust deposition density, spectral transmittance of covering glass and PV efficiency reduction caused by dust deposition were studied and analyzed. The results showed that dust deposition on the glass surface can be greatly reduced by super-hydrophobic coating due to the low adhesion energy. The super-hydrophobic coating has a better performance on dust deposition reduction compared with hydrophobic coating. The deposition density on the glass with super-hydrophobic coating is just 44.4%, 28.6% or 11.2% of the bare surface for tilt angle θ = 30°, θ = 45° or 60°, respectively. The spectral transmittance of coated glass and the PV efficiency are obviously higher compared with bare glass case after dust deposition. Moreover, the self-cleaning coating has better performance for large tilt angle and poly-crystalline silicon PV cell. The performance of super-hydrophobic coating on dust deposition reduction is similar between the test dust and the real dust obtained from Guangzhou, China.

Formation of Surface Deposits on Steel and Titanium Aviation Fuel Tubes under Real Operating Conditions.

In this study, stainless steel and titanium (Ti) tubes obtained from a turbofan engine after the end of its lifetime were analyzed in order to compare the amount of pyrolytic coke present and its influence on the parent, base material. Various analytical techniques including microhardness and topographical evaluations, optical emission spectrometry (OES), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were applied. On steel surfaces, a thick pyrolytic coke deposition layer consisting of carbon and oxygen and also containing elements from the tube material, fuel, and fuel additives was found. The concentration of elements from the pyrolytic coke continuously decreased with distance from the surface of the deposit, while the concentrations of elements from the tube material continuously increased, with the concentrations of elements from the fuel and the fuel additives being relatively constant. With ultrasonic cleaning in distilled water, most of the deposits could be removed. Only carbon-rich patches with a thickness of more than 300 nm remained adhered to the surface and/or had diffused into the original material. On Ti surfaces, the thickness of the C-rich fuel deposit layer was significantly thinner as compared to that on the stainless steel; however, the surface was covered with an ∼3 μm-thick oxide layer, which consisted of elements from the fuel additives. It is believed that the beneficial properties of Ti covered with a thin layer of TiO2, such as low adhesion and/or surface energy, have promoted different deposition mechanisms compared to those of stainless steel and thus prevented pyrolytic coke deposition and the related material deterioration observed on stainless steel.

Interfacial fluid transport is a key to hydrogel bioadhesion

Attaching hydrogels to soft internal tissues is a key to the development of a number of biomedical devices. Nevertheless, the wet nature of hydrogels and tissues renders this adhesion most difficult to achieve and control. Here, we show that the transport of fluids across hydrogel-tissue interfaces plays a central role in adhesion. Using ex vivo peeling experiments on porcine liver, we characterized the adhesion between model hydrogel membranes and the liver capsule and parenchyma. By varying the contact time, the tissue hydration, and the swelling ratio of the hydrogel membrane, a transition between two peeling regimes is found: a lubricated regime where a liquid layer wets the interface, yielding low adhesion energies (0.1 J/m2 to 1 J/m2), and an adhesive regime with a solid binding between hydrogel and tissues and higher adhesion energies (1 J/m2 to 10 J/m2). We show that this transition corresponds to a draining of the interface inducing a local dehydration of the tissues, which become intrinsically adhesive. A simple model taking into account the microanatomy of tissues captures the transition for both the liver capsule and parenchyma. In vivo experiments demonstrate that this effect still holds on actively hydrated tissues like the liver capsule and show that adhesion can be strongly enhanced when using superabsorbent hydrogel meshes. These results shed light on the design of predictive bioadhesion tests as well as on the development of improved bioadhesive strategies exploiting interfacial fluid transport.

Low-energy phase boundary pairs and preferred crystallographic orientations of olivines in nanometer-sized ultrapotassic fluid inclusions of Aykhal diamond

The healed internal conjugated cleavages at the core of Aykhal octahedral diamond sample AH2 were decorated with {111}dia-facetted ultrapotassic fluid/melt inclusion pockets containing nanosized graphite, phlogopite and olivine (Fo92) inclusions. These olivines are either rounded in pockets with ample fluid, or facetted by the {111}dia mold in the pockets with a fluid film. Transmission electron microscopy revealed two distinct crystallographic characteristics of olivine inclusions: (1) pronounced crystallographic texture of olivines grouped in specific diamond domain, and (2) frequent parallelism or sub-parallelism of specific low-energy faces of the two phases, mainly (010)ol, {120}ol, (001)ol and {111}dia, {110}dia, {100}dia in the order of decreasing preference, forming prominent (010)ol/{111}dia, (010)ol/{110}dia, (001)ol/{110}dia, {120}ol/{111}dia, and {120}ol/{110}dia low-energy phase boundaries with thin liquid film of 1–2 nm in between. These findings not only testify to the extremely low adhesion energies of olivine-diamond boundary pairs, but also imply that, in the presence of a fluid phase, the interfacial energetics and the energetically favored crystallographic orientations of olivine inclusions in diamond can be controlled simply by the settlement/attachment of low-energy facets of olivine crystals precipitating from the parental fluid upon the low-energy {111}dia or {110}dia surfaces of diamond. Such interfacial energetics control and the resultant low-energy boundary pairs are characteristically distinct from the common topotaxy or epitaxy between oxide/silicate mineral pairs, but are in a sense like the Van der Waals heteroepitaxy in artificial systems.

Mechanics of spontaneously formed nanoblisters trapped by transferred 2D crystals

Layered systems of 2D crystals and heterostructures are widely explored for new physics and devices. In many cases, monolayer or few-layer 2D crystals are transferred to a target substrate including other 2D crystals, and nanometer-scale blisters form spontaneously between the 2D crystal and its substrate. Such nanoblisters are often recognized as an indicator of good adhesion, but there is no consensus on the contents inside the blisters. While gas-filled blisters have been modeled and measured by bulge tests, applying such models to spontaneously formed nanoblisters yielded unrealistically low adhesion energy values between the 2D crystal and its substrate. Typically, gas-filled blisters are fully deflated within hours or days. In contrast, we found that the height of the spontaneously formed nanoblisters dropped only by 20-30% after 3 mo, indicating that probably liquid instead of gas is trapped in them. We therefore developed a simple scaling law and a rigorous theoretical model for liquid-filled nanoblisters, which predicts that the interfacial work of adhesion is related to the fourth power of the aspect ratio of the nanoblister and depends on the surface tension of the liquid. Our model was verified by molecular dynamics simulations, and the adhesion energy values obtained for the measured nanoblisters are in good agreement with those reported in the literature. This model can be applied to estimate the pressure inside the nanoblisters and the work of adhesion for a variety of 2D interfaces, which provides important implications for the fabrication and deformability of 2D heterostructures and devices.