Adhesion Strength Research Articles

Substrate modification for high performance CrAl/CrAlBN multilayers coated TiCN-based cermet through plasma nitriding

The plasma nitriding process was conducted on a TiCN-based cermet that had been coated with a multilayer CrAl/CrAlBN coating deposited via cathodic arc. The intensity of the plasma nitriding was modified by adjusting the anode current of the ionization source. To investigate the interface conditions, techniques such as electron probe X-ray microanalysis, electron backscatter diffraction, and transmission electron microscopy were employed. The results indicated that increasing the anode current led to the formation of a thicker nitrided layer and an increase in the texture coefficient of the (111) plane. Specifically, at an anode current of 200 A, the lattice mismatch degree at the TiCN/CrAlN interface decreased from 16.4 % to 3.7 %, resulting in the formation of a nearly coherent interface. The hardness, adhesion strength, and H/E ratio of the coating reached their peak values, and the coated cutting tool exhibited optimal cutting performance when machining the GH4149 superalloy.

Designing the regularity of biodegradable copolyester for sustainable hot-melt adhesives: Adhesion, removability, and biodegradability

Recent research has increased in eco-friendly hot-melt adhesives as alternatives to conventional commercial hot-melt adhesives. However, there have been limitations in terms of removability and biodegradability. This study addresses these issues by designing a novel molecular structure for a single polymer, resulting in a sustainable hot-melt adhesive that offers strong adhesion, clear removability, and high biodegradability without additional additives. By varying the ratio of alcohol monomers 1,4-butanediol (BD) and ethylene glycol (EG) during polymerization, we synthesized poly(butylene adipate-co-butylene terephthalate-co-ethylene adipate-co-ethylene terephthalate) (PBEAT) with four block segments. We increased the open time by reducing the regularity of the molecular structure, controlling crystallization behavior, and inhibiting polymer chain packing. This improvement in wettability with the adherend allowed us to achieve a lap shear adhesion strength of 3.18 MPa. Additionally, we proposed a debonding mechanism based on the correlation between the crystallization temperature (Tc) block copolymer's and shear adhesion failure temperature (SAFT), demonstrating the removability of the prepared hot-melt adhesive. Finally, analyses of hydrolysis, enzymatic degradation, and biodegradation in compost confirmed that reduced crystallinity enhances biodegradability. PBE30AT, exhibiting the strongest adhesion strength, achieves complete degradation in compost within 20 days, faster than neat poly(butylene adipate-co-terephthalate) (PBAT). This research offers a novel and practical approach to enhancing the potential and expandability of sustainable adhesives by tailoring the molecular structure of the polymer.

Robust photothermal anti/de-icing hydrophobic coating based on polydopamine (PDA) composition

The hydrophobic soft coating has low ice adhesion strength and hydrophobic stability in low-temperature and high-humidity environments, which is crucial for preventing ice formation on infrastructure and transportation systems. However, creating mechanically durable hydrophobic soft coatings using simple methods remains challenging. In this study, a high-hardness particle-toughened, self-stratifying organic layer with high photothermal conversion rate was developed to enhance coating durability and ice-repellent performance. By optimizing the ratio of dopamine (DA) and sodium alginate (SA), a hydrophobic photothermal agent (DPSn) with high hardness and a significant light-heat effect was synthesized. A durable, hydrophobic photothermal anti-ice coating (AR/20 %PDMS/x%DPS1) with varying DPS1 amounts was successfully created using a straightforward one-step spray method, utilizing the self-stratification characteristics of acrylic resin (AR) and polydimethylsiloxane (PDMS), along with the toughening effect of DPSn. The fiber cross-linked structure of DPS1 achieved a photothermal conversion rate of 87.5 %. Adding 4 wt% DPS1 increased the surface temperature of the AR/20 %PDMS coating to 96.5 ± 2.4 °C and boosted the coating’s adhesion strength from 6.70 ± 0.3 MPa to 7.23 ± 0.7 MPa. The AR/20 %PDMS/4%DPS1 coating demonstrated excellent anti-/de-icing performance after 60 friction cycles, 60 icing/de-icing cycles, and 132 h of acid-base immersion. Its simple preparation process and durable ice-repellent properties make it highly suitable for practical applications in photothermal hydrophobic soft coatings.

A reinvestigation on combined dry and wet adhesive contact considering surface tension

The present study theoretically explores combined dry and wet adhesive contact between a rigid sphere and elastic semi-half substrate, in which dry contact is encircled by liquid bridge. We consider threefold effects of liquid bridge on contact behavior, namely Laplace pressure induced by the curved surface of liquid meniscus, surface tension at the triple-phase junction and alternation of adhesion energy between solid surfaces ascribed to liquid immersion. A clear novelty in this study is the investigation on the effect of surface tension at the vapor-liquid-solid junction on the adhesive contact response, in contrast to previous studies. The model solution predicts that the contact behavior and adhesive strength are strongly dependent on surface wettability (manifested by contact angle), liquid volume and the contact system's rapidity in achieving thermodynamic equilibrium. It is found that the transition of the pull-off force is evidently different from Maugis-Dugdale model in terms of a couple of interesting characteristics. Moreover, it is unveiled that the jump instabilities and hysteresis of force-separation curves are highly affected by surface wettability and liquid volume. These theoretical results can not only shed lights on the mechanism of liquid-mediated adhesion employed by animals and plants, but also provide us inspiration for development of biomimetic adhesive devices.

Aqueous Electrophoretic Deposition of Yttrium-Doped Nanobioactive Glass/Collagen/Chitosan Orthopedic Coatings on 316L SS

The current study used yttrium-doped nano bioactive glass (Y-nBG, based on 62 SiO2 – (33 – x) CaO – 5 P2O5 – x Y2O3 mole %), collagen and chitosan composites for coating stainless steel 316L by an electrophoretic deposition (ED) method. x = 0, 1 and 3 moles % and the corresponding samples encoded as SS/Col-Chit, SS/BG-Y0/Col-Chit and SS/BG-Y3/Col-Chit, respectively. TGA, FTIR, SEM-EDX, contact angle, adhesion strength and in vitro bioactivity in SBF. Following SBF immersion, FTIR and SEM-EDX investigations were carried out. Furthermore, the coatings were loaded with gentamicin drug, the drug-releasing profile and mechanism of release were evaluated. Coatings' antibacterial efficacy was also assessed. The results showed formation of homogeneous coatings with good adhesion strengths, 1.39 MPa, 0.55 MPa and 0.81 MPa and enhanced the wettability by decreasing the contact angle 36.4, 21.8 and 11.7for SS/BG-Y0/Col-Chit and SS/BG-Y3/Col-Chit coatings, respectively. Also, in vitro bioactivity of coatings containing nBG was demonstrated by promoted apatite formation after immersion in SBF through the presence of calcium and phosphorus in SEM-EDX analysis. Furthermore, the antibiotic gentamicin was showed sustained release profile over time by diffusion mechanisms based on the Higuchi, Fickian and Weibull models. As well, all coatings containing drugs have an antibacterial effect. Overall, these findings suggest that the prepared coatings have potential for orthopedic applications.

Activation of muscle amine functional groups using eutectic mixture to enhance tissue adhesiveness of injectable, conductive and therapeutic granular hydrogel for diabetic ulcer regeneration

Herein, Polydopamine-modified microgels and microgels incorporated with superficial epoxy groups were synthesized and applied as precursors for the fabrication of four granular hydrogels. To enhance the tissue adhesiveness, a ternary deep eutectic solvent was synthesized to activate the muscle amine functional groups facilitating the formation of robust NC bonds at ambient conditions. At a certain shear rate of 10 s−1, hydrogel DMG displayed a viscosity of 9×103 Pa/s, representing the highest complex viscosity among the tested hydrogels primarily driven by quinone groups in PDA which enhanced reversible interactions, thereby increasing particle cohesion. Moreover, the intersection point escalating from about 4×103 to approximately 9×104 as the concentration of DMG increased from 0 % (for MG) to 70% (7D3MG) by weight. There was a decrease in adhesion strength from 0.45 ± 0.08 N in MG to 0.39 ± 0.16 N, 0.35± 0.18 N, and 0.33 ± 0.15 N for 3D7MG, 7D3MG, and DMG respectively, suggesting that MG was capable of forming numerous covalent bonds, thereby enhancing its adhesion to the substrate. The type of eutectic mixture affected the electrical conductivity and a very important point was the changes in resistance value with time. For MG catalyzed by [DES]AZG, the resistance increased only by 1.3 % (from 3.37 to 3.81 kΩ) at day 3 and 37.09 % (from 3.37 to 4.62 kΩ) at day 5. The 3D7MG hydrogel exhibited superior therapeutic efficacy toward diabetic wound regeneration. The proliferation index value for 3D7MG-[DES]AZG and 3D7MG-[DES]AG were calculated 42.3 % and 58.6 %, respectively, while the control group exhibited a lower value of 37.8 %.

Transparent and smooth liquid-repellent coating for self-cleaning applications of solar cells

Abstract Solar energy as a clean, renewable energy source is perceived as a potential remedy to the environmental and climate degradation caused by fossil fuels. However, the surface contamination severely diminishes the photovoltaic conversion efficiency of solar cells. Liquid-repellent coatings that combine transparency and durability could be candidates for self-cleaning application of solar cells. Herein, a smooth liquid-repellent coating (SLRC) was developed by synergizing organosilicon and fluorine and was cured at room temperature. Owing to the low-surface-energy groups and flexible chains enriched on the SLRC surface, as well as cross-linking reactions and functional additives within the SLRC matrix, it exhibited liquid-repellency and UV-shielding properties. Moreover, SLRC could be applied to solar cells by spraying methods and displayed efficient self-cleaning properties. Finally, the adhesion strength and durability of SLRC were also verified, confirming that it had great potential for application in solar cells, opening the avenue for the development of self-cleaning coatings.

Comparative characteristics of the adhesive strength of self-etching adhesives

Comparative characteristics of the adhesive strength of self-etching adhesives

Bonding strength of universal adhesives to laser-etched deep/superficial dentin

Bonding strength of universal adhesives to laser-etched deep/superficial dentin

Influence of doping elements X (X= Hf, Zr, Y, Re, Pd, Ir) on the structural stability and tension property of α-Al2O3/PtAl2-S interfaces

Pt-Al coatings are promising materials for protective materials for turbine blades in new-generation aero-engines. Therefore, it is worth noting that the interface stability and tension property between Pt-Al and the oxide layer, prolonging coating service time. However, systematic studies of doping elements effects on interface adhesion of α-Al2O3/PtAl2 with and without impurity S are still lacking. In this paper, the site preference of the six elements (Hf, Zr, Y, Re, Pd, and Ir) in the PtAl2 alloy, effects of doping elements on the interface adhesion and tension properties of the α-Al2O3/PtAl2-S interface are further explored, performing the first-principles calculation method. Considering comprehensively, Y doping has an excellent enhancement effect on the static interface adhesion and dynamic tensile strength, regardless of whether impurity element S exists in the α-Al2O3/PtAl2 interface. This study will provide necessary theoretical guidance for the composition design of Pt-Al coating and the research of new metal protective coating materials.

Finite element modeling for cohesive/adhesive failure of adhesive structures with a thermosetting resin

In this study, we established a novel method based on the finite element method (FEM) for predicting the strength of adhesive structures. Viscoplasticity, void growth, and cohesive zone model were introduced into the FEM to create a nonlinear damage growth (NDG) model. This model was used to comprehensively analyze the process zones within the adhesive layer. Furthermore, the embedded process zone approach was used to develop an interface constitutive law that averages the mechanical response of the adhesive layer. This modified Ma–Kishimoto (MMK) model can accurately represent the adhesive layer as an interface element and is computationally efficient. Furthermore, the study obtained the necessary interface properties for the MMK model from the NDG model, creating a numerical material test that can approximate the effect of the process zone. To validate the proposed method, single-lap shear tests were performed, and the accuracy of the predicted strength and deformation field was evaluated. The damage evolution in the NDG model and the MMK model were compared, and the scope of application of the MMK model was discussed. The results of this study can be used as a reference for the failure mechanism of thermosetting adhesives and establishment of design indices for adhesive structural strength.

Self-Growing Hydrogel Bioadhesives for Chronic Wound Management.

Hydrogel bioadhesives have emerged as a promising alternative to wound dressings for chronic wound management. However, many existing bioadhesives do not meet the functional requirements for efficient wound management through dynamically mechanical modulation, due to the reduced wound contractibility, frequent wound recurrence, incapability to actively adapt to external microenvironment variation, especially for those gradually-expanded chronic wounds. Here, a self-growing hydrogel bioadhesive (sGHB) patch that exhibits instant adhesion to biological tissues but also a gradual increase in mechanical strength and interfacial adhesive strength within a 120-h application is presented. The gradually increased mechanics of the sGHB patch could effectively mitigate the stress concentration at the wound edge, and also resist the wound expansion at various stages, thus mechanically contracting the chronic wounds in a programmable manner. The self-growing hydrogel patch demonstrated enhanced wound healing efficacy in a mouse diabetic wound model, by regulating the inflammatory response, promoting the faster re-epithelialization and angiogenesis through mechanical modulation. Such kind of self-growing hydrogel bioadhesives have potential clinical utility for a variety of wound management where dynamic mechanical modulation is indispensable.

Thermally-responsive dismantlable adhesion system for steel plates using methacrylate copolymers containing a tert-butoxycarbonyl group

A drastic change in the bulk properties of adhesive materials as well as a reduction of interfacial interaction is an important key for the development of dismantlable adhesion systems, i.e., reliable bonding systems with a function of on-demand debonding. The deprotection of tert-butoxycarbonyloxy (BOC) groups included in adhesive polymers can be applied to the construction of a dismantlable adhesion system for steel plates combined with acrylic and epoxy adhesives. In this study, we evaluated the adhesive properties of the copolymers of 2-(tert-butoxycarbonyloxy)ethyl methacrylate (BHEMA), glycidyl methacrylate (GMA), and 3-trimethoxysilylpropyl methacrylate (SMA) for the dismantlable bonding of steel plate cold commercial (SPCC). Spontaneous dismantling of the SPCC adhesive structures was achieved after heat treatment under the conditions at 210 °C for 15 min when the BHEMA/GMA/SMA copolymers with an appropriate copolymer composition were used as the acrylic adhesives or the primers for epoxy adhesion. We discuss the interfacial interactions between the adherend and the adhesives for reliable adhesion and the effects of the deprotection of the BOC groups for dismantling to exhibit both an adhesion strength required for metal bonding and a rapid decrease in the strength by thermal stimulus.

Phosphorus/boron-containing, flame-retardant polyurethane elastomers with great mechanical, shape-memory, and recycling performances

Based on sustainable development strategy and practical application requirement, it is crucial to develop high-strength, recyclable, and flame-retardant polyurethane (PU) elastomers. Hence, a flame-retardant, reprocessable, high-performance polyurethane elastomer (PU-DP 1–7) with dynamic boronic ester bonds and phosphorus-containing groups was well-designed and prepared. The chemical structure of PU-DP 1–7 was confirmed by Fourier transform infrared spectrometry (FTIR) and X-ray photoelectron spectroscopy (XPS). PU-DP 1–7 shows a transmittance of about 60 % at the wavelength of 900 nm, and phosphorus and boron elements are evenly distributed within its surface, confirming the formation of uniform cross-linking network. The inclusion of phosphorus-and boron-containing groups endows PU-DP 1–7 with a vertical combustion (UL-94) V-0 rating, indicative of desired flame retardancy. In addition, PU-DP 1–7 exhibits a tensile strength of 42.7 MPa and an elongation at break of 616.9 %, with high adhesion strengths towards various substrates due to abundant hydrogen bonds within its network. Furthermore, the dynamic borate ester bonds endow PU-DP 1–7 with superior physical recycling and shape-memory properties. After hot-pressing at 130 °C, the reformed PU-DP 1–7 film shows an 83.6 % recovery efficiency in terms of elongation at break. This work presents an integrated strategy to create flame-retardant, recyclable polyurethane elastomers with great mechanical and shape-memory performances by introducing phosphorus-containing segments and dynamic boronic ester bonds.

WITHDRAWN: Characterization of Ag2O nanorods/TiO2 nanotubes hybrid coating for potential orthopedic implant applications

In this study, the potential of nanorod/nanotube hybrid arrays for orthopedic coatings was explored. The Ag2O nanorods/TiO2 nanotubes (ANRs/TNTs) hybrid coating was synthesized on Ti6Al7Nb using a multi-step procedure involving primary anodization, annealing, and secondary anodization processes. The process began with primary anodization, fostering the growth of TNTs, succeeded by thermal treatment for crystallization, and deposition of an Ag layer using physical vapor deposition (PVD) magnetron sputtering. Subsequently, secondary anodization was conducted on Ti6Al7Nb, which was initially coated with Ag-deposited TNTs, culminating in the formation of a hybrid coating. In the hybrid coating, the mean inner diameter of the TNTs was measured at 32.2 ± 8.0 nm, while the average inner diameter of the ANRs stood at 59.0 ± 30.6 nm. The hybrid coating exhibited notably higher hardness values (75.8 ± 3.2 HV) compared to both anodic TNTs (HV 45.5 ± 1.0) and crystallized TNTs (HV 54.0 ± 1.6), while its adhesion strength reached 871.5 ± 3.86 MPa, highlighting robust bonding with Ti6Al7Nb. In vitro bioactivity results confirmed bone-like apatite layer formation on ANRs/TNTs hybrid coating after 14 days in simulated body fluid (SBF), indicating enhanced bioactivity. These findings open promising avenues for advanced orthopedic coatings, with potential applications in facilitating osseointegration, drug delivery, and localized treatments in future biomedical applications.

Microstructure evolution and degradation process of AlCrTiSiN coatings with different Si contents at high temperatures

The microstructure evolution of AlCrTiN and AlCrTiSiN coatings containing 4, 6.8, and 10.6 at.% Si was studied at temperatures ranging from 800 to 1100 °C. The AlCrTiN coating exhibits a single-phase fcc-(Al,Cr,Ti)N structure, while the AlCrTiSiN coatings transition from a nanocomposite structure, composed of fcc-(Al,Cr,Ti)N and amorphous a-SixNy, to a fully amorphous structure as the Si content increases. The hardness and adhesion strength of coatings initially rise, peaking at 24 GPa and 44 N respectively, due to the formation of the nanocomposite structure. However, these properties decline as the coatings become fully amorphous. At elevated temperatures, severe oxidation leads to the gradual formation of layered oxides. Concurrently, phase transformation, spinodal decomposition, and crystallization occur within the nitride layer. The addition of Si enhances oxidation resistance by promoting the rapid formation of a dense and protective oxide layer, and by reducing nitrogen release and TiO2 formation. However, at 1000 and 1100 °C, the coating with 10 at.% Si exhibits slightly faster oxidation compared to the 6.8 at.% Si coating, as the increased Si content reduces the Al content, limiting the coating's ability to regenerate the protective oxide layer.

Effect of drying temperature on binder/current collector interfacial adhesion in electrode manufacturing of Li-ion batteries

Li-ion battery manufacturing process parameters are critical to the electrode properties and the final cell electrochemical performance. During the electrode drying process, the drying temperature plays a critical role on the binder migration, which affects the interfacial adhesion between the electrode and the current collector. However, the influence of the temperature on the properties of the binder material and the binder/current collector interface is yet unknown. In this work, we studied the effect of drying temperature on the interfacial adhesion between the binder and the current collector by direct coating of polyvinylidene fluoride (PVDF) solution on Al foil and then drying at various temperatures. The interfacial adhesion strength between the PVDF and the Al foil was significantly increased, from 9.72 N/m (dried at room temperature) to > 665.80 N/m (dried at 200 ℃) with increased temperature. DSC and XRD analyses showed the changes in the crystalline forms of PVDF under different drying temperature. This work revealed that the drying temperature during electrode manufacturing should be considered from the aspects of both binder migration in mid-stage and PVDF crystalline properties in late-stage solvent drying.

High-strength self-healing multi-functional hydrogels with worm-like surface through hydrothermal-freeze-thaw method

Soft self-healing materials are promising candidates for flexible electronic devices due to their exceptional compatibility, extensibility, and self-restorability. Generally, these materials suffer from low tensile strength and susceptibility to fracture because of the restricted microstructure design. Herein, we propose a hydrothermal-freeze-thaw method to construct high-strength self-healing hydrogels with even interconnected networks and distinctive wrinkled surfaces. The integration of the wrinkled outer surface with the three-dimensional internal network confers the self-healing hydrogel with enhanced mechanical strength. This hydrogel achieves a tensile strength of 223 kPa, a breaking elongation of 442%, an adhesion strength of 57.6 kPa, and an adhesion energy of 237.2 J m-2. Meanwhile, the hydrogel demonstrates impressive self-repair capability (repair efficiency: 93%). Moreover, the density functional theory (DFT) calculations are used to substantiate the stable existence of hydrogen bonding between the PPPBG hydrogel and water molecules which ensures the durability of the PPPBG hydrogel for long-term application. The measurements demonstrate that this multifunctional hydrogel possesses the requisite sensitivity and durability to serve as a strain sensor, which monitors a spectrum of motion signals including subtle vocalizations, pronounced facial expressions, and limb articulations. This work presents a viable strategy for healthcare monitoring, soft robotics, and interactive electronic skins.

High mechanical, self-adhesive oxidized guar gum/chitosan hydrogel prepared at room temperature based on a nickel-urushiol catalytic system for wireless wearable sensors

Recently, sensors constructed on the basis of hydrogel are playing a major role in health detection such as motion detection and breathing monitoring. However, the common hydrogels have poor mechanical properties, insufficient adhesion and complex preparation processes, which hinder the further use of such sensors. In this paper, the conductive hydrogel (P(AA-UH)-OGG-CS/NiCl2) composed of acrylic acid (AA), oxidized guar gum (OGG) and chitosan (CS) was prepared at room temperature through the dynamic redox reaction of nickel chloride (NiCl2) and urushiol (UH). In detail, the reduction group (phenolic hydroxyl) of UH and Ni2+/Ni3+ pair form a semi-quinone/quinone redox dynamic cycle system, allowing the hydrogel to quickly gel at room temperature for 3 min. The catechol group in UH also promotes the hydrogel to have a superior adhesion strength of 25.23 kPa to pig skin and a strong repeated adhesion performance. In addition, the dynamic Schiff base bond created by the interaction of OGG and CS elevated the tensile stress of the hydrogel to 67.54 kPa. After the hydrogel is assembled into the sensor, it has high sensitivity and high stability to different strains, and has great application prospects in the field of actual human health monitoring.

Microstructure, mechanical and tribological characterization of magnetron sputtering ZrN and ZrAlN coatings

In this research paper, mechanical and tribological characterization of novel high wear-resistant ZrN-ZrAlN coatings are presented. The varying concentrations of AlN is chosen to evaluate the influence of AlN the surface morphological, nanomechanical, and tribological properties of the composite coating. The coatings were developed on D9 steel substrates using nitrogen reactive gas radio frequency (RF) magnetron sputtering of zirconium and aluminium targets in an argon plasma. Variable power density for the aluminium target and constant power density for zirconium, was used to obtain in a systematic way, the variable concentration of AlN in the coating. Surface morphological studies were carried out to evaluate composition and crystal structure using X-ray diffraction (GIXRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Coatings display a polycrystalline structure, but the level of crystallinity decreases with higher AlN concentration. Nanomechanical and nano scratch testing, along with tribological experimental studies were performed to comprehensively analyse performance of the developed coatings. Higher hardness of composite coating is achieved with optimal concentration of AlN in ZrN-ZrAlN coating. Adhesion strength of the coatings increased with the increase in the concentration of AlN. ZrN-ZrAlN coatings depicted low wear, however coatings containing AlN exhibits superior wear resistance.