Interfacial Adhesion Strength Research Articles

Graphene-reinforced epoxy powder coating to achieve high performance wear and corrosion resistance

The corrosion and wear resistance of organic coatings are the key factors to maintain their good function. Graphene-based polymer composites have attracted incredible attention owing to their superior physicochemical properties than polymers. In this study, the effect of graphene nanosheet (G) additives on the microstructure, adhesion behaviors, anti-wear performance and corrosion resistant of epoxy powder coatings (EP) were systematically investigated. Field emission scanning electron microscope (FESEM) results verified that the mild addition of G could enhance the compactness of EP and reduced microstructure defects such as cracks, cavities, and voids. The adhesion and tribological results confirmed that the graphene-contained epoxy powder composite coatings (G/EP) could demonstrate significant improvement compared to the EP, which potentially attributed to the high mechanical and self-lubrication properties of G nanoflakes. In particular, the electrochemical and salt spray evaluation revealed that the enhanced physical barrier protection performance and outstanding anti-corrosion capacity of the G/EP composite coating containing 0.4 wt% G. The current study provides a promising metal protection strategy for the development of graphene-enhanced organic powder coatings applied in mechanical-corrosion coupling environments. This article reveals for the first time that graphene nanosheets enhance the interfacial adhesion strength of organic powder coatings, as well as the effect on wear and electrochemical performance.

Polyphenylene sulfide-modified carbon fiber reinforced high-strength composites via electrophoretic deposition

The performance of carbon fiber (CF)–reinforced thermoplastic composites is influenced by the interfacial adhesion strength of the fiber and thermoplastic matrix. In this study, the electrophoretic coating of silane-grafted polyphenylene sulfide (PPS) particles on the CF surface was used to quantitatively control the interfacial adhesion between the CF and PPS matrix. The mechanism of the modification method was discussed, and the interfacial shear strength of the CF/PPS composites was numerically and experimentally investigated and found to be significantly higher (65.8 ± 4.76 MPa) than that of conventional thermoplastic systems. Scanning electron and atomic force microscopies of the fractured surfaces confirmed that the predominant failure mechanisms involved the deformation and breakage of the matrix due to the strong interphase in the interfacial region. A straightforward and controllable electrophoretic coating process was shown to be effective at improving the interfacial strength and mechanical properties of CF/PPS composites.

Studies on the Mechanical Models and Behaviors for the Stamp/Film Interface in Microtransfer Printing

The adhesion/delamination characteristics at the stamp/film interface are critical for the efficiency of film microtransfer printing technology. To predict and regulate the interface mechanical behaviors, finite element models based on the J-integral, Virtual Crack Closure Technology (VCCT), and the cohesive zone method (CZM) were established and compared. Then, the effects of pulling speed and interface parameters on the pull-off force, which is used to characterize the interface adhesion strength, were investigated. Comparisons between the simulation results and previous experimental results demonstrated that the model based on the CZM was more applicable than the models based on the J-integral and VCCT in analyzing the adhesion/delamination behaviors of the stamp/film interface. Furthermore, the increase in pulling speed could enlarge the pull-off force for the viscoelastic stamp/film interface, while it had no influence on the pull-off force for the elastic stamp/film interface. In addition, a larger normal strength and normal fracture energy resulted in a larger pull-off force, which was beneficial to the realization of the picking-up process in microtransfer printing.

Robust and dynamic underwater adhesives enabled by catechol-functionalized poly(disulfides) network.

Developing molecular approaches to the creation of robust and water-resistant adhesive materials promotes a fundamental understanding of interfacial adhesion mechanisms as well as future applications of biomedical adhesive materials. Here, we present a simple and robust strategy that combines natural thioctic acid and mussel-inspired iron-catechol complexes to enable ultra-strong adhesive materials that can be used underwater and simultaneously exhibit unprecedentedly high adhesion strength on diverse surfaces. Our experimental results show that the robust crosslinking interaction of the iron-catechol complexes, as well as high-density hydrogen bonding, are responsible for the ultra-high interfacial adhesion strength. The embedding effect of the hydrophobic solvent-free network of poly(disulfides) further enhances the water-resistance. The dynamic covalent poly(disulfides) network also makes the resulting materials reconfigurable, thus enabling reusability via repeated heating and cooling. This molecule-engineering strategy offers a general and versatile solution to the design and construction of dynamic supramolecular adhesive materials.

Designing BN@CF hybrid to enhance the epoxy resin towards outstanding anti-corrosion and anti-wear performances

Carbon fiber-reinforced composites (CCs) have been widely used in many advanced applications due to their high specific strength, good corrosion resistance, and wear resistance. Despite recent progresses, obtaining high-performance and durable CCs remains difficult because of low fiber/matrix interfacial adhesion. Here, we designed and fabricated hexagonal boron nitride modified carbon fiber (BN@CF) by chemically grafting functional hexagonal boron nitride (F-BN) nanosheets on polydopamine modified carbon fiber (PDA-CF) surface and used it in increasing the strength of interfacial adhesion between the fibers and epoxy resin (EP). Tensile strength and interfacial shear strength (IFSS) of EP/BN@CF composite increased by 13.8% and 87.2%, respectively, compared with those of pure EP. BN@CF hybrid with unique structure endowed the epoxy composite coating with excellent corrosion resistance property, which greatly enhanced the impedance by two orders of magnitude relative to those of other coatings. Comparing with pure EP, EP/BN@CF composite had a 37.8% reduction in coefficient of friction and 83.0% reduction in wear rate. Such distinguished anti-corrosion performance and wear-resistance were ascribed to the increased fiber/matrix interfacial adhesion strength of EP/BN@CF composite. We believe that the fabricated BN@CF hybrid will open up avenues for various applications.

Enhanced Interfacial Adhesion of Nylon 66 to Epoxy Resin EPON 825 by Non-thermal Atmospheric Pressure Dielectric Barrier Discharge Plasmas

Poly(hexamethylene adipamide), nylon 66, is a popular plastic that requires high surface wettability and strong adhesive bonds for many applications. However, pristine nylon is difficult to bond due to its hydrophobic nature and poor surface wettability. The objective of this work was to modify the physio-chemical surface properties of nylon 66 via a novel atmospheric plasma surface treatment approach using oxygen (O2) or water vapor (H2O) plasma glow. The surface hydrophilicity of the plasma-treated nylon surface was substantially enhanced immediately after either helium (He)/H2O or He/O2 plasma surface treatment. The average water contact angle was reduced from 65 degrees to ~30 degrees after He/H2O plasma and ~40 degrees after He/O2 plasma treatments. The improved hydrophilicity was also evidenced by the increased intensities of the surface oxygen and hydroxyl bonds in the X-ray photoelectron spectra. The interfacial adhesion strength of nylon surfaces before and after plasma treatment was further evaluated by uniaxial tensile tests of nylon single-joint lap shears bonded with three adhesives, i.e., thermoset epoxy resins EPON 825/ JEFFAMINE D-230 and EPON825/JEFFAMINE D-2000, and the thermoelastic polyurethane adhesive Sikaflex 252. The most significant improvements in bond strengths due to plasma treatment were found for lap shears bonded with the EPON 825/JEFFAMINE D-230 epoxy resin; their shear strengths with maximum loads were more than doubled—from 299–451 to 693–1594 N—after plasma treatment and were further enhanced by a factor of four to 895–1857 N after a subsequent silane treatment. In contrast, the bond strength of lap shears bonded with EPON 825/JEFFAMINE D-2000 and Sikaflex was not significantly improved because of the different a, re-affirming the importance of adhesive bulk properties This work presents the preliminary success of effective surface functionalization leading to enhanced interfacial adhesive bonds for nylon 66 via the development of scalable atmospheric plasma surface treatments.

Comparative tribological performance and erosion resistance of epoxy resin composite coatings reinforced with aramid fiber and carbon fiber

In this work, chitosan modified aramid fiber (MAF) and carbon fiber (MCF) were prepared by simple self-assembly of chitosan on the fibers. The interface adhesion strength between fiber and epoxy resin was greatly improved, due to the active groups on the surface of chitosan. Compared with pristine composites, MAF/EP and MCF/EP showed impressive improvements of 15.61% and 18.06% in interfacial stress strength (IFSS), respectively. The effects of MAF and MCF on the tribological performance and erosion resistance of composite coatings were comprehensively studied. Compared with MAF/EP, the tensile strength of MCF/EP composite coating increased 11.09%. The test results showed that the MCF reinforced epoxy composite coating performed better anti-wear ability than that of MAF, which was due to the load-capacity and strength of MCF/EP was higher. Compared with MAF/EP, the wear rate of MCF/EP composite coating was reduced by 66.35%. Furthermore, the load-capacity and interface stress strength of MCF was higher than that of MAF, lead the erosion properties of MCF/EP was much better than MAF/EP. Compared with MAF/EP resin, the erosion volume of MCF/EP composite coating was reduced by 50.38%, showing outstanding erosion resistance, which was attributed to the resistance of high-strength carbon fiber to SiC particles.

Atomic mechanisms of separation failure at the asphalt–aggregate interface and its dependence on aging and rejuvenation: Insights from molecular dynamics simulations and DFT calculations

The microscopic interfacial properties between asphalt and aggregates determine the macroscopic cracking behaviors of asphalt mixtures. To provide guidance on durability enhancement for reclaimed asphalt pavement mixtures that are prone to cracking, the fracture resistance of asphalt–aggregate interface and its dependence on aging and rejuvenation was investigated by molecular dynamics simulations and density functional theory. The results revealed that although the separation resistance is influenced by the loading rate, temperature and aggregate composition, the separation of the virgin interface system usually occurs within the asphalt region. The aged interface also tends to separate inside the asphalt, but if the asphalt is severely aged, debonding occurs at the asphalt–aggregate interface because the cohesive strength within asphalt is stronger than the interfacial adhesion strength. The aged interface exhibits higher resistance to complete fracture than virgin interface under non-repetitive loading. However, the enhanced molecular polarity of aged asphalt reduces its molecular flowability, thus weakening the resistance of aged interface to fatigue failure. Rejuvenators containing both polar carboxyl groups and nonpolar alkyl groups function as intermediaries to promote the compatibility of aged asphalt molecules with virgin molecules, thus restoring the flowability and fatigue failure resistance of aged interface systems.

Correction: Boruah, D.; Zhang, X. Effect of Post-Deposition Solution Treatment and Ageing on Improving Interfacial Adhesion Strength of Cold Sprayed Ti6Al4V Coatings. Metals 2021, 11, 2038

The authors wish to make the following corrections to this paper [...]

Interfacial structure and properties of isotactic polybutene-1/polyethylene blends

Abstract Polymer blending is one of the most economical and effective techniques for achieving products with high comprehensive performances. However, the immiscibility between polymers results in a weak interface, which is typically the position where material failure starts when an external force is applied. Therefore, understanding and controlling the interfacial structure are important for controlling the failure behavior of polymer blends and achieving advanced materials. In this study, the related work was performed on a crystal/crystal blend of isotactic polybutene-1 and polyethylene (iPB-1/PE). The results indicated that iPB-1 and PE were partially miscible in a wide temperature window (140–220°C), and the phase separation of iPB-1/PE blends was retarded at 180°C, resulting in an increase in the interfacial thickness and interfacial adhesive strength when iPB-1/PE crystallized at a low temperature. In addition, the iPB-1/high-density PE (HDPE) samples exhibited higher interfacial adhesive strength than the iPB-1/linear low-density PE, which was attributed to the relative streamline chain structure and the wide molecular weight distribution of HDPE and improved the interpenetration, crystallization, and miscibility of iPB-1 and HDPE at the interface. During storage at room temperature, the interfacial adhesive strength of iPB-1/PE decreased because of the spontaneous crystal transition of iPB-1.

Performance of clay–epoxy interface at different points on proctor curve

Different coating materials are applied at the soil-structure interface to enhance the interfacial performance between soil and the structure. The primary objective of this work was to investigate the mechanism behind the interfacial adhesive strength between epoxy coating and soil. Soil can exhibit different pore microstructures upon variation in its moisture content. This can potentially affect the soil-polymer coating interface performance. Compacted soils at different water contents on the proctor curve were considered and its porosity was estimated applying Mercury Intrusion Porosimetry (MIP). Load-displacement responses from macro-mechanical tests showed a highest interfacial strength not at the optimum moinsture content, however,at the dry of optimum. Results had indicated that the major contributions to the interfacial strengths arises from the plastic deformation of epoxy which penetrates through clay surface pores. In addition, the physical work of adhesion at the interface arising from the electron donor oxygen sites at the clay siloxane surface and epoxy functional groups were considered to affect the initial pre-peak stage of the load-displacement characteristics.

IMPROVED ADHESION IN ELASTOMERIC LAMINATES USING ELASTOMER BLENDS

ABSTRACT Interlayer adhesion between distinct rubber compositions in elastomeric laminates has been pursued by a variety of approaches, including treating surfaces, introducing assistant chemicals, and interposing a “transition layer.” Each approach, however, may be specific to the elastomer chemistries and may not be easily transferred to other rubber composition pairs in laminates. These limitations were overcome by inserting a layer at the interface that is a blend of each of the elastomer compositions of the adjacent layers and that increases the interfacial adhesion strength of the resultant laminates. This approach was demonstrated using three elastomer systems: fluoroelastomer (FKM), acrylonitrile–butadiene rubber (NBR), and isobutylene–isoprene rubber (IIR). The adhesion in the three-layer laminate (FKM/NBR/IIR) was improved with the addition of an FKM-NBR blend layer between the FKM and NBR layers and the addition of an NBR-IIR blend layer between the NBR and IIR layers. The five-layer laminate (FKM/[FKM-NBR blend]/NBR/[NBR-IIR blend]/IIR) was also fabricated. Interfacial adhesion was evaluated using the T-peel test according to ASTM D1876, which showed that the blends provided improved adhesion. Scanning electron microscope images were used to study the interface region. The proposed idea offers a general approach to improve interfacial strength that is widely applicable to other multilayer elastomer laminates.

Tailoring Interfacial Adhesion between PBAT Matrix and PTFE-Modified Microcrystalline Cellulose Additive for Advanced Composites.

Cellulose materials have the potential to serve as sustainable reinforcement in polymer composites, but they suffer from challenges in improving interfacial compatibility with polymers through surface modification. Here, we propose adjusting the interfacial compatibility between microcrystalline cellulose (MCC) and poly (butylene adipate-co-terephthalate) (PBAT) through the strategy based on surface energy regulation. Mechanical ball milling with polytetrafluoroethylene (PTFE) powder was used to simultaneously pulverize, and surface modify MCC to produce MCC sheets with different surface energy. The modified MCC was used to reinforce PBAT composites by simple melt blending. The surface morphology, surface energy of MCC, and the amount of friction transferred PTFE during ball milling were characterized. The mechanical performance, composite morphology, crystallization behavior and dynamic thermomechanical analysis of the composites were investigated. The interfacial adhesion strength of composites closely relates to the surface energy of modified MCC. When the surface energy of MCC is closer to that of the PBAT matrix, it exhibits the better interfacial adhesion strength, resulting in the increased mechanical properties, crystallization temperature, storage modulus, and loss modulus. This work provides effective strategy for how to design fillers to obtain high-performance composites.

Covalent treatment of carbon fibre with functionalized MoS2 nanosheets using thiol-ene click chemistry: The improvement of interface in multiscale epoxy composites

The multiscaling method is contemplated as an effective approach for improving the interfacial adhesion in carbon fibre composites. Nonetheless, the lack of interactions between the nanomaterials and the other constitutes including fibre and matrix resulted in the deterioration of mechanical performance in composites. Herein, the combination of a scalable synthesis method based on ball milling and thiol-ene click chemistry has been utilized to graft the functionalized MoS 2 nanosheets with large lateral dimensions (∼537 nm) on the carbon fibres surface for the first time. The proposed method did not significantly affect the mechanical properties of the carbon fibre, leading to augmentation in the performance of composites by the virtue of higher surface energy and roughness of the fibre surface. In other words, the obtained results have demonstrated that the presence of activated MoS 2 nanosheets on the carbon fibre surface possesses the ability to promote interfacial adhesion and interlaminar shear strength by 74% and 36% respectively, compared to the pristine unsized carbon fibre. Additionally, the effectiveness and the efficacy of MoS 2 -CF reinforcements can be delineated by the enhancements of flexural strength and modulus of multiscale composites by 49.5% and 33.6%, respectively. The morphology of both fibres and fractured surfaces of composites indicated that the random distribution of nanosheets on the fibre surface facilitates the energy dissipation via breakage, pullout, and bridging mechanisms which subsequently improved the overall performance of the developed composites.

Controlling PA6/PET adhesion to facilitate interfacial fracture

Microfibers get often produced in the form of bicomponent polymer systems. The materials of choice are Nylon 6 (PA6) and poly(ethylene terephthalate) (PET). This combination of PA6 and PET is preferable because of its beneficial attributes (i.e., thermal stability, mechanical strength, etc.). PA6 and PET exhibit high adhesion when processed at elevated temperatures due to chemical bonds formation by aminolysis of the ester group in PET with a secondary amine in PA6. These fibers are split/fibrillated by mechanical energy (hydroentangling or needle punching). For energy input, it is desirable to have adhesion between the PA6 and PET materials that is not too strong to allow for easy polymer splitting. Therefore, we developed a method for tailoring the PA6/PET interface adhesion by adding modifiers that react preferentially with the PA6 component. The reactivity between PA6 and PET was investigated by spin coating thin films of PA6 and PET on silicon wafers and annealing them at high temperatures. The reaction between PET and small molecules containing secondary amines (i.e., caprolactam, diallyamine, diethylamine, and diisopropylamine) shows a chemical bond between the ester group in PET and the secondary amine group. The poly(styrene-alt-maleic anhydride) (PSMA) and poly(octadecene-alt-maleic anhydride) (POMA) were chosen as model polymer interfacial modifiers. The feasibility of modifying secondary amines is examined by reacting the two modifiers, PSMA and POMA, with small molecules containing secondary amine groups. PA6 and PET display high fracture toughness (i.e., adhesion strength) at elevated temperatures and longer annealing times because of strong interactions between the amine and ester groups in PA6 and PET, respectively. We then assess the adhesion strength between PA6 and PET modified with PSMA and POMA. Both modifiers reduce interfacial adhesion strength between PA6 and PET. Therefore, it is feasible to tailor adhesion at the PA6/PET interface, which could prove helpful in microfibers production.

Research progress on surface modification and application status of UHMWPE fiber

Abstract Ultrahigh molecular weight polyethylene (UHMWPE) fiber is a high-performance material with superior properties of high strength and modulus, low density, wear resistance and corrosion resistance. But the development of UHMWPE fiber reinforced polymers is hindered due to its inert inactive surface and poor interfacial adhesion with polymer matrix. This work presents the research progress on surface modification techniques, including ‘dry’ treatment, strong oxidant treatment, chemical grafting and coating, of UHMWPE fiber and the mechanisms of the improvement on surface properties and interfacial adhesion strength between the UHMWPE fiber and the polymer matrix. Application status of UHMWPE fiber such as aerospace, ocean engineering and individual protection is introduced.

Optical nondestructive evaluation for minor debonding defects and interfacial adhesive strength of solid propellant

Minor debonding defects and weak adhesion impair solid propellant integrity, which may cause rocket launch failure. However, it’s difficult to identify these interfacial bonding problems in-situ by the common temporal phase-shifting method due to its inaccurate phase calculation and background noises. In this work, a real-time phase processing method with high-frequency synchronizing trigger technology is proposed to improve phase map quality and anti-interference performance in the phase-shifting process. The method is applied to shearography/ESPI optical nondestructive measurement systems to detect minor debonding defects with minimum diameter of 2 mm and evaluate interfacial adhesive strengths of the bonding layers, respectively. The results show that stable and high-contrast phase maps are obtained in real-time from a large field of view, indicating that the detection capabilities of shearography/ESPI are enhanced via the application of the method. This work would contribute to the in-situ nondestructive evaluation of minor defects and weak adhesion in solid propellants.

Thick elastomeric coating removal using tailored infrared- and infrared-sonication hybrid technology

We report an innovative, cost-effective, and eco-friendly coating removal technology that removes thick polyurethane-based elastomeric coatings without damaging the underlying metal or glass-polymer composite substrates. The developed technology eliminates the need for chemical- or media-based treatments, thus reducing environmental problems such as releasing toxic gases or suspended solid particles in the air. This was achieved using tailored infrared and infrared-ultrasonication treatments of the coated substrates that caused bond failure at the surface coat-substrate interface by selective absorption of IR and/or impinging of the topcoat with the ultrasonication technique. The degraded interfacial adhesion strength then allowed easy removal of the specialty coating with the application of a pull at a certain angle to the substrate-coating interface. The effect of different operating parameters such as time of irradiation, surface temperature, sonication power/intensity was investigated to determine the optimal conditions for coating removal. The treated and untreated coated samples were characterized by DSC, SEM, FTIR, peel-tester, embedded thermocouple/LABVIEW, and infrared thermography techniques. The energy analysis revealed that the fracture energy component was 4× lower on the treated sample than the untreated sample indicating reduced bond strength, which can be explained based on residual thermal stress generated due to the thermal coefficient mismatch and the interfacial cell dislocation. Also, coating from the treated sample could be removed 1.75× faster than from the untreated sample. Based on the cost analysis, the operation cost for this technology is meager compared to conventional and energy-intensive technologies such as laser ablation.

Natural extracts-meditated efficient and electrically responsive bioglues

Bioglues have great potential in the field of biomedical engineering concerning interfacial adhesion. Based on naturally extracted chitosan and benzoic acids, we developed low-viscosity bioglues capable of achieving an efficient and strong interfacial adhesion to wet skin tissues without any additional post-treatment. Owing to the synergy of topology, electrostatic interaction and self-hydrophobization, the adhesive strength could reach as high as 110 kPa when two pieces of fresh porcine skin were adhered together with the bioglues for one minute. Subsequently, we showed that the bioglue-regulated interfacial adhesion was essentially sensitive to external electrical fields with voltages less than 1 V, which might thus cause an electrically responsive adhesion. Likewise, we revealed that the phenol–quinone transition played a dominant role in inducing changes in interfacial adhesion strength modulated by the applied electric fields. By introducing a circuit model to mimic electric stimulation, we further recognized that an electric field of ∼2500 V/m was the threshold required for the electrically regulated phenol–quinone transition. Further, the bioglues were biocompatible, antibacterial and promoted wound healing, making them more suitable for applications in smart interfacial adhesion-related areas like biomedicine, flexible electronics and soft robotics.

WET-Induced Layered Organohydrogel as Bioinspired "Sticky-Slippy Skin" for Robust Underwater Oil-Repellency.

Underwater superoleophobic surfaces featuring anti-oil-fouling properties are of great significance in widespread fields. However, their complicated engineering process and weak interfacial adhesion strength with underlying substrates severely hamper these ideal surfaces toward practical applications. Here, a moss-inspired sticky-slippy skin composed of layered organohydrogel is reported through a one-step wetting-enabled-transfer (WET) strategy, which unprecedentedly integrates robust inherent adhesion with durable anti-oil-fouling properties. The sticky organogel layer can be simply attached to various substrates, from metals and plastics to glass, independent of any surface pretreatment. The slippy hydrogel layer enables stable underwater superoleophobicity and ultralow oil adhesion for diverse kinds of oils. The sticky-slippy skin features outstanding comprehensive properties including easy-pasting, anti-swelling/anti-bending, compatibility with commercial adhesives, acid/alkali resistance, environmental friendliness, and substrate universality. The design strategy with integrated functions provides a clue to accelerate the development of bioinspired multifunctional interfacial materials toward real-world applications.