Adhesion property of AlCrNbSiTi high-entropy alloy coating on zirconium:experimental and theoretical studies

Experimental scratch tests and first-principles calculations were used to investigate the adhesion property of AlCrNbSiTi high-entropy alloy(HEA)coatings on zirconium substrates.AlCrNbSiTi HEA and Cr coatings were deposited on Zr alloy substrates using multi-arc ion plating technology,and scratch tests were subsequently conducted to estimate the adhesion property of the coatings.The results indicated that Cr coatings had better adhesion strength than HEA coatings,and the HEA coatings showed brittleness.The special quasi-random structure approach was used to build HEA models,and Cr/Zr and HEA/Zr interface models were employed to investigate the cohesion between the coatings and Zr substrate using first-principles calculations.The calculated interface energies showed that the cohesion between the Cr coating and the Zr substrate was stronger than that of the HEA coating with Zr.In contrary to Al or Si in the HEA coating,Cr,Nb,and Ti atoms binded strongly with Zr substrate.Based on the calculated elastic constants,it was found that low Cr and high Al content decreased the mechanical performances of HEA coatings.Finally,this study demonstrated the utilization of a combined approach involving first-principles calculations and experimental studies for future HEA coating development.

Determination of interfacial adhesive properties for polymeric film by blister test

The interfacial adhesive properties ofpolypropylene/stainless steel were studied by the blister test. The polypropylene film with a squared free-standing window was pressured by oil from one side of film. The corresponding deformation field was observed by a digital speckle correlation method. The experimental results show that the squared film deforms and debonds from stainless steel with the increase of pressure. The debonding of the squared film in initiates from the center of edge and extends to the comer, and then the deformation of film evolves from square to circle shape. The interfacial adhesive energy of polypropylene/stainless steel is （22.60±1.55） J/m2, which is in agreement with that measured by film with a circular window.

Study on ASTM Shear-loaded Adhesive Lap Joints

Finite element analyses and experiments are conducted to analyze the mechanical behavior of ASTM shear-loaded adhesive lap joints. Adhesive is characterized for the stress-strain relation by comparing the apparent shear-strain relations obtained from finite element analysis and experiments following ASTM D 5656 Standard. With the established stress-strain relation, two failure criteria using equivalent plastic strain and J-integral are adopted to predict the failure loads for joint specimens following ASTM D 5656 and ASTM D 3165 Standard, respectively. Good correlation is found between the finite element results and the experimental results. The strength of ASTM D 3165 specimens with debonding defects is also studied. Calculation results shows that experiment data following the standards provide only relative material constants, such as apparent shear modulus and strengths. Further investigation is required to find out the engineering properties needed for actual joint design. For the specimens with debonding defects, the locations of defects have great effects on their load bearing ability.

Surface adhesive properties of continuous PBO fiber after air-plasma-grafting-epoxy treatment

It was found that air dielectric barrier discharge(DBD) plasma contributed to the grafting of epoxy resin onto continuous PBO fiber surface. This air-plasma-grafting-epoxy method yielded a noticeable enhancement in the interfacial adhesion between PBO fiber and thermoplastic matrix resin, with the interlaminar shear strength of the resulting composites increased by 66.7%. DSC and FTIR analyses were then used to study the curing behavior of epoxy coating on PBO fiber surface, deduce the possible grafting reactions and investigate the grafting mechanism. More importantly, TGA measurement showed that the grafting of epoxy onto PBO fiber had almost no effect on the composite heat resistance, and there was more thermoplastic matrix resin adhering to the fiber surface; the latter could also be clearly found in the SEM photos. Thereby, the air-plasma-grafting-epoxy treatment was proved to be an effective method for the improvement of continuous PBO fiber surface adhesive properties.

Enhancing surface adhesion of polytetrafluoroethylene induced by two-step in-situ treatment with radiofrequency capacitively coupled Ar/Ar+CH_(4)+NH_(3) plasma

Although some progress in plasma modification of the polytetrafluoroethylene(PTFE) surface has been made recently,its adhesion strength still needs to be further improved.In this work,the surface of a PTFE sample was treated with a two-step in-situ method.Firstly,the PTFE surface was treated with capacitively coupled Ar plasma to improve its mechanical interlocking performance;then,Ar+NH_(3)+CH_(4) plasma was used to deposit an a-CNx:H cross-linking layer on the PTFE surface to improve the molecular bonding ability.After treatment,a high specific surface area of 2.20 and a low F/C ratio of 0.32 were achieved on the PTFE surface.Its surface free energy was increased significantly and its maximum adhesion strength reached77.1 N·10 mm^(-1),which is 56% higher than that of the single-step Ar plasma-treated sample and32% higher than that of the single-step Ar+CH_(4)+NH_(3) plasma-treated sample.

Advances in studies of the tribological behavior of molecular deposition films

An overview of the advances in studies on tribology of molecular deposition （MD） films is presented here to summarize the studies of nanofrictional properties, adhesion, wear and mechanical behavior, as well as the molecular dynamics simulation of nanotribological properties of the film in the last decade. Some key research topics which need to be investigate further are addressed.

Influence of Backbone Structure on Properties of Directly Polymerized Phenoxy Resins from Epichlorohydrin and Various Aromatic Dihydric Phenols Monomers

A series of phenoxy resins was directly prepared through the polymerization of each of the various aromatic dihydric phenols and epichlorohydrin.FTIR and 1H NMR spectra were recorded to characterize the structures of the re-sins.The GPC curves were used to determine the molecular weight distribution.In addition,the thermal properties of the resins were studied with differential scanning calorimetry（DSC）and thermal gravimetric analysis（TGA）.The thermal stabilities of the polymers increased with the content of the benzene ring,pendant group increasing or biphenyl groups emerging.The adhesive properties of the polymers were evaluated in terms of the lap shear strength with Fe-Fe adherends.The fracture mechanisms were determined by SEM observation and it was found that there was an important participation of cohesive fracture mechanisms.Also,it has been demonstrated that the extension of these micro-cohesive mechanisms is directly correlated with the adhesive strength.According to these results,the phenoxy resin containing biphenyl groups presented a higher adhesive strength and could improve the adhesive property of the epoxy/phenoxy system to a certain extent.

PPC-based Reactive Hot Melt Polyurethane Adhesive(RHMPA)--Efficient Glues for Multiple Types of Substrates

Tens of billion metric tons of anthropogenic CO_2 discharged from the burning of fossil fuels lead to an enormous environmental and resource burden. It is charming to transform CO_2 to desirable, economical chemicals and materials. Poly（propylene carbonate）（PPC） is an emerging CO_2-based material. Herein, we report the design, synthesis and characterization of the reactive hot melt polyurethane adhesive（RHMPA） based on PPC polyol. The resultant RHMPAs exhibit good adhesion properties to multiple substrates including plastics（PC, PMMA, ABS） and metals（aluminium, steel）, which is comparable to or even better than conventional RHMPAs prepared from petro-based polyol. Furthermore, the PPC-based RHMPAs have tunable mechanical properties, and are thermally stable in the typical working range of bonding process（up to 270 °C）. The study is expected to expand the applications of PPC and provide a new type of CO_2-based renewable and eco-friendly materials.

PREPARATION, CHARACTERIZATION AND ADHESIVE PROPERTIES OF DI-AND TRI-HYDROXY BENZOYL CHITOSAN NANOPARTICLES

Modified chitosans with 3,4-di-hydroxy benzoyl groups （CS-DHBA） and 3,4,5-tri-hydroxy benzoyl groups （CS- THBA） were synthesized and their nanoparticles were prepared via ionic crosslinking by tripolyphosphate （TPP）. The chemical structure and degree of substitution （DS） of di- and tri-hydroxy benzoyl chitosans are determined by FTIR and IH- NMR spectroscopy. The morphology of particles, size distribution and zeta potential of nanoparticles were studied using transmission electron microscopy （TEM） and dynamic light scattering （DLS）, respectively. The mean diameters of particles of CS-DHBA and CS-THBA nanoparticles were 144 nm and 112 nm, respectively. It was found that the particles size decreased slightly with decreasing the degree of substitution and increasing degree of deacetylation （DD）, due to increasing of ionic crosslinking of ammonium ions and polyanions of tripolyphosphate. The TEM photographs of CS-DHBA show that these particles are spherical in shape, but the particles of CS-THBA show some aggregation. In addition, the solubility and the mechanical properties of the prepared modified chitosans and their nanoparticles were evaluated for bio-adhesive and biomedical application. The results of solubility tests indicated that, the CS-DHBA and CS-THBA have higher solubility at pH 〉 7 comparing to CS. Also the CS-DHBA, CS-THBA and their nanoparticles showed a significant adhesive capacity and enhanced tensile strength and tensile modulus.

Multifunctional hydrogels for chronic wounds repairing

Because of their tissue-like mechanical performances,high biocompatibility,and adjust-able functionality,hydrogels have become increasingly attractive materials for promoting wound healing.Chronic wounds include burn,diabetic,and infected wounds.Unlike common incision wounds,chronic wounds are more challenging to heal.To meet the clinical needs,multifunctional hydrogels should be fabricated and investigated.To guide future studies on the fabrication of hydrogel-based chronic wound dressings,a review of advanced multifunctional hydrogels is necessary.Various hydrogels with advanced properties,such as antibacterial,antioxidant,bioadhesive,anti-inflammatory,and wound healing properties,that can be used for skin burn wounds and diabetic wounds are summarised.Lastly,the prospects of advanced hydrogels for wound healing are elaborated.

Simulation of the effect of hydrate adhesion properties on flow safety in solid fluidization exploitation

During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues arising during the transport process,such as the blockage of pipelines and equipment,have attracted considerable attention.This study aims to investigate the impact of hydrate adhesion features,including agglomeration,cohesion,and deposition,on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation.We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method(CFD-DEM)for the multiphase mixed transport in solid fluidization exploitation.An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained.The conclusions obtained are as follows.Under the same operating conditions,a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces;adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings.Hydrate adhesion lowers the height of the solid-phase moving bed,while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe.These particles tend to form a deposit bed rather than a moving bed,which reduces the effective flow area of the pipeline and increases the risk of blockage.

A review on tribology of polymer composite coatings

Self-lubricating polymer composite coatings,with tailorable tribological and mechanical properties,have been widely employed on mechanical parts to reduce friction and wear,which saves energy and improves the overall performance for applications such as aerospace satellite parts,shafts,gears,and bushings.The addition of functional fillers can overcome the limitations of single-polymer coatings and extend the service life of the coatings by providing a combination of low friction,high wear resistance,high load bearing,high temperature resistance,and high adhesion.This paper compares the heat resistance,and the tribological and mechanical properties of common polymer matrices,as well as the categories of functional fillers that improve the coating performance.Applicable scopes,process parameters,advantages,and limitations of the preparation methods of polymer coatings are discussed in detail.The tribological properties of the composite coatings with different matrices and fillers are compared,and the lubrication mechanisms are analyzed.Fillers reduce friction by promoting the formation of transfer films or liquid shear films.Improvement of the mechanical properties of the composite coatings with fillers of different morphologies is described in terms of strengthening and toughening mechanisms,including a stress transfer mechanism,shear yielding,crack bridging,and interfacial debonding.The test and enhancement methods for the adhesion properties between the coating and substrate are discussed.The coating adhesion can be enhanced through mechanical treatment,chemical treatment,and energy treatment of the substrate.Finally,we propose the design strategies for high-performance polymer composite coating systems adapted to specific operating conditions,and the limitations of current polymer composite coating research are identified.

Environmental Concern of Using Coal Tar in Road Engineering and Its Possible Alternatives

Coal tar,a by-product from the destructive distillation of coal in coking oven,is widely used in road engineering for its excellent adhesion and fuel resistance properties,especially for pavement surface treatments in gas stations and airports. However,coal tar has a high Polycyclic Aromatic Hydrocarbons (or PAHs) content,which makes it toxic. In 1985,the International Agency for Research on Cancer (IARC) has proved that coal tar is carcinogenic to humans. Research showed that Coal Tar-based Sealers (CTS) contribute to the majority of PAHs pollution in the water environment.Because of this environmental concern,CTS are not allowed in many developed countries in the USA and Europe. In contrast,coal tar is still used for road engineering in China and is even used increasingly.This paper gives a literature review on the general information and research about environmental concern of using coal tar in road engineering. Based on the review,some possible alternatives to replace coal tar are described. These alternatives include nano-clay/epoxy modified bitumen/bitumen emulsion and waterborne polyurethane/epoxy resin,which are environmental friendly. They have the potential to perform as well as CTS,and even better in some special applications.

Interface adhesion properties characterization of sulfide electrode materials by the combination of BOLS and XPS

Although sulfide electrode materials in lithium battery systems have been intensively investigated due to their low-cost, high theoretical specific capacity, and energy density, there are few studies fousing on the adhesion properties, including the physical origin of hetero-coordination resolved interface relaxation, binding energy and the energetic behavior, and even the accurate quantitative information. In this paper, we present an approach for quantifying the interface adhesion properties of sulfide electrode materials resolved by the combination of bond order-length-strength theory(BOLS) and X-ray photoelectron spectroscopy(XPS), which has enabled clarification of the interface adhesion nature. The results show that the Cu 2p, Fe 2p, and S 2p electrons of Cu S and FeS_(2) compounds shift negatively due to the charge polarization of the conduction electrons of the heteroatoms, while Mo 3d, Sn 3d electrons of Mo S2 and Sn S2 and the C 1 s and S 2p electrons of CS compound shift positively due to the quantum trapping. It is noted that the exact interface adhesion energies of Cu S is 3.42 J m^(-2), which is consistent with the calculation result. The approach can not only clarify the origin of the interface adhesion properties of sulfide electrode materials,but also derive their quantification information from atomistic sites.