Effects of UV irradiation on tribological properties of nano‐TiO2 thin films

One‐layer and two‐layer nano‐TiO₂ thin films were prepared on the surface of common glass by sol–gel processing. Water contact angle, surface morphology, tribological properties of the films before and after ultraviolet (UV) irradiation were investigated using DSA100 drop shape analyzer, scanning probe microscopy (SPM), SEM and universal micro‐materials tester (second generation) (UMT‐2MT) friction and wear tester, respectively. The stored films markedly resumed their hydrophilicity after UV irradiation. But UV irradiation worsened tribological properties of the films. After the film was irradiated by UV, the friction coefficient between the film and GCr15 steel ball increased about 10–50% and its wear life shortened about 20–90%. Abrasive wear, brittle break and adherence wear are the failure mechanisms of nano‐TiO₂ thin films. It was believed that UV irradiation increased surface energy of the film and then aggravated adherence wear of the film at initial stage of friction process leading to severe brittle fracture and abrasive wear. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface Modification of Nano－SiO2 by Grafting PMMA／PBA

The surface of nano-SiO2 was modified by being encapsulated with hydroxy-propyl-methyl cellulose (HPMC), and then co-grafted with acrylates. The grafting conditions, such as pH of the medium, and initiator concentration have been studied. The modified nano-SiO2 particles were characterized by TEM, DSC and FT-IR spectra. TEM images show that the surface of the nano-particles has been successfully modified by a thick layer of film-like polymer in this way. The DSC results show that the decomposition temperature of modified nano-particles of SIO2 is 90 ℃ higher than that of grafted-on polymer. According to the FT-IR spectra, It is convinced that poly-methyl methacrylate ( PMMA ) and poly-acrylic butyl-ester ( PBA ) were co-grafted onto the surface of nano-SiO2.     

Interphase/interface modification on the dielectric properties of polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) multilayer films for high‐energy density capacitors

Unique three‐component multilayer films with ATBTATBTA configuration were fabricated using forced assembly multilayer coextrusion for novel dielectric systems. The dielectric breakdown strength, displacement–electric field hysteresis, and dielectric spectroscopy of 65‐layer polycarbonate (PC)/tie/poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐HFP)) were investigated with various tie materials. Three different tie materials, poly(methyl methacrylate) (PMMA), styrene‐co‐acrylonitrile copolymer with 30% acrylonitrile content (SAN30), and poly(ethylene terephthalate‐co‐1,4‐cycohexanedimethylene terephthalate) (PETG) were chosen owing to their various degrees of interaction with either P(VDF‐HFP) or PC. The 65‐layer PC/PMMA/P(VDF‐HFP) films exhibited a 25% enhancement in breakdown properties, 50% higher energy density, 40% smaller hysteresis loop areas, and orders of magnitude slower ion migration relative to the 33‐layer PC/P(VDF‐HFP) control. These property improvements are mainly attributed to the localized interactions at PMMA/P(VDF‐HFP) and PMMA/PC interfaces, forming interphase regions. The modified PMMA/P(VDF‐HFP) interphase region can effectively hinder the migration of impurity ions in P(VDF‐HFP), reducing their mobility within the layer. Additionally, a small fraction of PMMA can lead to slightly increased dielectric constant of the composite films owing to strong interaction between PMMA and P(VDF‐HFP). The other two systems with PETG and SAN30 as tie layers exhibited marginal improvements in dielectric properties owing to their weaker interactions with the P(VDF‐HFP) layers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 978–991     

Surface and interface characterization of polyester‐based polyurethane/nano‐silica composites

Polyester‐based polyurethane/nanosilica composites were prepared via in situ polymerization and investigated by contact angle measurement, transmission electron microscopy (TEM), atomic force microscopy (AFM) and peel testing in an Instron testing machine. The contact angle and surface free energy results show that nanosilica tended to enrich at the interface between nanocomposite polymers and the substrates, TEM indicated that nanosilica particles were evenly dispersed in the bulk and AFM demonstrated that nanoparticles were located at both the surfaces and interfaces of nanocomposite polymers and that the roughness of both the surfaces and interfaces had a decreasing tendency as the nanosilica content increased, as did the adhesion strength between the nanocomposite polymers and substrates. Copyright © 2003 John Wiley & Sons, Ltd.     

Superhydrophilic/superhydrophobic surfaces fabricated by spark‐coating

In this study, the authors researched the preparations of superhydrophilic/superhydrophobic surfaces on commercial cup stock polyethylene coated papers by using sparked aluminum nanoparticles deposited on substrates through a sparking process. In this stage, the surface was porous and showed superhydrophilic properties. The samples were then annealed in air at various temperatures and some transformed to superhydrophobicity. It is well known that a suitable roughness in combination with low surface energy has been required to obtain superhydrophobic surfaces. Therefore, it is believed that during annealing process, when polyethylene is diffused from the substrate through the nanoparticle films and the superhydrophobic characteristics were created. The scanning electron microscope images showed that the film surfaces had a fluffy structure for both the as‐deposited and the annealed samples. However, the atomic force microscopy phase images showed completely different surface properties. Moreover, the X‐ray photoelectron spectroscopy spectra showed different surface chemical compositions. The experimental results revealed that the working temperature to produce superhydrophobic surfaces depended on the sparked film thickness. Furthermore, in order to prove the assumption explained above, glass and poly (methyl methacrylate) were also used as substrates.     

The oxidation‐treated interface on tribological properties of carbon fibers‐reinforced PTFE composite under oil‐lubricated condition

The effect of air oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil‐lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF–PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air‐oxidated composites. X‐ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen‐containing groups on CF surfaces was largely increased. The increase in the amount of oxygen‐containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix and large scale rubbing‐off of PTFE was prevented, therefore, the tribological properties of the composite were improved. Copyright © 2009 John Wiley & Sons, Ltd.     

Isoconversional method to explore the cure reaction mechanisms and curing kinetics of DGEBA/EMI‐2,4/nano‐SiC system

The curing kinetics of the diglycidyl ether of bisphenol‐A (DGEBA)/2‐ethyl‐4‐methylimidazole (EMI‐2,4)/nano‐sized carborundum (nano‐SiC) system was studied by means of nonisothermal differential scanning calorimetry (DSC). An isoconversional method of kinetic analysis yields a dependence of the effective activation energy E on the extent of conversion that decreases initially, and then increases as the cure reaction proceeds. The variations of E were used to study the cure reaction mechanisms, and the Shrinking Core Model was used to study the resin–particle reaction. The results show that the presence of nano‐SiC particles prevents the occurrence of vitrification, as well as inhibits the cure reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 371–379, 2006     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.     

A green and efficient method for synthesis of benzimidazoles using nano‐Fe3O4 in PEG‐400/H2O aqueous system under ambient conditions at room temperature

In this paper, a green and facile protocol was described which was efficient for synthesis of benzimidazoles using nano‐Fe₃O₄ catalyst with continuous bubbling of air as the oxidant in PEG‐400/H₂O aqueous system at room temperature. This protocol afforded the target products in good to excellent yields and the catalytic system could be recycled and reused without significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication of Al/AlN nano‐composite layers by friction stir processing of 6061 Al‐T6 substrate

Friction stir processing was employed for the production of Al/AlN nano‐composite layers on a 6061 Al‐T6 substrate. Nano‐sized AlN powder was inserted in a groove in the middle length of the substrate. Defect‐free layers were achieved using tool rotation and substrate advancing speeds in the range of 900–1400 rpm and 63–310 mm/s, respectively. Subsequent passes were conducted to break‐up AlN clusters that formed in a non‐uniform fashion after initial pass. The grain size of aluminum matrix was found to decrease by the introduction of AlN powder. A nano‐composite layer with near uniform dispersion of nano‐sized AlN reinforcements with a ~9.6% volume fraction was achieved in a matrix of fine dynamically restorated Al grains with a mean size of ~2.5 µm after three subsequent passes. This layer showed an average micro hardness value of ~164 HV (much greater than ~103 HV of the underlying substrate). In addition, the nano‐composite layer exhibited superior dry sliding wear performance against hardened steel compared to that of 6061‐T6 substrate. Increasing tool rotation and substrate advancing speeds were found to decrease the AlN content of the processed layer possibly due to increasing in powder scattering by the pin tool. This was associated with a decrease and increase in hardness values and wear‐loss data, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface modification for nano‐lignocellulose fiber through vapor‐phase‐assisted surface polymerization

This study addresses the inherent issues surrounding surface modification methods of nanofibers and proposes an environmentally friendly and less toxic strategy for the surface modification of hydrophilic nanofiber. From the continuation of our previous work, which discussed the easy production of nanofiber (average size: 127 nm) from oil palm mesocarp fiber (OPMF), in this work, the surface of nanofibers (M‐IL‐OPMF) were modified through vapor‐phase‐assisted surface polymerization (VASP) to improve the affinity of interface between the polymer grafted M‐IL‐OPMF and non‐polar matrix. VASP of ε‐caprolactone was successfully proceeded from the [M‐IL‐OPMF] at 70 °C for 24 h and 72 h, and compositions were estimated to be 35.7% fiber/64.3% polymer and 27.8% fiber/72.2% polymer. To confirm the grafting of PCL, size‐exclusion chromatography (SEC) and Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetry (TG), and dispersibility test in hydrophobic solvent were carried out. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2575–2580     

Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Rf‐GDOES analysis of composite metal/ceramic electroplated coatings with nano‐ to microceramic particles' size: issues in plasma sputtering of Ni/micro‐SiC coatings

Ni matrix composite coatings reinforced with nano‐ and microceramic particles were analyzed by radio frequency glow discharge optical emission spectrometry (Rf‐GDOES). An interesting phenomenon related to the sputtering and excitation modes of this technique was observed. During plasma sputtering with Rf‐GDOES, the micro‐SiC particles were detached from metal matrix and did not contribute to the analytical signals. The same was not found in composite coatings containing nanoceramic particles. This anomalous behavior was confirmed by atomic force microscopy (AFM) investigation and scanning electron microscope (SEM) observations into Rf‐GDOES craters that showed the presence of residual non‐sputtered microparticles. Various attempts were done in order to minimize this problem, mainly by varying the analysis parameters of the used instrumentation, but without any relevant success. Some suggestions were then proposed for explaining the observed phenomenon, moreover possible solutions (e.g. by using a strong magnetic field or changing plasma gas to be more energetic) are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

A ToF‐SIMS investigation of a buried polymer/polymer interface exposed by ultra‐low‐angle microtomy

The interfacial region of a model multilayer coating system on an aluminium substrate has been investigated by high‐resolution time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Employing ultra‐low‐angle microtomy (ULAM), the interface between a poly(vinylidene difluoride) (PVdF)‐based topcoat and a poly(urethane) (PU)‐based primer ‘buried’ >20 µm below the PVdF topcoat's air/coating surface was exposed. Imaging ToF‐SIMS and subsequent post‐processing extraction of mass spectra of the ULAM‐exposed interface region and of the PVdF topcoat and PU primer bulks indicates that the material composition of the polymer/polymer interface region is substantially different to that of the bulk PVdF and PU coatings. Analysis of the negative ion mass spectra obtained from the PVdF/PU interface reveals the presence of a methacrylate‐based component or additive at the interface region. Reviewing the topcoat and primer coating formulations reveals that the PVdF topcoat formulation contains methyl methacrylate (MMA)–ethyl acrylate (EA) acrylic co‐polymer components. Negative ion ToF‐SIMS analysis of an acrylic co‐polymer confirms that it is these components that are observed at the PVdF/PU interface. Post‐processing extraction of ToF‐SIMS images based on the major ions of the MMA–EA co‐polymers reveals that these components are observed in high concentration at the extremities of the PVdF coating, i.e. at the polymer/polymer interface, but are also observed to be distributed evenly throughout the bulk of the PVdF topcoat. These findings confirm that a fraction of the MMA–EA acrylic co‐polymers in the formulation segregate to the topcoat/primer interface where they enhance the adhesive properties exhibited by the PVdF topcoat towards the underlying PU primer substrate. Copyright © 2004 John Wiley & Sons, Ltd.     

XPS survey spectra simulation of nano‐structured surfaces

We have developed a software tool for the generation of survey spectra in X‐ray photoelectron spectroscopy (GOSSIP) to simulate wide spectra in the range 200–1500 eV from nano‐structured surfaces. It is based on linear combination of delta layers spectra with the atomic spectra of the elements or compounds of the surface to be simulated. The set of delta layers to reproduce any model is a 200‐file database of thin layers regularly buried up to a depth of 40 nm and has been generated with QUASES^™. The atomic spectra that constitute a second database have themselves been determined with QUASES^™ from experimental spectra of the elements or compounds in pure form. The principle of GOSSIP is described. Then the generation process is validated by comparison with experimental data for simple rectangular in‐depth distribution of elements. Copyright © 2009 John Wiley & Sons, Ltd.     

Hybrid organic–inorganic block copolymer nano‐objects from RAFT polymerization‐induced self‐assembly

A simple route to organic–inorganic (O/I) nano‐objects with different morphologies through polymerization‐induced block copolymer self‐assembly is described. The synthetic strategy relies on the chain‐extension of polyhedral oligomeric silsesquioxanes (POSS)‐containing macro‐CTA (PMAiBuPOSS₁₃ and PMAiBuPOSS₁₉) with styrene at 120 °C in octane, a selective solvent of the POSS‐containing block. The polymerization system was proven to afford a plethora of O/I nano‐objects, such as spherical micelles, cylindrical micelles, and vesicles depending on the respective molar masses of the PMAiBuPOSS and polystyrene (PS) blocks. The cooling procedure was also proven to be a crucial step to generate particles with a unique morphology. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4558–4564     

Comparative study of microstructure and tribological behavior of TiC/a‐C:H and a‐C:H coatings in a sand‐dust environment

TiC/a‐C:H and a‐C:H nanocomposite coatings were prepared on AISI 440C steel substrates using magnetron sputtering process. A comparative study was made on their composition and microstructure by Raman spectroscopy and high‐resolution transmission electron microscopy (HRTEM). The tribological properties of two types of carbon‐based coatings were investigated by pin‐on‐disc tribometer under the sand‐dust conditions concerning the influence of applied load, amount of sand and sand particle sizes. The results show that these carbon‐based coatings exhibited high tribological performance with low friction coefficient and wear rate under the sand‐dust environments. However, the TiC/a‐C:H coatings exhibit relatively higher fluctuant friction coefficient as well as higher wear rate in comparison with the a‐C:H coatings under sand‐dust environments. The formation of nanocrystalline hard TiC phase distributed in amorphous carbon matrix decreased the residual stress but significantly increased the hardness and Young's modulus of TiC/a‐C:H coatings, and consequently caused a relatively higher abrasive and fatigue wear loss under the sand‐dust conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

The tribological performance of fullerene‐like hydrogenated carbon films under ionic liquid lubrication

Fullerene‐like hydrogenated carbon films were deposited on Si substrate by plasma‐enhanced chemical vapor deposition. The microstructures of films were characterized by high‐resolution transmission electron microscopy and Raman spectrum. The tribological performance of films was tested by reciprocating ball‐on‐disc tester under 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid. The surface morphology and chemical composition of wear tracks and wear rates were investigated by optical microscope, X‐ray photoelectron spectroscopy, and 3D surface profiler. The results indicated that the film with a typical fullerene‐like structure embedded into the amorphous sp² and sp³ carbon networks could be prepared successfully, and the film shows a higher hardness (26.7 GPa) and elastic recovery (89.9%) compared with the amorphous carbon film. Furthermore, the film shows a lower friction coefficient at low contact load and friction frequency, and excellent wear‐resistance performance at high load and frequency under ionic liquid lubrication. Meanwhile, the wear life of fullerene‐like hydrogenated carbon films could be improved significantly using ionic liquid as a lubrication material. Copyright © 2015 John Wiley & Sons, Ltd.     

Improvement in gas separation properties of a polymeric membrane through the incorporation of inorganic nano‐particles

The present work tries to introduce a high‐performance nano‐composite membrane by using polydimethylsiloxane (PDMS) as its main polymer matrix to meet some specific requirements in industrial gas separations. Different nano‐composite membranes were synthesized by incorporating various amounts of nano‐sized silica particles into the PDMS matrix. A uniform dispersion of nano‐particles in the host membranes was obtained. The nano‐composite membranes were characterized morphologically by scanning electron microscopy and atomic force microscopy. Separation properties, permeability, and ideal selectivity of C₃H₈, CH₄, and H₂ through the synthesized nano‐composite membranes with different nano‐particle contents (0.5, 1, 1.5, 2, 2.5, and 3 wt%) were investigated at different pressures (2, 3, 4, 5, 6, and 7 atm) and constant temperature (35°C). It was found out that a 2 wt% loading of nano‐particles into the PDMS matrix is optimal to obtain the best separation performance. Afterwards, sorption experiments for the synthesized nano‐composite membranes were carried out, and diffusion coefficients of the gases were calculated based on solution‐diffusion mechanism. Gas permeation and sorption experiments showed an increase in sorption and a decrease in diffusion coefficients of the gases through the nano‐composite membranes by adding nano‐particles into the host polymer matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

First‐principles study of the TiN(111)/ZrN(111) interface

The TiN(111)/ZrN(111) interface was studied by first‐principles method to provide the theoretical basis for developing the TiN/ZrN coatings. Twelve geometry structures of TiN(111)/ZrN(111) interfaces were established. The calculated interfacial work of adhesion reveals that the N‐terminated TiN/N‐terminated ZrN interface with TL site shows the strongest stability. For this TiN(111)/ZrN(111) interface, the results of the partial density of state indicate that the chemical bonding at the interface appeals both ionic and covalent characteristic, which is same as that in the bulk materials. The partial density of states for Zr, Ti, and N atoms at the interface are very similar with those in the bulk, which reveals that the electronic structure transition at the interface is smooth. The results of charge density and charge density difference demonstrate that the lost charge of Ti atom is larger than that of Zr atom, indicating that TiN is more ionic than ZrN. Calculations of the work of fracture indicate that the mechanical failure of the ZrN(111)/TiN(111) interface will take place at the interface. Besides that, the calculation result of the TiN(111)/ZrN(111) interface implies that the TiZrN₂ phase might be formed at the interface because the contacting of the N―N bond is the most stable.