Effects of experimental variables on PMMA nano-indentation measurements

This work aims to investigate the effects of experimental variables on nano-indentation measurements on PMMA. A wide range of conditions, including different load levels, loading rates, holding times and unloading rates were employed to examine the sensitivity of nano-indentation measurements to the selected experimental variables. The test results indicate that the elastic modulus and hardness of PMMA are approximately load-level invariant. However, they are sensitive to the loading rate, holding time and unloading rate. Both elastic modulus and hardness increase with increasing loading rate, while increasing holding time leads to decreasing elastic modulus and hardness. Moreover, the unloading rate has almost no obvious effect on the hardness of PMMA, while the opposite is true for elastic modulus.     

Microstructural Characterization and Mechanical Property of Iridium Coating Produced by Double Glow Plasma

Ir is the most interesting as an effective oxygen diffusion barrier for super high-temperature structural materials. In this study, an Ir coating, approximately 7 μm thick, was deposited onto Mo substrate by double glow plasma at substrate temperature of about 1,120 K in an argon atmosphere. The crystal orientation, morphology and mechanical property of the Ir coating were investigated by XRD, SEM, AFM, TEM, nanoindentation and scratch test. The results indicated that the (220)-oriented Ir coating was composed of the columnar grains. The surface roughness of the Ir coating was higher than that of the substrate. The hardness and the elastic modulus of the Ir coating were about 9.5 and 340 GPa, respectively. The coating had a high hardness due to the sub-micrometer size grains. The coating had good scratch resistance due to the strong adhesion of the coating to the substrate.     

A study of surface changes of wood-polypropylene composites as the result of exterior weathering

Outdoor applications of composites raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The weathering resulted in considerable colour fading of the composites. Composites containing darker colour pigments had better colour stability. Scanning electron microscopy analysis revealed that surface cracks caused by weathering in a wood-polypropylene composite having a higher polypropylene content were less abundant, and the deterioration of the surface layer was lower compared to composites containing less polymer. Measurements of melting temperatures by differential scanning calorimetry gave a consistent picture of polypropylene degradation in the surface layer. After weathering, a decrease in Charpy impact strength was found for composites characterised by higher moisture absorption.     

Grey relational analysis for optimization of wear parameters and surface roughness on nano composite coating

The higher wear resistance of Ni based nano composite coatings makes them potential replacement in protecting the substrate materials. The role of surface roughness of the coating along with wear parameters on the specific wear rate, pin temperature, and COF are addressed in the present study. The use of hard nano Al₂O₃ particles found significant role in increasing the resistance to wear for Ni matrix coatings on Al6061 material. The resistance to dislocation offered by these nano Al₂O₃ particles and smear out of debris with plastic deformation indicated abrasive and adhesive nature of wear mechanism in combination. The optimization of wear parameters are carried out by surface response method based grey relation analysis. The normal load applied onto the pin has significant influence on the specific wear rate and temperature rise in the pin. The surface roughness of the coating has also found instrumental in the higher pin temperature and friction coefficient.     

Surface‐interface microstructures and binding strength of cathodic arc ion plated TiCN coatings on YT14 cutting tools

A titanium carbonitride (TiCN) coating was deposited on YT14 cutting tool by using a CAIP (cathodic arc ion plating). The surface‐interface morphologies, chemical compositions, and phases of TiCN coatings were observed by using a FESEM (field emission scanning electron microscopy), EDS (energy dispersive spectroscopy), XRD (X‐ray diffraction), respectively, and the bonding energy, surface roughness, and bonding strength were characterized with an XPS (X‐ray photoelectron spectroscopy), AFM (atomic force microscope), and scratch test, respectively. The results show that the phases of the TiCN coating are primarily composed of TiN, TiC, and amorphous C, of which the TiC and TiN increases the coating hardness, and the amorphous C atom improves friction and lubrication properties of the coating. The effect of CAIP on the topography of the TiCN coating is at nano‐scale, the Ti and N atoms are enriched in the coating at the bonding interface, and the part of chemical elements are diffused in the gradual transformation layer. The bonding form of the TiCN coating interface is primarily composed of mechanical combination, accompanying with slight metallurgical combination, and the bonding strength is characterized with 60.85 N by scratch test. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of Solvent Effect on Mechanical Properties of Poly(ether ether ketone) Using Nano-indentation

Poly (ether ether ketone)(PEEK) is a high-performance semi-crystalline thermoplastic polymer.Exposure of the polymeric surface to solvents can have a strong effect like softening/swelling of polymeric network or dissolution.In this study, nano-indentation analysis was performed to study the effect of acetone on the surface mechanical properties of PEEK using different exposure time.The experiments were performed with a constant loading rate (10 nm/s) to a maximum indentation displacement (1000 nm).A 30-second hold segment was included at the maximum load to account for any creep effects followed by an unloading segment to 80% unloading.The indentation hardness and the elastic modulus were computed as a continuous function of the penetration displacement in the continuous stiffness mode (CSM) indentation.The experimental data showed that the peak load decreased from ~5.2 mN to ~1.7 mN as exposure time in solvent environment increased from 0 to 18 days.The elastic modulus and the hardness of PEEK samples also displayed a decreasing trend as a function of exposure time in the solvent environment.Two empirical models were used to fit the experimental data of hardness as a function of exposure time which showed a good agreement with the experimental values.     

Hardness Equation for Ormosils

Hardness of ormosils coating on various kinds of substrates is important, and by considering recent progresses in understanding the hardness of ionic crystals or covalent crystals, new hardness equations for calculating the hardness of glasses or ormosils from chemical compositions were derived. When we applied an indenter to the surface of glass or sol-gel coatings, the surface of indenter is a declined one to the flat surface of glass or coating, thus the applied force should be analyzed by using the shear modulus, S, and Young's modulus, E. This is now well accepted for the analysis of hardness of ionic or covalent bonding inorganic materials. For example, by considering the binding energy and plastic deformation, Gilman showed that Hv of NaCl crystal can be calculated by an equation including elastic stiffness which indicated a good agreement between calculated and observed value. For covalent crystals he reported that the strength of chemical bonds could be correlated with the glide (shear) activation energy for covalent crystals quantitatively. These explanations are basically applied to the hardness of silicate glasses and ormosils. By considering both shear modulus and Young's modulus we have derived equations for calculating the hardness of glasses or ormosils from chemical composition, which includes packing density of atoms and bond energy per unit volume has been taken account. The agreements between calculated and observed hardness values for ormosils were comparatively good.     

Outdoor and accelerated weathering tests for polypropylene and polypropylene/talc composites: A comparative study of their weathering behavior

In this study, the comparisons of degradation behavior of polypropylene(PP) and PP/talc composites were carried out with one outdoor weathering test and three accelerated weathering (xenon, metal halide and carbon arc lamps) tests, respectively. The outdoor exposure vigorously advanced these degradations with the lowest amount of UV exposure energy. It was found that the degradation rates were affected by the visible light intensity in the light sources. In the case of the existence of talc compound, the degradation was synergistically accelerated by the exposures of the sunshine, the xenon and the metal halide lamps having higher visible light intensities. In addition, the degradations of the PP and the PP/talc composites were found to be synergistically accelerated by sunlight exposure and the acid rain, too.     

Study of the structure and mechanical properties of hexagonal BaTiO3 thin films prepared by sol鈥揼el processing

Hexagonal barium titanate (HBT) thin films were prepared on borosilicate plate substrates via sol–gel method using the dip-coating process. The structure, texture and morphology of the thin film were analyzed by X-ray diffraction, atomic force microscopy, nanoindentation technique, and transmission electron microscopy. The results showed that the thin film annealed at 700?°C crystallized with BaTiO₃ hexagonal phase and traces of Ba₂TiO₄ (secondary phase). The nanoparticles and the RMS roughness of the sample treated at 700?°C presented high values when compared with those thermally treated at lower temperatures. The hardness and Youngs??modulus of the thin films increased with increasing in grain size, and the thin film annealed at 700?°C with crystallite size about 10?nm presented multiple “pop-in??events during nano-indentation loading curves. The annealing temperature, growth size and surface roughness were discussed in connection with the HBT mechanical properties.     

The structure and properties of polymer-metallic coating interphase

The structure of the surface layer in polymers (LDPE and PET) decorated with a thin metal (gold and platinum) layer was studied after their deformation under different conditions. It was found that relatively thick coatings debonded from the polymer substrate during tensile drawing. Debonding was observed at low tensile strains (below 20–30%). During the further drawing of a polymer, a regular microrelief typical of deformable “rigid coating on a soft substrate” systems appeared on its surface. This phenomenon is explained by the fact that the debonding metal coating uncovers not the surface of the pure polymer but a certain modified layer, which has a higher elastic modulus than the pure polymer. The formation of this layer is associated with the inclusion of metal atoms into the polymer during the metal decoration by plasma immersion ion deposition. As a result of this inclusion, a modified layer, which has a higher glass transition temperature, a higher elastic modulus, and other mechanical properties, is formed between the coating and the polymer.     

Weatherability and wear resistance characteristics of plasma fluoropolymer coatings deposited on an elastomer substrate

The weathering characteristics of thin film formed from plasma polymerisation of perfluoro(methylcyclohexane) on an EPDM substrate under cold plasma process operated at 13.56 MHz was investigated using an ATLAS Ci 3000 Xenon weatherometer. The effects of weathering conditions on the chemical composition of the substrate and the coating were examined using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-ray photoelectron spectroscopy (XPS). The wear behaviour was examined using scanning electron microscopy (SEM). The change in the surface morphological behaviour of the coating indicates that the mending line of the patch-wise coating deposition or the fissure/crack line of the coating is particularly sensitive to the initiation of decomposition. FTIR and XPS spectroscopic investigations confirm that under humid and UV conditions, elimination of fluorine and introduction of new oxygen-containing functional groups play predominant role in the decomposition of the coating. Plausible mechanisms of degradation for the elastomer and the coating have been proposed. The coated substrate shows superior abrasion resistance characteristics with respect to the neat elastomer. The adhesion between the substrate and the plasma polymer coating appears to be excellent and remains strong after weathering.     

Enzymatic degradation of 3D scaffolds of starch-poly-(?-caprolactone) prepared by supercritical fluid technology

Starch-based polymers have been proposed for different tissue engineering applications due to their inherent properties. In this work, a polymeric blend of starch-poly-(?-caprolactone) (SPCL) was processed using supercritical fluid technology, namely, by supercritical assisted phase inversion. As SPCL is a biodegradable polymer, the matrices produced are susceptible of undergoing enzymatic degradation upon implantation in the human body. In vitro assessment of the enzymatic degradation of SPCL was carried out in different buffer solutions containing α-amylase and/or lipase. The effect of the presence of these enzymes was studied by monitoring different parameters in order to characterise both bulk and the surface of the scaffolds. As regards to bulk analysis, weight loss of the samples incubated for 1, 3, 7, 14 and 21 days was determined, further differential scanning calorimetry was carried out. The morphology of the scaffolds after these periods was analysed by micro-computed tomography (μ-CT) and surface chemistry was characterised by infra-red spectroscopy and contact angle measurements. Results suggest that SPLC scaffolds undergo bulk degradation, which is typically characterised by hydrolysis of chemical bonds in the polymer chain at the centre of the matrix, resulting in a highly porous material.     

Mechanical and Thermal Properties of Organic/Inorganic Hybrid Coatings

Two types of organic/inorganic hybrid coatings were produced by the sol-gel route from (a) 80% tetra-ethoxy-silane (TEOS) and 20% glycidoxypropyl-trimethoxy-silane (GPTMS) and (b) GPTMS with varying amounts of diethylene-triamine (DETA). Residual stress was measured from substrate curvature and modulus and hardness were studied using nano-indentation.Coatings derived from 80TEOS/20GPTMS are relatively stiff and brittle. Tensile residual stress, elastic modulus and hardness all increase as the curing temperature is increased to 350°C. The organic components are not cross-linked and act as network modifiers.Coatings derived from GPTMS/DETA are less stiff and softer. Increasing the DETA content increases both E and H by increasing the connectivity of the organic network which dominates the mechanical properties. Thermal degradation begins at about 250°C in all cases, but is retarded when the connectivity of the organic network is high.     

Weathering resistance of halogen-free flame retardance in thermoplastics

The influence of weathering on the fire retardancy of polymers is investigated by means of a cone calorimeter test, before and after artificial weathering. The surface degradation was monitored using different techniques (ATR-FTIR, microscopy, colour measurement). Different kinds of polymeric materials were chosen, all as they are used in practice: polycarbonate (PC) blends, polyamide (PA) and polypropylene (PP) flame-retarded with arylphosphate, melamine cyanurate (MC) and intumescent formulation based on ammonium polyphosphate (APP), respectively.All samples show material degradation at the surface due to weathering. No significant weathering influence occurs on the flame retardancy when it is a bulk property, as was observed for aryl phosphates in PC blends and MC in PA. When the fire retardancy is dominated by a surface mechanism, dependence on the duration of weathering is detected: for intumescent formulations based on ammonium APP in PP, a worsening in the formation of the intumescent network was observed.     

Au-nanoparticles grafted on plasma treated PE

Polyethylene (PE) surface was treated with Ar plasma. Activated surface was grafted from methanol solution of 1,2-ethanedithiol. Then the sample was immersed into freshly prepared colloid solution of Au-nanoparticles. Finally Au layer was sputtered on the samples. Properties of the modified PE were studied using various methods: AFM, EPR, RBS and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain (AFM) and creation of free radicals by EPR. After grafting with dithiol, the concentration of free radicals declines. The presence of Au and S in the surface layer after the coating with Au-nanoparticles was proved by RBS. Plasma treatment changes PE surface morphology and increases surface roughness, too. Another significant change in surface morphology and roughness was observed after deposition of Au-nanoparticles. Nanoindentation measurements show that the grafting with Au-nanoparticles increases adhesion of subsequently sputtered Au layer.     

Effect of boehmite nanorods on the properties of glycidoxypropyl-trimethoxysilane (GPTS) hybrid coatings

AlOOH boehmite nanorods, synthesized by a solid-based process, were incorporated into a sol–gel coating in which GPTS was used as a precursor. Transparent composite coatings with nanorod content up to 40 wt% were obtained by spin coating the sol–gel mixture on glass substrates. Nanorods in the coating were found be aligned parallel to the substrate surface. Mechanical properties, such as modulus and hardness of the nanorod filled coating, were slightly lower than coatings of the same composition but filled with commercially available nanosized boehmite particles. However, crack toughness was greatly improved, as supported by nanoindentation test results. The improvement in crack toughness was attributed to the high aspect ratio of the rigid nanorods, in addition to the fact that the nanorods were aligned within the composite parallel to the surface.     

Layer-by-layer polyelectrolyte coating of low molecular weight poly(lactic acid) nanoparticles

Low molecular weight (M(w)) poly(L-lactic acid) (PLA) nanoparticles were coated with polyelectrolytes (PEs) by layer-by-layer (LbL) technique using a filtration approach. Poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) were applied as PEs in coating. LbL coating is aimed to use in producing (nano)particulate drug delivery systems with improved biocompatibility and sustained or targeted release of drug substances. Nanoparticles of rapidly biodegradable polymers, like the low M(w) PLA, open up a possibility to control the release of the encapsulated substance by the coating, but set challenges to the coating process due to increased aggregation tendency and degradation rate of the polymer. When the core PLA nanoparticles were prepared by nanoprecipitation, surface properties of the nanoparticles were affected by solvent selection. Successful LbL coating of the PLA nanoparticles was obtained only with chloroform, but not with dichloromethane as the solvent during nanoprecipitation. Reason for this was found to be the more charged surface of the nanoparticles prepared with chloroform compared to the nanoparticles prepared with dichloromethane.     

纳米木质素/二氧化硅基微胶囊的制备及在自愈合涂层中的应用

利用磷酸化改性木质素/二氧化硅复合纳米颗粒(PAL/SiO₂)作为壁材包埋活性组分异佛尔酮二异氰酸酯(IPDI)制备微胶囊(PAL/SiO₂-IPDI). 通过加入少量反应活性更高的聚合多甲基多二异氰酸酯(PMDI), 与水反应形成聚脲, 以增加微胶囊的壁厚. 采用光学显微镜、 扫描电子显微镜(SEM)和激光粒度分析仪(DLS)研究了PAL/SiO₂复合纳米粒子掺杂量, 水油比和剪切速率对微胶囊表面形貌、 粒径和壁厚的影响. 结果表明, 所制备的微胶囊呈现规整球形, 壁厚为2.36~3.50 μm, 平均粒径为40.3~201.5 μm. IPDI作为芯材包埋在微胶囊中, 芯材含量约为82.8%. 将制备的PAL/SiO₂-IPDI微胶囊添加到环氧树脂中得到自愈合环氧树脂涂层. 其在高盐浓度溶液中的抗侵蚀测试结果显示, 添加质量分数4%的PAL/SiO₂-IPDI微胶囊的环氧树脂涂层在划破后能够快速愈合, 显著降低基底的腐蚀电流和腐蚀速率. 纳米压痕实验表明, 环氧涂层的硬度为249.99 MPa, 而添加PAL/SiO₂-IPDI微胶囊后硬度增加到302.98 MPa, 弹性模量也有提高.     

The nanomechanical behavior of a graphite nanoplatelet/polycarbonate nanocomposite

Quasi-static nanoindentation has been used to characterize the mechanical properties of polycarbonate reinforced with graphite nanoplatelets (GNPs). Poor dispersion or low quality interfacial interactions of GNPs in a polymer matrix can significantly decrease the relative improvement in the material's mechanical strength and stiffness. In this study, the surfaces of GNPs were modified to achieve better dispersion and interfacial interaction between fillers and matrix. The GNP/PC nanocomposite has a heterogeneous microstructure, and the original mechanical properties between filler and matrix have large differences. Using a spatially sensitive probe method leads to measured values of modulus and hardness that correlate with the indentation sampled volume. A grid indentation procedure was performed with variable sampling volumes to provide a statistical measurement of modulus and hardness for the nanocomposite materials. The surface treatment leads to a significant increase in both stiffness and hardness for GNP reinforced composites.