Mechanical properties of multilayered chitosan/CNT nanocomposite films

A multi-performance MWCNT-reinforced chitosan nanocomposite was fabricated by two methods: a freeze-drying process associated with the sublimation and compression (SAC) method; and the casting-evaporation (CE) method. We obtained ordered and multilayered structures with limited porosity, and well-dispersed MWCNT structures of the chitosan nanocomposite, especially with the SAC method. In the case of the nanocomposite films prepared by the CE method, the mechanical strength and elongation were significantly increased by up to about 40% compared with the pure chitosan films. On the other hand, the ordered and porous multilayered pure chitosan films prepared by the SAC method showed significantly lower tensile strength and elongation compared to the pure solid chitosan films. However, the relative enhancement of the mechanical properties of multilayered MWCNT/chitosan nanocomposites with porosity was higher, especially in terms of the elongation, which showed a twofold improvement in strain. The relaxed bond, which could be a relatively strong hydrogen bond, between the functional groups in the chitosan chains and the functionalized surface of the MWCNTs might be stretched under stress, thereby improving the ductility of the multilayered nanocomposite films. In addition, the viscoplastic behavior of the films by the CE method could become more active with increasing strain rate. Interestingly, ordered and porous pure chitosan films did not reveal the viscoplastic behavior; it rather presented strain softening and viscoelastic characteristics. However, the interaction between the chitosan chains and the surface-modified MWCNTs could regenerate viscoplasticity of the chitosan films.     

Mechanical properties of gradient and multilayered TiAlSiN hard coatings

Multicomponent coatings based on different metallic and non-metallic elements possess the combined benefit of individual components leading to further improvement of coating properties. In this study, monolayered Ti-Al-N, multilayered Ti-Al-N/TiN, gradient Ti-Al-Si-N, and multilayered Ti-Al-Si-N/TiN coatings were synthesized by using a cathodic-arc evaporation (CAE) system. In addition to Ti, Ti₃₃Al₆₇ and Al₈₈Si₁₂ cathodes were used for the deposition of Ti-Al-N, and Ti-Al-Si-N coatings, respectively. The gradient Ti_0.50Al_0.43Si_0.07N, and multilayered Ti_0.50Al_0.43Si_0.07N/TiN with nanograins separated by disordered grain boundaries possessed lower residual stress (− 2.8 ~ − 4.8 GPa) than that of monolayered Ti-Al-N (− 6.8 GPa) and multilayered Ti-Al-N/TiN coatings (− 5.7 GPa). The highest hardness was obtained for the gradient Ti_0.50Al_0.43Si_0.07N (38 ± 2 GPa) with Ti/(Ti + Al + Si) content ratio being 0.5. On the contrary, the multilayered Ti_0.50Al_0.43Si_0.07N/TiN possessed the highest H³/E^?2 ratio of 0.182 ± 0.003 GPa, indicating the best resistance to plastic deformation, among the studied coatings.     

Mechanical properties of nanocomposite thin films

The mechanical properties of nanocomposite thin films are reviewed. Two types of films are considered: artificially multilayered thin films and granular metal thin films. Artificially multilayered thin films, which are composed of alternating layers of two different materials, can display variations (reductions or enhancements) of the order of 15 to 30% in their elastic behavior as the bilayer repeat length is reduced below about 5 nm. Significant enhancements in the hardness of these materials are also observed for this range of bilayer repeat length. Granular metal films, which are composed of a thin film ceramic matrix embedded with metal granules of diameters as small as a few nanometers, display novel behavior in their hardness and apparent elastic behavior as measured by low-load indentation methods. This appears to be correlated with the percolation threshold of the metal.     

Mechanical properties of diamond thin films

Abstract

The mechanical properties of diamond films deposited via hot filament chemical vapour deposition have been determined using a range of techniques, and related to the composition and morphology of the diamond films as determined by laser Raman spectroscopy. As the quality of the film increases, its hardness (as determined by the volume law of mixtures hardness model) also increases until it is larger than values often reported for polycrystalline bulk material, a consequence of the very small grain size in the films. Coating adhesion, as determined from indentation adhesion tests, also appears to improve with coating quality. Variations in the behaviour of the friction coefficient between diamond films and diamond and steel counterfaces are less well defined, but it appears that the surface morphology of the film is important in dictating the behaviour rather than the quality of the diamond. These results are discussed in the context of the potential use of diamond coatings in tribological applications.

MST/1695     

Mechanical properties of nanocomposite organosilicate films

Nanocomposite coatings have been deposited on plastic substrates by the dipping–drawing technique. The coatings were constituted by a matrice of a hybrid organomineral gel and a reinforcement made of amorphous silica. Two methods by which increase the silica content were investigated: silica was added via a silicon alkoxide compound or via dense silica particles of 10 nm size. Young's modulus and the hardness of the coating were measured using home-built equipment, and results compared to literature models. It is shown that the agreement between models and experimental values depends on the method of preparation of the nanocomposite coating. On the other hand, deviations appear when the volume fraction of reinforcement surpasses the three-dimensional percolation threshold.     

具有多层结构的聚合物复合薄膜的介电和磁性能

采用旋涂法制备了 Fe3 O4/聚偏氟乙烯(PVDF)复合薄膜(A)、多壁碳纳米管(MWCNT)/PVDF复合薄膜(B)以及纯PVDF薄膜(P)。利用热压法制备具有3层结构的AAA、ABA及APA 复合薄膜。为了探究层状结构对复合薄膜介电和磁性能的影响,制备了单层膜A作为对比(厚度与AAA复合薄膜相同)。分别研究了薄膜的介电和磁性能。结果表明：由于界面效应,同等厚度的AAA复合薄膜较A膜而言具有较高的介电常数;以B和P薄膜替代AAA结构中间层薄膜后,其中ABA复合薄膜的介电常数高于AAA及APA复合薄膜,同时保持较低的介电损耗。对于磁性能,层状结构对复合薄膜的饱和磁化强度及矫顽力均无明显的影响,而ABA复合薄膜的饱和磁化强度高于AAA及APA复合薄膜,且ABA和APA复合薄膜的矫顽力增加。层状结构设计不仅能够调节复合材料的介电性能和磁性能,而且有利于不同纳米填料的分散,为制备多功能聚合物复合材料提供了一定的借鉴作用。     

Mechanical properties of metal and compound films

Experimental results on internal stress, Young's modulus and adhesion of metal and compound films are presented and the correlation between these quantities is discussed. Internal stress and Young's modulus were determined by simultaneous in situ measurements during film deposition. In addition to the internal stress values of metal films, which have been given by many workers, we include results on compound films, some of which showed compressive stresses. The Young's moduli of films of such compounds as MgF₂ and TiC and of carbon, which have not previously been established, were determined. The strain energy density accumulated in a film during deposition was evaluated from the measured values of Young's modulus and internal stress. In some films, cracks or wrinkles were generated by strain energy, leading to the spontaneous peeling of the films from the substrates. The adhesion experiments were performed using the topple and pull test. The adhesive forces were directly measured and the adhesion energies were estimated. The effect of the substrate temperature and ion bombardment on the adhesion were investigated. The values of adhesion energies were compared with strain energies and the meaning of the adhesion test was considered.     

Electrical properties of multilayered Al/Ni and Al/Mo films

The structural and electrical properties of multilayered metallic systems prepared by r.f. sputtering are reported. The multilayers consist of alternating layers of aluminium and molybdenum or nickel, with superlattice periodicities in the range of 1.5–9.0 nm. The resistivity and its temperature dependence were measured at temperatures between 170 and 320 K. The most striking feature is the change in sign of the temperature coefficient of resistivity as the thickness of the aluminium layer is varied. The experimental results are interpreted in terms of a grain boundary reflection model.     

Coupling in multilayered magnetic films

A coupling between the magnetization of two ferromagnetic films separated by a thin metallic layer has been observed. It is shown that when the intermediate layer is palladium the coupling results from diffusion of magnetic atoms into the palladium which makes it weakly ferromagnetic. The main systems in which ferro-antiferromagnetic coupling is observed are Co-CoO, Ni-NiO, FeNi-FeNiMn. In the latter case domain patterns and ripple are observed by electron microscopy.     

Mechanical characterization of LiPON films using nanoindentation

Nanoindentation has been used to characterize the elastic modulus and hardness of LiPON films ranging in thickness from 1 to 10 μm. Four fully dense, amorphous films were deposited on glass and sapphire substrates with one film annealed at 200 °C for 20 min. The modulus of LiPON is found to be approximately 77 GPa, and argued to be independent of the substrate type, film thickness, and annealing. Based on the numerical analysis of Monroe and Newman, this value may be sufficiently high to mechanically suppress dendrite formation at the lithium/LiPON interface in thin film batteries [1]. Using Sneddon's stiffness equation and assuming the modulus is 77 GPa, the hardness is found to be approximately 3.9 GPa for all but the annealed film. The hardness of the annealed film is approximately 5% higher, at 4.1 GPa. Atomic force microscopy images of the residual hardness impressions confirm the unexpected increase in hardness of the annealed film. Surprisingly, the indentation data also reveal time-dependent behavior in all four films. This indicates that creep may also play a significant role in determining how LiPON responds to complex loading conditions and could be important in relieving stresses as they develop during service.     

High-frequency ferromagnetic properties of multilayered FeCoHfO/AlOx films

For mobile communication, the ferromagnetic resonance frequency of magnetic films must be over 3 GHz. A suitable anisotropic field and high resistivity for high frequency applications were obtained by inserting insulator (AlO_x) layers into ferromagnetic layers (FeCoHfO). With this optimum configuration of three layers structure [FeCoHfO (400 nm)/AlO_x (10 nm)]₃, high frequency characteristics (permeability ∼ 100 at 100 MHz and ferromagnetic resonance frequency over 3 GHz) and high resistivity (ρ ∼ 1088) μΩ cm were achieved.     

Mechanical properties of amorphous and microcrystalline silicon films

Hydrogen-free amorphous silicon (a-Si) films with thickness of 4.5-6.5 μm were prepared by magnetron sputtering of pure silicon. Mechanical properties (hardness, intrinsic stress, elastic modulus), and film structure (Raman spectra, electron diffraction) were investigated in dependence on the substrate bias and temperature. The increasing negative substrate bias or Ar pressure results in simultaneous reducing compressive stress, the film hardness and elastic modulus. Vacuum annealing or deposition of a-Si films at temperatures up to 600 °C saving amorphous character of the films, results in reducing compressive stress and increasing the hardness and elastic modulus. The latter value was always lower than that for monocrystalline Si(111). The crystalline structure (c-Si) starts to be formed at deposition temperature of ∼ 700 °C. The hardness and elastic modulus of c-Si films were very close to monocrystalline Si(111). Phase transformations observed in the samples at indentation depend not only on the load and loading rate but also on the initial phase of silicon. However, the film hardness is not too sensitive to the presence of phase transformations.     

小麦醇溶蛋白膜力学性能与吸湿性研究

采用小麦醇溶蛋白的乙醇/水(70/30(v/v))溶液制备了醇溶蛋白膜,分析了交联剂用量与pH值对膜的拉伸性能、吸水性及透湿性的影响.结果表明,适度交联的醇溶蛋白膜具有最大拉伸强度与较高的断裂伸长率.随交联剂用量增加,膜的吸水率稍有下降,而透湿性显著增大.酸碱处理能显著提高膜的拉伸强度,但使吸水性稍有增大.