Optical properties of polymer nanocomposites

Nanomaterials have emerged as an area of interest motivated by potential applications of these materials in light emitting diodes, solar cells, polarizers, light-stable colour filters, optical sensors, optical data communication and optical data storage. Nanomaterials are of particular interest as they combine the properties of two or more different materials with the possibility of possessing novel mechanical, electronic or chemical behaviour. Understanding and tuning such effects could lead to hybrid devices based on these nanocomposites with improved optical properties. We have prepared polymer nanocomposites of well-defined compositions and studied the optical properties of powders and their thin films. UV-vis absorption spectroscopy on nanocomposite powders and spectroscopic ellipsometry measurements on thin films was used to study the effect of interfacial morphology, interparticle spacing and finite size effects on optical properties of nanocomposites. Systematic shift in the imaginary part of the dielectric function can be seen with variation in size and fraction of the gold nanoparticle. The thickness of the film also plays a significant role in the tunability of the optical spectra.     

A new tip area function for instrumented nanoindentation at extremely small contact depths

The accuracy of measurement of mechanical properties of a material using instrumented nanoindentation at extremely small penetration depths heavily relies on the determination of the contact area of the indenter. Our experiments have demonstrated that the conventional area function could lead to a significant error when the contact depth was below 40 nm, due to the singularity in the first derivation of the function in this region and thus, the resultant unreasonable sharp peak on the function curve. In this paper, we proposed a new area function that was used to calculate the contact area for the indentations where the contact depths varied from 10 to 40 nm. The experimental results have shown that the new area function has produced better results than the conventional function.     

Microstructure and Mechanical Properties of Nanocrystalline Tungsten Thin Films

Tungsten (W) thin films were prepared by magnetron sputtering onto Si (100) substrates. Their microstructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The hardness and modulus were evaluated by nanoindentation. It is found that a 30 nm Cr sticking layer induces structure changes of deposited W film from β-W to α-W structure. In addition, remarkable hardness enhancement both for the deposited and annealed W...     

Critical insights into the reinforcement potential of cellulose nanocrystals in polymer nanocomposites

Cellulose nanocrystals (CNCs) are highly polar, negatively-charged hydrophilic nanoparticles extracted from biomass through acid hydrolysis. They have high crystallinity and stiffness, as well as exceptional capability in reinforcing some polymer nanocomposites. While these remarkable improvements are limited to a certain class of polymers under strict conditions, CNCs can contribute to improving nanocomposite performance via other means, such as nucleating effect or cross-linking capacity. In this review, we offer critical insights into the reinforcing mechanism(s) of CNC-polymer nanocomposites and the factors that influence their performance. We aim to provide answers to the following questions: (1) how do CNCs contribute to nanocomposite reinforcement via percolation theory; (2) how to form a percolated CNC network in a CNC-polymer nanocomposite; (3) what are the factors affecting CNC performance and how do they work; and (4) how can we take advantage of CNC’s attributes to create high-performance nanocomposites?     

Nanoindentation mapping of mechanical properties of cement paste and natural rocks

This paper reports a study to assess nanoindentation mapping of mechanical properties of cement paste and natural rocks. Initial work seems to show that mechanical property mapping by nanoindentation is feasible and can be related to microscopic information. Further work is however required on the effect of indent size and spacing. Such a testing technique can be very useful for materials with different phases to study the intrinsic properties of each component, and also the interaction and properties of the interfacial regions of different phases. The values of Young's modulus and hardness of the individual mineral phases were also determined by statistically analysing a large number of experimental data.     

Nanoindentation of Ni-Ti Thin Films

Ni-Ti thin films of various compositions were sputtered-deposited on silicon substrates. Their mechanical properties (hardness and Young's modulus) were then determined using a nanoindenter equipped with a Berkovich tip. This paper examines the effects of composition on the mechanical properties (hardness and Young's modulus) of the sputter deposited Ni-Ti thin films. This is of particular interest since the actuation properties of these shape memory alloy films are compositionally sensitive. The surface-induced deformation is revealed via Atomic Force Microscopy (AFM) images of the indented surfaces. Which show evidence of material pile-up that increases with increasing load. The measured Young's moduli are also shown to provide qualitative measures of the extent of stress-induced phase transformation in small volumes of Ni-Ti films.     

Nanoindentation and microstructure analysis of resistance spot welded dual phase steel

A nanoindentation hardness study has been conducted on the tempered region and the base metal in a dual phase steel subjected to rapid thermal cycles of resistance spot welding. Nanohardness results revealed “softening” at nano-scale for tempered martensite when compared to martensite in the base metal. At the tempered region, the ferritic matrix presented a slight reduction in hardness while the tempered martensite seemed to have a major contribution to the measured softening at micro-scale.     

聚合物/粘土纳米复合材料研究进展

聚合物/粘土纳米复合材料(PCN)是近几年纳米材料领域中的研究热点.综述了聚合物/粘土纳米复合材料的几种制备方法及研究进展,并将纳米复合材料与普通材料的物理性能相比较,得知纳米复合材料有优良的物理性能.总结了这一领域尚待解决的问题.     

碳纳米管增强聚合物复合材料的研究进展

论述了碳纳米管/聚合物纳米复合材料的各种制备方法和最新进展。详细讨论了碳纳米管/聚合物纳米复合材料的结构和性能,并对今后的研究方向进行了展望。     

Extracting thin film hardness of extremely compliant films on stiff substrates

A previously reported method for extracting the thin film hardness from nanoindentation into a film on an elastically mismatched substrate was applied to four different cases of extreme mismatch in elastic properties: Parmax, Ultem, Polysulfone and Perfluorocyclobutyl polymer thin films on Si substrates. All of these cases represent extremely compliant films on a stiff substrate, where the ratio of film shear modulus to substrate shear modulus ranged from 0.008 to 0.036. Analyzing the nanoindentation data into these film/substrate systems poses a significant limitation when using the Oliver and Pharr method as the hardness increases rapidly with indentation depth. Therefore, a method involving the measured contact stiffnesses to more accurately determine the correct contact areas was used to extract the true hardness of the polymer thin films. The results indicate that our method is able to remove the substrate effects as well as the complications arising from pile-up and surface roughness to yield a wide plateau in hardness despite the extreme elastic mismatch conditions.     

Nanoindentation study of single-crystal NaTh2(PO4)3

The single crystals of sodium dithorium orthophosphate NaTh₂(PO₄)₃ (NThP) were studied by means of micro/nanoindentation. The NThP hardness was found to be Н_N = 8.76 ± 0.18 GPa and the elastic modulus Е_N = 144 ± 1 GPa. Microhardness anisotropy of the NThP crystal unequal faces is insignificant. The non-uniformity of plastic strain observed for the NThP is caused by fracture initiation and growth in the imprint. The average fracture toughness index (K_Ic) for the NThP is estimated to be equal to 0.56 MPa m^0.5.     

聚合物/MMT纳米复合材料的结晶性能

综述了尼龙/MMT、PP/MMT、PET/MMT等代表性的结晶性聚合物/MMT纳米复合材料结晶行为,分析了MMT的加入对聚合物结晶的影响,提出建立聚合物/MMT纳米复合材料宏观性能和微观结构之间的关系,并展望了未来的发展方向.     

Nanoindentation Measurements of the Mechanical Properties of Ni Thin Films: Effects of Film Microstructure and Substrate Modulus

This paper presents the results of nanoindentation measurements of the hardness and moduli of normally and obliquely deposited nanocrystalline Ni films on substrates of SiO₂, Si, and bulk Ni. Following an initial characterization of film microstructure and surface topography with atomic force microscopy (AFM), the paper examines the effects of film microstructure, film thickness, and substrate modulus on the measured film mechanical properties. Obliquely deposited films are shown to have lower hardness values than normally deposited films. The measured hardness values and material pile-up are also shown to depend significantly on the mismatch between the film modulus and substrate modulus. A framework is presented for quantifying the effects of substrate modulus mismatch on basic film mechanical properties.     

Synthesis and characterization of silver/thiophene nanocomposites by UV-irradiation method

Silver/thiophene (Ag/Th) nanocomposites have been prepared by UV-irradiation method. The resulting products were characterized by Elemental Analysis (EA), X-ray Photoelectron Spectroscopy (XPS), optical absorption spectroscopy, Fourier Transform Infrared (FT-IR), Thermal Gravimetric Analysis (TGA), X-ray Diffraction (XRD), transmission electron microscopy (TEM) and Scanning Electron Microscope (SEM). We prepared Ag/Th nanocomposites successfully for the first time without any reducing or binding agent. XRD patterns are consistent with that of silver and thiophene molecules are present in the final products. A SEM image shows the uniform particles distribution. The particles are spherical in nature and seem to be nanosized, typically in the range of < 100 nm. Finally, we observed a strong interaction between the Ag⁺ ion and sulfur atom of thiophene ring. This work provides a simple route for the synthesis of Ag/Th nanocomposites.     

聚合物/蒙脱土纳米复合材料的制备与结晶性能

本文综述了制备聚合物 /蒙脱土纳米复合材料的插层方法 ,并对有代表性的结晶性聚合物 /蒙脱土纳米复合材料的结晶性能进行了讨论。蒙脱土的加入对聚合物的结晶有两种作用 ,一方面是对聚合物有异相成核的作用 ,可以提高聚合物的结晶温度和结晶速率 ,降低结晶活化能 ;另一方面是对聚合物结晶生长有阻碍作用 ,导致结晶速率下降 ,结晶活化能提高     

Measuring mechanical properties of plasma-sprayed alumina coatings by nanoindentation technique

AISI 1020 steel substrate is coated with alumina as feedstock material using plasma spraying process in order to correlate the microstructural features with mechanical properties of coating. The present work focuses on the effects of microstructural inhomogeneity on mechanical properties of alumina coating through nanoindentation technique. Young’s modulus and hardness of the alumina coating are analytically evaluated. Indentation stress–strain curves are generated from the experimentally obtained load–displacement curves to characterise the mechanical properties of the coating. The results have shown large variation in hardness and Young’s modulus of alumina due to microstructural inhomogeneity of the coating.