In the development of composite materials, the dimensions of reinforcements have decreased from macroscopic to nanoscopic in order to achieve the various advantages of nanoscale structures. Carbon nanotubes (CNTs) have high potential for improving the mechanical, thermal, and electrical properties of composite materials, which has inspired researchers to use them as reinforcements for metal and ceramic matrices, as well as polymer matrices. [1][2][3] In order to develop successful CNT-reinforced nanocomposites, the most important aspect is to transfer the extraordinary properties of CNTs to the matrix. Two main issues have to be faced to improve effectively the material properties of the nanocomposites by adding CNTs as fillers. One is the proper dispersion of the individual CNTs in the matrix and the other is the interfacial bonding between CNTs and the matrix. Homogeneous dispersion of CNTs is required to overcome the performance limit caused by agglomeration of CNTs in the matrix.[4-6] Nanoscale structures exhibit an enormous surface area several orders of magnitude larger than conventional macroscopic fillers. The increase of surface area enhances stress-transfer capabilities but is also responsible for the agglomeration of CNTs. Therefore, a new processing route should be investigated to achieve a high degree of dispersion in the matrix, a breakup of the agglomerates, and a good wetting with the matrix. Here, we report a novel layering approach for CNT/Cu laminated nanocomposites based on selective dip-coating of CNTs. Homogeneous distribution of CNTs within the plane can be easily obtained by dip-coating CNTs with a stable dispersive colloidal solution. Moreover, the porosity (or density of CNTs) and thickness of the CNT layer can be controlled by the density of the colloidal solution and the withdrawal velocity during dip-coating. Distribution along the out-of-plane direction can be automatically achieved by stacking the CNT layers. The mechanical properties of nanocomposites show great improvement caused by an enhanced load-sharing capacity of CNTs homogeneously distributed within the plane, as well as a bridging effect of CNTs along the out-of-plane direction between the upper and lower layers of the matrix. The layering approach is applicable to a wide range of functional materials, and here we demonstrate its potential use in reinforcing composite materials. Sandwich-type laminated nanocomposites were fabricated by stacking layers with CNTs and layers of electroplated Cu matrix (Fig. 1). The most important process in the development of laminated nanocomposites in this study was the preparation of a stable dispersive colloidal solution for a uniform dip-coating of CNTs. CNTs generally form aggregates owing to very strong van der Waals interactions. It is important to obtain stable dispersions of CNTs in water for applications in nanocomposites. [7] To prepare stable aqueous dispersions of CNTs, the repulsion forces should overcome the van der Waals forces between the CNTs and their zeta potentials. [7,8...
Micro-tensile properties of hard and soft thin films, TiN and Au, were evaluated by directly measuring tensile strain in film tension using the micro-ESPI(electronic Speckle Pattern Interferometry) technique. Micro-tensile stress-strain curves for these films were obtained and the properties were determined. TiN thin film 1 μm thick and Au films with two different thicknesses (t=0.5 μm and 1 μm) were deposited onto the silicon wafers, respectively, and micro-tensile specimens wide 50, 100 and 200 μm were fabricated using micromachining. In-situ measurement of the micro-tensile strain during tensile loading was carried out using the subsequent strain measurement algorithm and the ESPI system developed in this study. The micro-tensile curves showed that TiN thin film was a linear-elastic material showing no plastic deformation and Au thin film was an elastic-plastic material showing significant plastic flow. Effect of the specimen dimensions on mechanical properties was examined. It was revealed that tensile strengths for both films were slightly increased with increasing specimen width. Furthermore, variations of yielding strengths for the thin film Au with change of the dimension were investigated.
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