In this work, the numerical and experimental investigation of the cladding modes re-organization in high refractive index (HRI) coated Long Period Gratings (LPGs) is reported. Moreover, the effects of the cladding modes re-organization on the sensitivity to the surrounding medium refractive index (SRI) have been outlined. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the SRI. In particular, if layer parameters are properly chosen, the transition of the lowest order cladding mode into an overlay mode occurs. As a consequence, a cladding modes re-organization can be observed leading to relevant improvements in the SRI sensitivity in terms of wavelength shift and amplitude variations of the LPGs attenuation bands.

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Please cite this article as: Martone, A., Faiella, G., Antonucci, V., Giordano, M., Zarrelli, M., The effect of the aspect ratio of carbon nanotubes on their effective reinforcement modulus in an epoxy matrix, Composites Science and Technology (2011), doi: 10.1016/j.compscitech.2011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe potentiality of carbon nanotubes as reinforcement material is not only due to their exceptional high modulus, but also to their high aspect ratio. Indeed, the nanotubes contribution to the mechanical reinforcement in a polymer is strongly dependent on their distribution within the hosting matrix. In fact, the clustering of carbon nanotubes does limit the theoretical enhancement of the composite mechanical properties by a reduction of their effective aspect ratio.In this work, the reinforcement efficiency of carbon nanotubes having different aspect ratios has been experimentally investigated at low filler contents in an epoxy system.From a theoretical point of view, the classical theory (Cox, 1952) concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube Random Contact Model (Philipse, 1996) which explicitly accounts for the progressive reduction of the tubes effective aspect ratio as the filler content increases. The validity of the proposed model was assessed by a comparison

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Carbon nanotube coated acoustic and optical sensors have been successfully studied for volatile organic compound (VOC) sensing applications, at room temperature. Here, Langmuir-Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been transferred onto different transducing sensors by using a linker-buffer LB multilayered material of cadmium arachidate pre-deposited on the sensor surface to promote adhesion of SWCNTs. Two different kinds of sensors have been designed, fabricated and utilized: quartz crystal microbalance 10 MHz AT-cut quartz resonators and standard silica optical fibre sensors based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in gas sensing applications: mass and refractive index, and their changes induced by gas molecule absorption. The results indicate high sensitivity, good repeatability and reversibility. Signals from each sensor type have been analysed and processed by using pattern recognition techniques such as principal component analysis and use of artificial neural networks. The recognition of the hybrid system is successfully performed, improving the data fusion from acoustic and optical sensors with SWCNT-functionalized sensors that are highly discriminating. To our knowledge, this is the first reported study of combined hybrid integration of acoustic sensors with optical fibre sensors using nanostructured materials as single-walled carbon nanotubes for VOC detection, at room temperature.