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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A fine tuning of the electrical conductivity from insulator to conductor behavior has been obtained for a multiwalled carbon nanotubes epoxy composite at a fixed substatistical percolation threshold content by varying the organization of the nanotubes network. A multiscale characterization has been carried out by transmission optical microscopy technique and small angle x-ray analysis that revealed a two level structure characterized by different topological arrangements for the micron sized clusters and nanosized isolated bundles, respectively. A picture of the multidimensional organization of the nanotubes network has been proposed to account for the observed transition modulation.