We report formation of polyelectrolyte/multiwall carbon nanotube (MWNT) multilayers by the layer-by-layer assembly technique. Both "hollow" and "bamboo" type MWNTs were employed. Scanning electron and atomic force microscopy indicate high structural homogeneity of the prepared composites. Ellipsometry and the absorbance spectroscopy confirm sequential adsorption of oppositely charged nanotubes and the polyelectrolyte resulting in uniform growth of the polyelectrolyte/MWNT films. Measurements of the mechanical properties show that these are strong composite hybrid films with mechanical properties exceeding many carbon nanotube composites made by mixing, or in-situ polymerization. Bamboo-type carbon nanotube composites display ultimate tensile strength of 150 ± 35 MPa and Young modulus of 4.5 ± −0.8 GPa as compared to 110 ± 25 MPa and 2 ± 0.5 GPa in composites made from common hollow MWNTs. This indicates that the morphology of the fibers can substantially improve matrix connectivity on the material mitigating "telescopic effect" in MWNTs. The films made from bambootype MWNTs approach in strength recently reported layer-by layer composite films from single wall carbon nanotubes, while being substantially less expensive. These results confirm the potential of the layering method for the manufacturing of composites with high load of strong filler and importance of uniform distribution and good interconnectivity between carbon nanotubes and the polymer matrix.

A novel strategy for the fabrication of multiwall carbon nanotube-nanocrystal heterostructures is shown. Different quantum dots (QDs) with narrow size distributions were covalently coupled to carbon nanotubes (CNTs) and silica-coated CNTs in a simple, uniform, and controllable manner. The structural and optical properties of CNT/QD heterostructures are characterized by electron microscopy and photoluminescence spectroscopy. Complete quenching of the PL bands in both QD core and core/shell heterostructures was observed after adsorption to the CNTs, presumably through either carrier ionization or energy transfer. The deposition of a silica shell around the CNTs preserves the fluorescence properties by insulating the QD from the surface of the CNT.

The mechanical properties of polymer composites, reinforced with silica-coated multiwall carbon nanotubes (MWNTs), have been studied using the nanoindentation technique. The hardness and the Young's modulus have been found to increase strongly with the increasing content of these nanotubes in the polymer matrix. Similar experiments conducted on thin films containing MWNTs, but without a silica shell, revealed that the presence of these nanotubes does not affect the nanomechanical properties of the composites. While carbon nanotubes (CNTs) have a very high tensile strength due to the nanotube stiffness, composites fabricated with CNTs may exhibit inferior toughness. The silica shell on the surface of a nanotube enhances its stiffness and rigidity. Our composites, at 4 wt % of the silica-coated MWNTs, display a maximum hardness of 120 +/- 20 MPa, and a Young's modulus of 9 +/- 1 GPa. These are respectively 2 and 3 times higher than those for the polymeric matrix. Here, we describe a method for the silica coating of MWNTs. This is a simple and efficient technique, adaptable to large-scale production, and might lead to new advanced polymer based materials, with very high axial and bending strength.

A method based on the conventional lithographic technique combined with the layer-by-layer (LBL) assembly process is applied to the construction of free-standing micro- and nanostructured matrixes. The method enables controlled shaping and considerable chemical and mechanical stability of the self-assembled monolayers, allowing for high reproducibility in manufacturing. The matrixes are characterized by controlled geometry, surface topography, and chemical composition. The complete architecture is made up of successive layers of intercrossed carbon nanotubes that self-assemble into orderly structures. In particular, the present method aims to create architectures and topographies that mimic those occurring naturally (native tissue structures). In addition, nanoindentation and nanoscratch techniques were used to evaluate the mechanical properties of the carbon nanotube-based matrixes.

SUMMARYInsect cuticle is a highly adaptive material that fulfils a wide spectrum of different functions. Cuticle does not only build the exoskeleton with diverse moveable parts but is also an important component of a stunning variety of mechanosensory receptors. Therefore, the mechanical properties of these specialized cuticular systems are of crucial importance. We studied the different cuticular layers of the head part (gula) of the head-to-neck ball articulation of Pachnoda marginata and of the photomechanic infrared (IR) sensilla of Melanophila acuminata on the basis of cross sections. In our study, we combined histological methods (i.e. detection of the different types of cuticle by specific staining) with measurements of hardness (H) and reduced elastic modulus (E r ) by nanoindentation technique. In the gula of Pachnoda we found an unusual aberrance from the well-known layering. Between the epi-and exocuticle, two meso-and one endocuticular layers are deposited which are softer and more elastic than the underlying exo-and mesocuticular layers. The hardest of all examined materials is the cuticle of the exocuticular shell of the internal sphere of the Melanophila IR sensillum with H=0.53 GPa whereas the inner mesocuticular core of the sensillum represents the most elastic and softest layer with values of H=0.29 GPa and E r =4.8 GPa. Results are discussed with regard to the proposed functions.

We study the dielectric properties of nanocomposites in the 0–1.5-GHz frequency regime. These composites consist of electrically insulated metallic nanoparticles and carbon nanotubes, the elongated nanostructures in this study, uniformly dispersed in a dielectric matrix. We find that the properties of these composites depend crucially on the shape and monodispersity of the nanoparticles. While at high concentrations the spherical nanoparticles cause only slight modification of the dielectric function of the composite with respect to the matrix, the elongated nanoparticles produce composites with an enhanced real part of the dielectric function and low imaginary part. Our theory, which is in excellent agreement with these results, suggests specific ways to further improve the dielectric properties of the composites.

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We report on mechanical properties of multiwall carbon nanotubes (MWNTs)-polymer composites using the nanoindentation technique. The nanoindentation experiments conducted on thin films containing MWNTs revealed that the presence of nanotubes does not affect the nanomechanical properties of the composites. Even a layer-by-layer assembly of MWNTs with a high concentration and a homogeneous distribution of carbon nanotubes does not ensure reinforcement of the composites. For that reason, we synthesized and utilized carbon nanotubes with a silica shell. Nanohardness and Young's modulus have been found to increase strongly with increasing content of these nanotubes in the polymer matrix. The silica shell on the surface of a nanotube enhances its stiffness and rigidity. Our composites, at 4wt.% of the silica-coated MWNTs, display a maximum hardness of 12020MPa and a Young's modulus of 91GPa. These are, respectively, 2 and 3 times higher than those for the polymeric matrix.