Composite interfaces, nanotubes

Garcia EJ, Wardle BL, Hart AJ. Joining prepreg composite interfaces with aligned carbon nanotubes. Composites Part A Applied Science and Manufacturing. 2008 39(6) 1065-70. 

Li and Chou [73,74] have reported a multiscale modeling of the compressive behavior of CNT/polymer composites. The nanotube is modeled at the atomistic scale, and the matrix deformation is analyzed by the continuum FEM. The nanotube arrd polymer matrix are assttmed to be bonded by vdW interactions at the interface. The stress distributiorrs at the nanotube/polymer interface under isostrain and isostress loading conditiorrs have been examined. They have used beam elements for SWCNT using molectrlar structural mechanics, truss rod for vdW links and cubic elements for matrix. The rule of mixtrrre was used as for comparision in this research. The buckling forces of nanotube/polymer composites for different nanotube lengths and diameters are computed. The results indicate that continuous nanotubes can most effectively enhance the composite buckling resistance. 

C. Velasco-Santos, A.L. Martinez-Hernandez, and V.M. Castano, Carbon nanotube-polymer nano composites The role of interfaces. Composite Interfaces, 11 (8-9), 567-586, 2005. 

Potschke P, Bhattacharyya AR, Janke A, Goering H (2003) Melt mixing of polycarbonate/ multi-wall carbon nanotube composites. Composite Interfaces 10 389-404... 

There is currently considerable interest in processing polymeric composite materials filled with nanosized rigid particles. This class of material called "nanocomposites" describes two-phase materials where one of the phases has at least one dimension lower than 100 nm [13]. Because the building blocks of nanocomposites are of nanoscale, they have an enormous interface area. Due to this there are a lot of interfaces between two intermixed phases compared to usual microcomposites. In addition to this, the mean distance between the particles is also smaller due to their small size which favors filler-filler interactions [14]. Nanomaterials not only include metallic, bimetallic and metal oxide but also polymeric nanoparticles as well as advanced materials like carbon nanotubes and dendrimers. However considering environmetal hazards, research has been focused on various means which form the basis of green nanotechnology. 

G. Wang, J.J. Xu, and H.Y. Chen, Interfacing cytochrome c to electrodes with a DNA-carbon nanotube composite film. Electrochem. Commun. 4, 506-509 (2002). 

Qian H, Bismarck A, Greenhalgh ES, Shaffer MSP. Carbon nanotube grafted silica fibers Characterising the interface at the single fiber level. Composites Science and Technology. 

Nanocarbon hybrids have recently been introduced as a new class of multifunctional composite materials [18]. In these hybrids, the nanocarbon is coated by a polymer or by the inorganic material in the form of a thin amorphous, polycrystalline or single-crystalline film. The close proximity and similar size domain/volume fraction of the two phases within a nanocarbon hybrid introduce the interface as a powerful new parameter. Interfacial processes such as charge and energy transfer create synergistic effects that improve the properties of the individual components and even create new properties [19]. We recently developed a simple dry wrapping method to fabricate a special class of nanocarbon hybrid, W03 /carbon nanotube (CNT) coaxial cable structure (Fig. 17.2), in which W03 layers act as an electrochromic component while aligned... 

Eitan, A., Jiang, K. Y., Dukes, D., Andrews, R., and Schadler, L. S. 2003. Surface modification of mul-tiwalled carbon nanotubes Toward the tailoring of the interface in polymer composites. Chemistry of Materials 15 3198-201. 

Despite the results presented above, near-field microscopy has not been extensively used to characterize polymer/nanotube composites However, it can be noticed that AFM is a useful technique to locally probe the mechanical properties of the composites (at the polymer-nanotube interface for example). One possible reason for the small amount of studies by AFM and STM could be that observing the surface only does not permit to obtain much information on the nanotube dispersion state. For that kind of characterization, transmission electron microscopy is a key technique owing to the small nanotube diameter. 

The dispersion of carbon nanotubes in PU matrix can also be affected by the synthetic methods as well as the tensile stress etc. Xiong et al. found that the CNTs in the composites after tensile testing could easily take an ordered orientation along with the tensile direction on the cross-section perpendicular to the pressure direction, whereas the arrangement of the CNTs has not almost changed on the cross-section parallel to the pressure direction (62). The phenomenon that the SWNTs near the film substrate interface are driven to self-organize to a more ordered structure was discovered by Chen et al. (16). 

Keywords carbon nanotubes, PMMA, dispersion, interface, composites, strength, electrical conductivity, EMI shielding. 

As-synthesized MWCNT and SWCNT exist as bundles or ropes and tend to agglomerate due to strong van der Waals forces (13) (Figure 7.1). Unless the CNTs are separated in to individual tubes and dispersed in the polymer matrix, the interactions of the nanotubes with the polymer will be weak. The mechanical failure of such composites will occur due to slippage of the tubes in the bundle that are not bonded to the matrix. In addition, the aggregates or bundles reduce the aspect ratio of the reinforcement which affects electrical properties as well (15). Because of these factors the first step will be to open up these bundles to separate individual tubes by using different techniques to increase the volume of interface between the CNT and the matrix (40). 

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