The study of nanotubes has advanced tremendously in a relatively short time since its initial discovery in 1991 by Iijima. Owing to their exceptional morphological, electrical, thermal and mechanical characteristics, carbon nanotubes yield a material particularly promising as reinforcement in the composite materials with metallic matrixes, ceramics and polymers. The key factor in preparing a good composite rests on good dispersion of the nanotubes, the control of the bonding between nanotubes and matrix and the density of the composite material. Besides the type of nanotubes (SWNT, MWNT) the synthesis modes (arc discharge, laser, CVD) are important variables since they determine the perfection of the structure and the reactivity of the surface. Due to the unique properties of carbon nanotubes they are being widely studied as a constituent of composite material.

Excerpted from: Journal of Experimental Nanoscience International, multidisciplinary, the Journal of Experimental Nanoscience provides a showcase for advances in the experimental sciences underlying nanotechnology and nanomaterials.

Value from CNT Composites
CNT based composite materials are increasingly being considered for mechanical, electrical and space applications. Even studies on biosensor composites based on functionalized nanotubes and nanoparticles are reported

They are also being studied for their suitability and application in aerospace and aeronautical fields. A prospective application in aerospace that is being widely studied, including our work reported here, is the improvement of electrical properties of composites made from carbon nanotubes and epoxy resin.

To start with it was decided to mix the epoxy resin with graphite. The purpose was to make a light, thin and mechanically strong composite material to cover electric circuits against external electromagnetic interference, this is very important for air- and space-craft.

The epoxy resin that was used is a commercial Shell product Epon 828. Two types of curing agent were used along with the resin; mainly A1 curing agent and PAP8 agent. Also some of the resinþcuring agent samples were mixed with 20wt% of graphite and these were used for the analysis of the electrical resistivity studies.

[We stress that the first curing agent possesses polar groups in its chemical composition, whereas the second agent contains benzene groups. As a consequence, the mechanical properties of composites where the PAP8 agent has been used turn out to be improved. However, the stability of the mechanical properties, under varying pressure conditions, as well as the corresponding resistivity behavior, has not been investigated yet. In the present work we partially fill the gap concerning the electrical transport properties.]

CNT Resistivity Experiments
Comparing figures 11 and 12, which show plots for 0.5 wt%, it can be seen that the difference in the resistivity between the addition of CNTs and graphite amounts to six orders of magnitude. As it can be seen, an increase of wt% from 0.1 to 0.5 of graphite only decreases the resistivity by a few times, whereas, in the case of CNTs, an increase of 0.1 to 0.5wt% decreases the resistivity by three orders of magnitude.  The resistivity value changes drastically with the addition of a small quantity of CNTs.

We carried out a systematic study of the electrical properties of polymeric composite materials based on CNTs. The composite is obtained using the A1 curing agent, selected for the stability of the corresponding composite over a wide range of pressure values, in comparison with a different curing agent (namely PAP8). Benchmarking the resistivity properties of composites based on CNTs with those containing micron-sized graphite particles as a constituent, shows the advantages of using CNTs.

The change in the resistivity values for CNT-based composites turns out to be significant, even for small changes in the added CNT percentage. These results might be important for determining the most suitable ‘‘recipe’’ for the realization of composite materials for high-fidelity circuits in aerospace applications, or even in devices exposed to disturbances predominantly electromagnetic in their nature.

It is observed that the resistivity change is very large – near to three orders of magnitude when 20% graphite is added to the resinþA1 curing agent, whereas for the PAP8 curing agent the increase in resistivity due to addition of graphite is comparatively only marginal, of about three to five times. 

In the future it is planned to study CNT based composites with PAP8. Also, we plan to study the composite behavior in controlled humidity environments and for different temperatures.

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