The document discusses carbon nanotube (CNT)/epoxy matrix nanocomposites. It notes that dispersing CNTs homogeneously in the epoxy matrix is important to exploit their potential but is difficult due to aggregation. Methods to improve dispersion include using surfactants or functionalizing CNTs. Functionalization can degrade CNT properties so alternative methods are sought. The properties of CNT/epoxy nanocomposites depend on the degree of CNT dispersion, with higher conductivity achieved above the percolation threshold.

1. CARBON NANOTUBES/EPOXY MATRIX NANOCOMPOSITE SYSTEMS METE 715 POLYMER NANOCOMPOSITES M.S. Ümit TAYFUN POLYMER SCIENCE & TECHNOLOGY

3. It is crucial to disperse them homogeneously in the matrix to exploit the potential of CNT. This is difficult to achieve since CNT tend to aggregate because of attractive van der Waals interactions. To improve dispersion of CNT in an epoxy matrix, Surfactants, for example polyoxyethylene-8-lauryl, have been used to disperse CNT before their introduction into a polymer matrix. The extraordinary mechanical (and electronic) properties of CNT depend on their specific chemical structure, and covalent functionalisation ntroduces defects and degrades the nanotube properties. This leads people to search for alternative ways to disperse CNT and to improve their bonding into polymer matrices.

5. Dispersion In addition to the size effect of fillers, the physical nature of particles also plays an important role in dispersing them into polymer matrix. It has been proved that these bundles and agglomerates result in diminished mechanical and electrical properties of composites as compared with theoretical predictions related to individual CNTs. P.-C. Ma et al. / Composites: Part A 41 (2010) 1345–1367

6. Ultrasonication: shock waves promotes the ‘‘peeling off” of individual nanoparticles located at the outer part of the nanoparticle bundles, or agglomerates, and thus results in the separation of individualized nanoparticles from the bundles Calendering process: the gap width between the rollers can be mechanically adjusted, thus it is easy to get a controllable and narrow size distribution of particles in viscous materials to achieve the desired level of particle dispersion Dispersion Techniques

7. Calendering may not be applied for dispersing CNTs into thermoplastic matrices, such as polyethylene, polypropylene and polystyrene. In contrast, CNTs can be conveniently dispersed into the liquid monomer or oligomer of thermosetting matrices, and nanocomposites can be obtained via the in situ polymerization. The minimum gap between the rollers is about 1–5 lm, which is comparable to the length of CNTs, but is much larger than the diameter of individual CNTs. These dimensional disparities between the roller gap and the CNT dimensions may suggest that calendaring can better disperse the large agglomerated CNTs into small ones at sub-micron level, although some individual CNTs may be disentangled out from the agglomerates P.-C. Ma et al. / Composites: Part A 41 (2010) 1345–1367

8. Ball milling: grinding method used to grind materials into extremely fine powder for use in paints Stir and extrusion: MWCNTs can be dispersed more easily than SWCNTs by employing stir. Extrusion is particularly useful to produce CNT/polymer nanocomposites with a high filler content Dispersion Techniques

9. Epoxy/CNT Nanocomposites

13. Adding a small quantity of a commercial block copolymer considerably enhances the mechanical properties of CNT–epoxy (CE) composites compared to the pure epoxy resin Q. Li et al.: Carbon nanotube/epoxy resin composites using a block copolymer as a dispersing agent, phys. stat. sol. (a) 201 , No. 13, R89– R91 (2004)

14. Functionalization of CNTs Functionalization of CNTs

15. Functionalization of CNTs Functionalization of CNTs M. Abdalla et al. / Polymer 48 (2007) 5662e5670 the increase in the relative intensity of the D-band can be taken as a crude measure of the degree of functionalization. Carboxylic acid functional groups were identified on the surface of the oxidized MWCNTs by FT-IR Spectroscopy.

16. The presence of CNT in the epoxy matrix increased the Tg of nanocomposite due to the difference in the extent of cross-linking reactions of epoxy. Functionalization of CNTs Functionalization of CNTs Effects of Silane Functionalization on the Properties of CNT/Epoxy Nanocomposites, Peng Cheng MA at Al, Adv. Funct. Mater, 2008

17. Pristine, carboxylic and ester functionalized (MWCNT)/poly(vinylidene fluoride)(PVDF)composites Functionalization of CNTs Functionalization of CNTs Large dielectric constant of the chemically functionalized carbon nanotube/polymer composites, Q. Li et al. / Composites Science and Technology 68 (2008) 2290–2296 In Fig. a and d, the length of the carboxylic functionalized MWCNTs is obviously shorter than that of pristine MWCNTs. The Fig. b and e shows that the amorphous carbon materials in carboxylic functionalized MWCNTs are less than that in pristine MWCNTs. In Fig. c and f, the catalysts embedded in the tip of MWCNTs had been removed. The closed tube tip was opened and the wall structure of the tubes was not damaged by acid treatment.

18. Electrical Conductivity of Epoxy/CNT Nanocomposites Mechanical and electrical properties of carbon nanotube reinforced epoxide resin composites, LIANG Shu-quan, et al/Trans. Nonferrous Met. Soc. China 17(2007) With increasing addition of carbon nanotubes, the resistivity of the composite decreases dramatically. This means the conductivity of the composite increase greatly. According to the percolation theory, when the content of carbon nanotubes is low, the carbon nanotubes distribute randomly in the matrix, and do not form a conductive network. With increasing content of carbon nanotubes, they begin to connect and interact with each other to form a network. The above percolation threshold values, the continuous conductive channel is developed in the frame of the network, the resistivity will decrease greatly. The matrix will change from insulator to semiconductor. The percolation threshold values for electrical characteristic transformation are 0.3% and 1.1%, respectively.

19. Effects of Silane Functionalization on the Properties of CNT/Epoxy Nanocomposites, Peng Cheng MA at Al, Adv. Funct. Mater, 2008 The electrical conductivity of nanocomposites containing silane-CNT decreased due to the wrapping of non-conductive silane onto CNT surface and well-dispersed CNTs. Electrical Conductivity of Epoxy/CNT Nanocomposites

20. Improvement in electrical, thermal and mechanical properties of epoxy by filling carbon nanotube, Zhou et al. – eXPRESS Polymer Letters Vol.2, No.1 (2008) 40–48 Generally, the percolation threshold is considered to be lower for fiber-shaped fillers (high aspect ratio) than for spherical particles. The percolation threshold has been determined to be below 0.1 wt%. However, once CNT loading is higher that 0.2%, resistivity decreased with CNT content slowly. Electrical Conductivity of Epoxy/CNT Nanocomposites

21. Improvement in electrical, thermal and mechanical properties of epoxy by filling carbon nanotube, Zhou et al. – eXPRESS Polymer Letters Vol.2, No.1 (2008) 40–48 I mpedance of the sample decreases significantly with frequency at frequencies higher than 100 kHz, indicating that at high frequency the impedance of the sample is dominated by the capacitance of the epoxy matrix. Therefore, it is possible to determine the connectivity between the CNT and polymer matrix by using the complex resistivity of the sample at different frequencies over a broad frequency range. Electrical Conductivity of Epoxy/CNT Nanocomposites Effect of frequency on resistivity of nanophased epoxy