Carbon Nanotubes as Conductive Filler in Segregated Polymer Composites - Electrical Properties

Abstract

Carbon nanotubes are of great interest as a filler for polymer composites due to their unique properties such as high electrical and thermal conductivity, ultrahigh mechanical strength, high ratio length/diameter (1000) at nanosized value of diameter. Several recent reviews summarizing different aspects of the composite investigations display a broad spectrum of properties useful for production of sensitive electrodes, sensors for chemical vapours, electromagnetic radiation shielding materials, electrical heaters, as well as pressure, deformation and temperature sensors and photovoltaic cells (Thostenson et al., 2001; Popov, 2004; Breuer & Sundararaj, 2004; Ramirez, 2005; Moniruzzaman & Winey, 2006; Baibarac & Gomez-Romero, 2006; Rajesh et al., 2009; Spitalsky et al., 2010). More substantially the methods of preparation and properties of CNT based polymer composites are described in new book (Mittal, 2010). Specials interest is represented by electrical properties of the composites because of the variety of potential applications. Such systems are represented in a form of the polymer matrix containing conductive filler creating the conductive network. It seems promising to prepare composite materials with small conductive filler content, which preserves mechanical properties of a polymer along with high electrical conductivity. Random filler distribution typically shows the value of percolation threshold (i.e. critical filler concentration at which a conversion from nonconductive to conductive state occurs) within 10–30% for dispersed metals and 5-15 % for carbon black , for example (Foulger, 1999; Mamunya et al., 2002a). Selectively localized conductive particles in a polymer matrix can form the ordered network of conductive phase creating so-called segregated systems. Considerably lower value of percolation threshold c compared to usual filled polymers can be attained due to this effect, for example (Chan et al., 1997; Bouchet et al., 2000; Mamunya et al., 2002b). On the other hand, high ratio of carbon nanotubes causes lower value of percolation threshold compared to the isotropic filler particles (Simien et al., 2008). Combination of these two factors can lead to the existence of conductivity in the polymer composite at extremely low content of carbon nanotubes. Segregated polymer composites can be formed either by technological methods in the composites processed by hot compacting or in the polymer blends by filler localization inside one polymer component and on the interface. In this chapter the conditions of creation of the ordered distribution of conductive filler (namely carbon nanotubes) in