Nanocomposite conductivity

Let us briefly consider the conducting properties of hybrid nanocomposites. Conducting properties are manifested only with particular inorganic component to polymer ratios in which cmrent-conducting channels of fractal metal-containing clusters are formed in a polymeric matrix for one reason or other. The highest conductivity is achieved when the composite is converted into a network of interrelated current-conducting chains. This is where a percolation structure is achieved. To put it differently, critical concentrations of the filler (p (the percolation threshold) exist above which (9 > 9 ) the conductivity sharply increases. 

The author together with V. Sukharev has shown [21] that the percolation behavior of nanocomposites conductivity is different from the one typical for composites containing larger particles (Fig. 4). It has been demonstrated that the threshold filler concentration values are lower for nanocomposites than for composites with micron-size particles, and the slope of the curve in the... 

The percolation-like behavior of polymer-nanocomposites conductivity is a crucial property for device manufacture since all the electrophysical and a number of other properties change completely once the percolation threshold concentration is reached. The question should always be asked whether to utilize the properties of non-contacting nanoparticles in a polymer matrix below the threshold or those consisting of an interconnected particle network, with topology, connectivity and persistence length changing depending on the filler concentration excess over the percolation threshold value. 

Fig. 24. Dependence of the relative change of nanocomposites conductivity on relative humidity for nanocomposites with filler size ca.l2nm and different concentrations 1 7 vol %, 2 11 vol %, 3 17.5 vol %, 4 22 vol %...

Fig. 19. The simulated dependnece of CuS-PVA nanocomposite conductivity rdative diange on CuS content in composition [64]...

Keywords Conducting polymer Nanocomposites Conductive network Electrical properties... 

Ram et al. [53] studied CO gas sensing from ultrathin nanocomposite conducting polymer film. They have prepared PANI-Sn02 and PANI-TiOa nanocomposite films deposited on sulfonated polystyrene (PSS)-treated glass plate. Figure 17 shows the schematic of nanocomposite deposition of PANI-Sn02 and PANI-Ti02 films. 

The impact of aspect ratio and alignment of the carbon nanotubes on the nanocomposite conductivity has been studied recently (both experimentally and computationally) by Winey and coworkers [165-167]. In particular, Du et td. [165] demonstrated that in a poly(methyl methacrylate) (PMMA)/single wall carbon nanotube (SWCNT) nanocomposite, conductivity increases as a function of the SWCNT loading as predicted by Eq. (7.10), with a power-law exponent of 2.3 and percolation threshold of 0.39 wt%. Interestingly, the rapid increase in conductivity was accompanied by a rapid increase in the storage modulus, G (Figure 7.17). In fact,... 

Noble metal nanoparticles dispersed in insulating matrices have attracted the interest of many researchers fromboth applied and theoretical points of view [34]. The incorporation of metallic nanoparticles into easily processable polymer matrices offers a pathway for better exploitation of their characteristic optical, electronic and catalytic properties. On the other hand, the host polymers can influence the growth and spatial arrangement of the nanoparticles during the in situ synthesis, which makes them convenient templates for the preparation of nanoparticles of different morphologies. Furthermore, by selecting the polymer with certain favorable properties such as biocompatibiHty [35], conductivity [36] or photoluminescence [37], it is possible to obtain the nanocomposite materials for various technological purposes. 

There are several reports of Ag nanocomposites with conducting polymers like polyaniline [38] and polypyrrole [39]. However, electrical conducting properties of green metal - starch... 

Electrical conductivity measurements revealed that ionic conductivity of Ag-starch nanocomposites increased as a function of temperature (Fig.l7) which is an indication of a thermally activated conduction mechanism [40]. This behavior is attributed to increase of charge carrier (Ag+ ions) energy with rise in temperature. It is also foimd to increase with increasing concentration of Ag ion precursor (inset of Fig.l7). This potentiality can lead to development of novel biosensors for biotechnological applications such as DNA detection. 

Fig. 17. Variation of conductivity of Ag-starch nanocomposites with temperature. Inset shows variation with concentration of silver nanoparticles.

This process is highly suitable for rubbers with poor solubility. In this process, the rubber sheet is soaked in TEOS or quite often in TEOS-solvent mixture and the in situ sUica generation is conducted by either acid or base catalysis. The sol-gel reaction is normally carried out at room temperature. Kohjiya et al. [29-31] have reported various nonpolar mbber-silica hybrid nanocomposites based on this technique. The network density of the rubber influences the swelling behavior and hence controls the silica formation. It is very likely that there has been a graded silica concentration from surface to the bulk due to limited swelling of the rubber. This process has been predominantly used to prepare ionomer-inorganic hybrids by Siuzdak et al. [48-50]. 

Okamoto et al. [48] first conducted an elongation test on PP-based nanocomposites in the molten state at constant Hencky strain rate, so using elongation flow optorheo-metry [49]. They also attempted to control the alignment of the dispersed silicate... 

A colloidal suspension of conductive vanadium pentoxide [130] can be used to perform intercalation, adsorption or encapsulation of electroactive molecules or biomolecules for electrodes or biosensor realization [131]. Encapsulation of glucose oxidase in nanocomposite films made with polyvinyl alcohol and V205 sol-gel matrix or in ferrocene intercalated V2Os sol-gel [132] were envisaged to prepare glucose biosensors. 

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