Electrical and Thermal Properties

The use of organic nanofillers allows the reduction of the filler content required to achieve high thermal conductivity. In particular, multi-walled carbon nanotubes (MWCNTs), with their one-dimensional structure, high aspect ratio and superior thermal conductivity (3000 W/mK for an individual MWCNT and 200 W/mK for bulk MWCNTs at room temperature (Yang et al., 1991)) have recently attracted great attention in the scientific world. The influence of different carbon nanotube types, particle content, interfacial area, surface functionalization and aspect ratio on the electrical and thermal conductivity of epoxy resins has been investigated (Gojny et al., 2006). 

It has been shown that, by adding 6% in weight of multi-walled carbon nanotubes or 71.7% in weight of silicon carbide (SiC) microparticles to an epoxy resin, the thermal conductivity of the composites reached values that are 2.9 and 20.7 times that of the neat epoxy, respectively (Zhou et al., 2010). Moreover, to further improve the thermal conductivity of the composites, these authors partially replaced microfillers with nanofillers to obtain a 

Carbon nanotubes decorated with silver nanoparticles (Ag-CNTs) have been used as conducting fillers in epoxy resin to fabricate electrically conducting polymer (Ma et al., 2008). The experimental results have shown that the electrical conductivity of composites containing 0.1 % in weight of Ag-CNTs was more than four orders of magnitude higher than those containing the same content of functionalized CNTs, and this improvement was not at the expense of thermal or mechanical properties. 

In recent years metallic particles have also been considered as fillers to increase the electrical and thermal conductivities of epoxy systems. The electrical and thermal conductivities of epoxy systems filled with metal (i.e. copper and nickel) powders have been studied (Mamunya et al., 2002). In this work it was shown that the composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. The percolation theory equation holds true for systems with a random distribution of dispersed filler, while in contrast to the electrical conductivity, the dependence of thermal conductivity on concentration shows no jump in the percolation threshold region. 

Thermal, mechanical chemical and fracture properties of epoxy resins filled with alumina particles have been analyzed as a function of average filler size, size distribution, particle shape, loading and epoxy cross-link density (McGrath et al, 2008). The authors have shown that the density of cross-link and the amount of filler were the most important variables, modifying all properties, while other parameters (i.e. particle size, shape and size distribution) have little impact on the final properties. 

Huang et al. (39) reported that in polyamide (PA 11) nanocomposites, the incorporation of nanotubes led to the increase in the peak degradation temperature of the polymer. At an amount of 1 wt% nanotubes in the composites, the peak degradation temperature was enhanced by 20 °C. However, the degradation temperature reduced at higher concentrations of nanotubes probably owing to the aggregation of the nanotubes in the composites. 

Giraldo et al. (38) reported polyamide 6 nanocomposites in which the crystallization temperature of the polymer was observed to increase with the addition of 2 wt% CNTs. The temperature was 185°C for the pure polyamide which subsequently increased to 190 °C. The authors suggested that the nanotubes might serve as the nucleation sites for the polymer crystals to grow which was also confirmed by the reduction of the chain mobility by dynamic mechanical analysis. The thermal stability of the composites was reported to enhance after the incorporation of nanotubes. 

The incorporation of nanotubes into thermotropic liquid crystalline polymer (TLCP) was reported to enhance the thermal decomposition temperatures and the residual yields of the nanocomposites (35). It was reported that the nanotubes act as protective barriers in the nanocomposites against thermal decomposition and are likely to retard the thermal decomposition of the TLCP nanocomposites owing to building of barrier to hinder the transport of volatile decomposed products out of the nanocomposites. 

Interesting thermal response of the polystyrene nanocomposites was reported when untreated and polystyrene grafted nanotubes were used for the reinforcement of polymer (49). The glass transition temperature of the pure polystyrene matrix was observed to be 99 °C. Similar transition temperature of 98 °C was observed for the composites containing 2.5 vol% of the untreated nanotubes. The nanocomposites containing polymer functionalized nanotubes 

Numerous other studies on the nanotube nanocomposites have been reported which demonstrate other properties like optical, morphological, fiber surface properties etc. Saini et al. (52) measured the UV absorption spectra of the poly(3-hexylthiophene) (P3HT) and its nanocomposites with varying amounts of nanotubes. The absorption band for pristine P3HT was observed at 505 nm which shifts toward the higher wavelength region on the addition of nanotubes 

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R. E. Schawmm, A. E. Clark, and R. P. Reed,M Compilation and Evaluation of Mechanical, Thermal and Electrical Properties of Selected Polymers, NBS Report, A EC SAN-70-113, SANL 807 Task 7, SANL Task 6, National Technical Information Service, U.S. Dept, of Commerce, Springfield, Va., Sept. 1973, pp. 335-443. 

Phenol—formaldehyde resins are used as mol ding compounds (see Phenolic resins). Their thermal and electrical properties allow use in electrical, automotive, and kitchen parts. Other uses for phenol—formaldehyde resins include phenoHc foam insulation, foundry mold binders, decorative and industrial laminates, and binders for insulating materials. 

A number of HFIP-derived polyethers are known which exhibit good mechanical, thermal, and electrical properties (112,113). Aromatic polyethers have been synthesi2ed from bisphenol A (R = H) or AF (R = F) and fluorkiated aromatics (Ar = perfluorophenyl, perfluorobiphenyl, or... 

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

RYTON Polypheny lenesulfide Physical, Chemical, Thermal, and Electrical Properties, TSM-266, Phillips Chemical Co., BaiflesviUe, OHa., Api. 1981, p. 2. 

The number of hardening agents used commercially is very large and the final choice will depend on the relative importance of economics, ease of handling, pot life, cure rates, dermatitic effects and the mechanical, chemical, thermal and electrical properties of the cured products. Since these will differ from application to application it is understandable that such a wide range of material is employed. 

Silicone rubbers find use because of their excellent thermal and electrical properties, their physiological inertness and their low compression set. Use is, however, restricted because of their poor hydrocarbon oil and solvent resistance (excepting the fluorosilicones), the low vulcanisate strength and the somewhat high cost. 

The above data represent the first from composites fabricated with fixed catalyst VGCF. A review of the data leads to the conclusion that the thermal and electrical properties of this type of carbon fiber are perhaps the most likely to be exploited in the short term. While mechanical properties of the composites are not as attractive as the thermal and electrical, it may be noted that no effort has... 

As part of an effort to develop high-performance, high-temperature-resistant polymers for microelectronics applications, we also recently described a series of both partially fluorinated and nonfluorinated poly(aryl ether ketone)s containing amide, amide-imide, cyano oxadizole, or pyridazine groups and characterized their thermal and electrical properties.11... 

Enhancement of thermal and electrical properties of carbon nanotube polymer composites by magnetic field processing. J. Appl. Phys. 94 6034-6039. 

A number of physical tests emphasizing stress-strain behavior will be covered in Chapter 14. Here, we will concentrate on other areas of testing, emphasizing thermal and electrical properties and on the characterization of polymers by spectral means. Spectroscopic characterization generally concentrates on the structural identification of materials. Most of these techniques, and those given in Chapter 14, can also be directly applied to nonpolymeric materials such as small organic molecules, inorganic compounds, and metals. 

Highly pure lanthanum oxide is used to make optical glass of high refractive index for camera lenses. It also is used to make glass fibers. The oxide also is used to improve thermal and electrical properties of barium and strontium titanates. Other applications are in glass polishes carbon arc electrodes fluorescent type phosphors and as a diluent for nuclear fuels. In such apph-cations, lanthinum oxide is usually combined with other rare earth oxides. 

The wide structural diversity in the tricyclic compounds considered in this chapter ensures that they have found an equally diverse range of applications. The applications previously outlined <1996CHEC-II(7)841> have continued to be important and have been further developed. Carbocyclic anhydrides and imides continue to find application for the synthesis of polymeric materials which are used extensively in microelectronics due to their excellent thermal and electrical properties <2001PP03>. Similarly, polymers containing benzobisthiazoles, benzobisoxazoles, and... 

A recent review [1] on polyimide adhesion to metal and ceramic surfaces shows the relevance of this topic to many different technological areas. Of all the polyimides studied thus far, it is evident that the most popular one is PMDA-ODA. It has very good mechanical, thermal, and electrical properties, but it suffers from poor adhesion characteristics. This problem is often overcome by the application of an adhesion promoter to the surface of interest. The most popular adhesion promoter appears to be APS. An excellent review concerning APS has been written by Ishida [2]. A wealth of information concerning silane coupling agents can also be found in the book by Plueddemann [3],... 

Typical metallic substances have structures which cannot readily be described either in terms of directional covalent bonds or as arrays of cations and anions. Metallic elemental substances exhibit high coordination numbers, and can - to a first approximation - be viewed as arrays of cations embedded in a sea or glue of electrons completely delocalised over the crystal. This model helps to explain the characteristic mechanical, thermal and electrical properties of metals. It is also consistent with... 

As carbon nanotubes present exceptional mechanical, superior thermal and electrical properties in general, by using them as reinforcing elements there are high expectations for improvement of quality of nano- and microcomposites [14-18]. As shown from earlier measurements, through carbon nanotube addition a 15-37% improvement of mechanical properties (elastic modulus and strength) can be achieved in comparison to other carbon-filled samples [19]. 

Polyimide (PI) caps all other polymers in its temperature range of use (-200 to 260 °C in air short-time even up to 500 °C). Because of its high price, it is used in special cases only, such as space vehicles, nuclear reactors and some electronic parts. Newer developments, related to polyimide, are the polyether imides (e.g. Ultem ), polyester imides and polyamide imides (e.g. Torlon ), all with very good mechanical, thermal and electrical properties and self-extinguishing. 

The substrates carrying the circuits shown in Fig. 4.5 are a 95-96% alumina. This ceramic has been adopted for its combination of physical and chemical characteristics and, importantly, low cost. It offers a combination of mechanical, thermal and electrical properties which meet the in-service requirements, and compositional and microstructural characteristics suited to thick film printing (see Section 4.2.2). Alumina substrates are manufactured on a very large scale making the unit costs a small fraction of the total circuit cost. 

Carbon nanotubes (CNTs) have shown exceptional stiffness, strength and remarkable thermal and electrical properties, which make them ideal candidates for the development of multifunctional material systems [22], Nowadays, CNTs are dispersed within polymer in order to improve their mechanical and electrical properties [23], Therefore, reinforcement of PB films by CNTs might be a strategy for manufacturing mechanically robust ion-... 

These versatile plastics are available in many grades as well as copolymers like ethylene propylene. NEAT PP has a low density of 0.90, which, combined with its good balance of moderate cost, strength, and stiffness as well as excellent fatigue, chemical resistance, and thermal and electrical properties, makes PP extremely attractive for many indoor and outdoor applications. There are hundreds of formulations that are produced. 

Carbon nanotubes represent high potential fillers owing to their remarkably attractive mechanical, thermal and electrical properties. The incorporation of nanotubes in the polymer matrices can thus lead to synergistic enhancements in the composite properties even at very low volume fractions. This chapter provides a brief overview of the properties and synthesis methods of nanotubes for the generation of polymer nanocomposites. 

Nanotube nanocomposites with a large number of polymer matrices have been reported in the recent years. The composites were synthesized in order to enhance mechanical, thermal and electrical properties of the conventional polymers so as to expand their spectrum of applications. Different synthesis route have also been developed in order to achieve nanocomposites. The generated morphology in the composites and the resulting composite properties were reported to be affected by the nature of the polymer, nature of the nanotube modification, synthesis process, amount of the inorganic filler etc. The following paragraphs review the nanocomposites structures and properties reported in a few of these reports and also stress upon the future potential of nanotube nanocomposites. 

The recognition of the unique properties of carbon nanotubes (CNTs) has stimulated a huge interest in their use as advanced filler in composite materials. In particular, their superior mechanical, thermal and electrical properties are expected to provide much higher property improvement than other nanofillers (18-22). For example, as conductive inclusions in polymeric matrices, CNTs shift the percolation threshold to much lower loading values than traditional carbon black particles. 

Carbon nanotubes (CNTs) are the strongest fibers that are currently known. They demonstrate amazing mechanical, thermal and electrical properties, while a low density and a very high aspect ratio (1-5). A lot... 

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