Fullerene-polymer matrix composites

The microhardness of films of fullerene-PE composites prepared by gelation from semidilute solution, using ultra-high-molecular-weight PE (6 x 10 ), has been also 

Comparison of X-ray scattering data and the microhardness valnes after annealing leads to the conclusion that there is phase separation of fullerene molecnles from the PE crystals within the material. Fnllerene-PE composites exhibit an unexpectedly large microhardness increase as the temperatnre is increased above 75 °C and this has been ascribed to the hardening of fnllerene aggregates within the composite (Balta Calleja et al, 1996). 

A new type of composite material starting from polymer blends has been developed. Due to the fact that the reinforcing elements are the basic morphological entities of oriented polymers, the microfibrils, these new composites have been named microfibrillar-reinforced composites (MFC) (Evstatiev Fakirov, 1992). MFC, however, clearly differ from traditional composite systems. Since the microfibrils are not available as a separate component, the classical approach to composite preparation is inappropriate for MFC mannfactnring. 

When MFC are prepared from blends of condensation polymers as a result of chemical reaction (additional condensation and transreactions) taking place at the 

The different stages of MFC manufacture schematically presented in Fig. 5.15(a) are better illustrated using a SEM and the selective extraction of the matrix (PA6) see Fig. 5.16. The PET microfibrils which play the role of reinforcing elements are rather impressive (Fig. 5.16(b)). As a result of profound chemical reactions, the microfibrils form aggregates involving the PA6 matrix (Fig. 5.16(c)). 

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Fullerene molecules may be incorporated into polymers in a variety of ways. A first, basic differentiation must be made between noncovalently embedded fullerenes (either isolated or aggregated) on the one hand and molecules covalently attached to the polymer strands on the other. The interaction between dispersed molecules or particles of fullerenes and their polymer matrix is clearly electrostatic. Their production is very simple. The desired amount of fullerene is added to the polymerizable material as a solid or in solution, and the polymerization is initiated. Transparent films of Qo/PMMA are an example of this class of composites, they contain separated Cso-molecules. The characteristics of both the fullerene and the polymer are conserved. 

Owing to its remarkable properties nanodiamond suits very well to being part of composite materials. In particular it is the small particle size, the hardness, the large chemical inertness, its nontoxicity and the high refractive index that may beneficially complement the properties of the polymer matrix. The latter may be connected to the diamond particles either by covalent bonding or by noncovalent interaction. Numerous examples of noncovalently bound composites have been reported in the literature (Section 5.6.1). StiU the interaction with the matrix is by far more complex than discussed for the nanotubes and fullerenes. This is due to the more variable surface structure that features not only graphitized domains, but also a variety of polar and nonpolar functional groups. 

From the material point view, there are two types of nanocomposites for OPVs organic particles (especially derivatives of fullerene Geo) in a polymer matrix and inorganic particles (semiconductors) in a polymer matrix. The host polymer for both groups is a hole conductor and plays the role of an electron donor. To contribute efficiently to the energy conversion, it should have a strong absorbance and a good electrical conductivity. Polymers such as MEHPPV and poly(3-hexylthiophene) (P3HT) are well adapted for composites. 

Nanocarbon structures such as fullerenes, carbon nanotubes and graphene, are characterized by their weak interphase interaction with host matrices (polymer, ceramic, metals) when fabricating composites [99,100]. In addition to their characteristic high surface area and high chemical inertness, this fact turns these carbon nanostructures into materials that are very difficult to disperse in a given matrix. However, uniform dispersion and improved nanotube/matrix interactions are necessary to increase the mechanical, physical and chemical properties as well as biocompatibility of the composites [101,102]. 

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