Composites, electrochemical properties adhesion

Tailored properties—Theories are needed for predicting the structure, composition, properties, adhesion, and uniformity of electrochemical and plasma-generated surface films in order to control microscale phenomena. 

The pH of the carbon blacks is used to indicate their relative acidity or basicity, because the properties of these materials (i.e., adhesion and charge injection in carbon-polymer composites, electrochemical behavior) depend sensitively on the surface chemical and electronic sfructure [174, 222, 223]. This parameter is usually related to the amount of chemisorbed oxygen present on the surface, and to the very small amount of water soluble salts present in the material. The pH of carbon blacks is neutral to slightly alkaline for most grades, due to the low amount of chemisorbed species. To enhance certain properties, carbon blacks can be oxidised, with a subsequent increase in the amount of chemisorbed oxygen groups. These carbon blacks, therefore, show an acidic pH values, and relationships have been reported between the pH of carbon blacks and their content of volatile matter [223]. 

The materials discussed in this section are polyaromatic polymer/anion composite films prepared electrochemically by the polymerization of the derivatives of pyrrole, aniline, thiophene, azulene and benzene. The films are normally used directly as grown on the metal substrate where they have good adhesion and electrical contact. The switching properties of these materials are described with more detail in the first section which describes polyaniline. However, it should be understood that these characteristics are generally common to all of the materials. 

Carbon fibers, when used without surface treatments, produce composites with low mechanical properties. This has been attributed to weak adhesion and poor bonding between the fiber and matrix. Therefore, the carbon fibers are given surface treatments, the exact nature of which is a trade secret. This surface treatment increases the surface active sites which results in the improvements of the bonding between the fibers and the resin matrix. This tends to increase the wettability of the carbon fibers and enhances the mechanical properties [4-7]. Surface treatments may be classified into oxidative and nonoxidative treatments. An oxidative treatment involves gaseous oxidation, liquid-phase oxidation carried out chemically or electrochemically and catalytic oxidation. The nonoxidative surface treatments involves deposition of more active forms of carbon or metals such as whiskerization, pyrolytic coating, the grafting of the polymers, and metal deposition on the carbon fiber surfaces [8-11]. 

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