Additives for Modifying Electrical Properties

Some amino resins are used as additives to modify the properties of other materials. For example, a small amount of amino resin added to textile fabric imparts the familiar wash-and-wear quaUties to shirts and dresses. Automobile tires are strengthened by amino resins which improve the adhesion of mbber to tire cord (qv). A racing sailboat may have a better chance to win because the sails of Dacron polyester have been treated with an amino resin (1). Amino resins can improve the strength of paper even when it is wet. Molding compounds based on amino resins are used for parts of electrical devices, botde and jar caps, molded plastic dinnerware, and buttons. 

A variety of low-dielectric, low-loss resin systems are available for high-speed circuit apph-cations. These include polytetrafluoroethylene (FTFE or Teflon ), cyanate ester, epoxy blends, and allylated polyphenylene ether (APPE). Likewise, a few different reinforcements and fillers are available that can be used to modify the electrical properties of the base material. Although E-glass is stm the most commonly used fiberglass reinforcement, it should be noted that others are available. In addition, inorganic fillers are sometimes used to modify electrical properties as well. Table 9.6 provides electrical property data on some of the available fiberglass materials. Table 9.7 provides data on some of the base material composites available. 

Since the transverse shear wave may penetrate the damping surface layer and the viscous liquid, additivity of the equivalent electrical elements in the BVD circuit is only valid under certain particular conditions. Martin and Frye [53] studied the impedance near resonance of polymer film coated resonators in air with a lumped-element BVD model, modified to account for the viscoelastic properties of the film. In addition to the elements shown in Fig. 12.3 to describe the quartz crystal and the liquid, L/ and Rf were added to describe the viscoelastic film overlayer. For a small... 

Additives. There are many types of additives used by the papermaker to modify the physical and optical properties of the sheet. The most commonly used include kaolin and titanium dioxide for optical properties, starch for strength and rosin sizes for water repellency. All these materials can affect the electrical properties of the paper since they can eventually modify the nature of the interfiber contact as well as the fiber itself. These changes can influence the flow of charge through the sheet. 

The most desirable properties for electrically conductive polymeric materials are film-forming ability and thermal and electrical properties. These properties are conveniently attained by chemical modification of polymers such as polycation-7, 7,8, 8-tetracyanoqninodimethane (TCNQ) radical anion salt formation (1-3). However, a major drawback of such a system is the brittle nature of the films and their poor stability (4,5) resulting from the polymeric ionicity. In recent years, polymeric composites (6-8) comprising TCNQ salt dispersions in non-ionic polymer matrices have been found to have better properties. In addition, the range of conductivities desired can be controlled by adjusting the TCNQ salt concentration, and other physical properties can be modified by choosing an appropriate polymer matrix. Thus, the composite systems are expected to have important advantages for use in electronic devices. 

Polyaniline is an attractive electropolymerizable polymer for surface modifications due to its unique redox properties, high electrical conductance, and ease of preparation. In addition, polyaniline-modified surfaces retain a large specific surface area and can remain conductive facilitating subsequent electron transfer. Feng and coworkers [8] constructed a DNA impedance biosensor based on gold nanoparticle/pol5 niline nanotube membranes formed in the presence of chitosan as shown in Fig. 14.1. Chitosan was used... 

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