Electroactive composites

This chapter discusses materials known as electroactive composites. These are mixtures of an electroactive (or in the present context, ferroelectric) ceramic phase and a polymer phase. Early sections will look at the individual phases, making use of piezoelectric parameters defined in Chapter 5. A summary of theoretical models will then be given, before preparation and characterization are discussed. Finally, the problems associated with producing an active device and examples of working systems will be considered. 

Composite materials have been known for many thousands of years. Among the earliest uses were the boat-building materials prominent in the Middle East about 5000 bc composed of reeds with a pitch binder and the laminated wood composites crafted in Thebes around 1500 BC. From the early days of the polymer industry, it was appreciated that the final properties of polymers could be significantly enhanced by the use of inorganic fillers to form a composite. Today fillers are routinely used to tailor properties such as thermal expansion, conductivity, flammability and mechanical performance, and even to reduce cost. 

Normally the filler is an inert inorganic powder or fibre. However, among the modern composites most actively investigated at present are those classified as electronic composites. Multilayer dielectric materials and piezoelectric ceramic-polymer composites are becoming of particular importance as technological and industrial advances demand more versatile and responsive transducer devices. 

For many years piezoelectric ceramics have been the conventional materials used in transducer applications, the most important being lead zirconate titanate (PZT). PZT is derived from the solid solution of two perovskite materials, tetragonally distorted PbTi03 and rhombohedral PbZr03. The anisotropic nature of this material, especially at the 

In hydrostatic mode the piezoelectric strain coefficient is deter- 

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Lyons, M.E.G. 1994. Electrocatalysis using electroactive polymers, electroactive composites and microheterogeneous systems. Analyst 119, 805-826. 

Ionic Liquid-Assisted Fabrication of Graphene-Based Electroactive Composite Materials... 

Conductive materials in fibrillar shape may be advantageous compared to films due to their inherent properties such as anisotropy, high surface area, and mechanical strength. Fibrous conductive materials are of particular interest in electroactive composites. Fine metal nanoparticles, carbon fibers, and carbon nanotubes have been efficiently distributed in an insulating polymer matrix in order to improve both electrical and mechanical properties. 

A polyanrline-poly(butyl acrylate-vinyl acetate) composite exhibiting electroactivity and having a conductivity of 2.2 S/cm was prepared by emulsion polymerization. The composite was soluble in common organic solvents and a stable water-based dispersion could also be prepared. Films cast from aqueous media had exceptional mechanical properties and had excellent adhesion to steel [144]. From the same group, a polyaniline and polyvinyl alcohol electroactive composite has been synthesized by... 

One option to develop artificial muscles is the use of electroactive polymers (EAPs) or electroactive composite structures based on polymers. These materials or stmctures are able to convert electrical energy into mechanical energy. Different types of materials and stmctores with different properties are explored for many applications (Bar-Cohen, 2004). 

By convention, in electroactive composites, the first number refers to the active phase and the second to the inactive phase. The connectivity patterns for more than two phases are basically similar to the diphasic patterns, but are far more numerous. For n phases, the number of connectivity patterns is (n + 3) /3 n , producing 20 three-phase and 35 four-phase patterns. 

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