Processing of electroceramic-polymer composites using the electrorheological effect
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This paper presents a novel approach that demonstrates the usefulness of electrorheological fibril formation to form f-3 connected ceramic-polymer composites. These fillers include ferroelectric, polar, metal, semiconductor, and superconductor crystallite powders. Patterned distributions of ceramic fillers within the polymer matrix can be induced by electric fields applied between patterned electrodes.
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I. INTRODUCTION A. Electroceramic composites The study of electroceramic composites has resulted in several new families of devices with properties superior to those obtained from single phase materials.1"3 Typically, the success of such composites can be traced to a well-designed connectivity of each phase making up the composite. Where connectivity is defined as the number of dimensions, a component phase is connected. These connectivity patterns enhance the anisotropy of property coefficients and control transport of heat, charge, and radiation. These connectivity patterns can take on a number of forms. A full nomenclature has been described for diphasic and triphasic component composite systems alike. For readers unfamiliar with this nomenclature and wish to read more, we refer them to Ref. 3. This study involved two diphasic connectivity patterns, namely the subgroups 0-3 and 1-3. These diphasic connectivity patterns are schematically demonstrated in Fig. 1. The 0-3 case that refers to the active filler phase has zero connectivity, while the inactive matrix phase has three-dimensional connectivity, i.e., a dispersed phase in a surrounding matrix. The 1-3 case refers to a filler phase having connectivity in one dimension, while the matrix phase is continuous in all three dimensions. With many early electroceramic composites, the size of the connected phase has been on a scale (>100 /xm) that could be processed with conventional processing techniques.1"3 Hence, desirable composite connectivity patterns could be readily obtained. However, present day and future requirements of component miniaturization bring with it difficulties in assembling more complex connectivities. These difficulties primarily are associated with the mechanical assembly of the component parts
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FIG. 1. Schematic representation of the diphasic connectivities 0-3 and 1-3.
and the strong interparticle forces between individual filler components. Engineers and materials scientists are forced to exploit self-assembling composite systems to control intelligently the phase or component segregation. Such examples of self-assembly include unidirectional solidification of eutectic compositions or ceramics of aligned polar-crystallites.4"8 However, these types of self-assembly are exceptional cases and not applicable to all composite systems. Ceramic-polymer and metalpolymer composites require other methods to align or assemble the filler phase. Magnetic fillers have been shown to align under magnetic fields, but of course this has its limitation to paramagnetic or ferromagnetic fillers.910 Other methods of assembling fillers in cerami
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