ANISOTROPIC NANO COMPOSITES
Anisotropic materials and structures inherently have unique properties and applications. Polymerrlayered sili- cate nanocomposites represent good examples of such materials with attractive properties, including high me- chanical moduli, heat resistance, barrier behavior, ion-ex- change capability. A comprehensive review of the prepa- ration, characterization, properties and processing of polymerrlayered silicate nanocomposites can be found in wx 29 . Technologies have been developed so that layered silicates can be incorporated into most types of polymers and nanocomposites can be formed through melt-mixing
Chemical structure of phyllosilicates, a typical nanoclay whose crystal structure consists of layers made up of two tetrahedrally wx coordinated silicon atoms fused to an edge-shared octahedral sheet of either aluminum or magnesium hydroxide 29 . The layer thickness is about 1 nm, and the lateral dimensions of these layers may vary from 30 nm to more than several microns. There are three different types of wxthermodynamically achievable polymer rlayered silicate nanocomposites, namely, intercalated, intercalated-and-flocculated and exfoliated 29 . With proper orientation, such layered silicate nanocomposites have remarkable anisotropic properties as shown schematically, i.e., vertical Ž. barrier corona resistance properties and lateral energy dissipation through confined ionic conduction. Such anisotropic electrical and thermal properties are of great use for rotating machine insulation.
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