What makes a material conductive?.
In many materials, such as crystals, stretched polymers or liquid crystals, macroscopic properties such as.
strength and optical and electrical properties generally depend on direction. They are said to be anisotropic.
Similarly, the material's electrical conductivity may depend on direction and be anisotropic. Three simple.
carbon compounds are diamond, graphite and polyacetylene. They may be regarded, respectively, as three- ,.
two- and one-dimensional forms of carbon materials (Fig. 3). Diamond and graphite are modifications of pure.
carbon, while in polyacetylene one hydrogen atom is bound to each carbon atom.
(d).
FIGURE 3.
Three-, two- and one-dimensional carbon materials: diamond (a) and graphite (b) crystal lattices, and.
polyacetylene chain (c). An alternative way of writing polyacetylene is also shown (d).
Diamond, which contains only bonds, is an insulator and its high symmetry gives it isotropic properties.
Graphite and acetylene both have mobile electrons and are, when doped, highly anisotropic metallic.
conductors. The conductivity is about one million times greater in the plane of the graphite rings than at right.
angles to this plane: (parallel)/(perpendicular) = 106 . Correspondingly, the conductivity of stretchoriented.
polyacetylene is some 100 times higher in the stretch direction than perpendicular to it. The smaller.
4.
anisotropy compared to graphite, i.e. non-vanishing(perpendicular), could suggest -short-circuiting- across.
the chains. Since the polyacetylene chains are not infinite, contacts between them are important if the material.
is to be macroscopically conductive. This could thus explain the lower conduction anisotropy compared to.
graphite.
Anisotropy is also interesting in other contexts of stretch aligned polymers: when the absorption of light is.
anisotropic the material acts as a polariser. Also mechanical strength is anisotropic: aligned polyacetylene.
fibers are known to be very strong along the orientation direction.
