Recording materials Anisotropic films

If the material is heterogeneous or anisotropic, it will have different thermal expansions depending on the direction in which they have been measured. For example, a composite of graphite fibers and epoxy will show three distinct thermal expansions corresponding to the X, y, and z directions. Blends of liquid crystals and polyesters show a significant enough difference between directions for the orientation of the crystals to be determined by TMA. Similarly, oriented fibers and films have a different thermal expansivity in the direction of orientation to that in the unoriented direction. This is normally addressed by recording the CTE in the x, y and z directions (Fig. 6A). Bulk measurements or volumetric expansion can be made by dilato-metry as shown in Fig. 6B and this is discussed in detail below. 

The photochromic and photo-induced anisotropic properties of materials can be used in ordinary and polarization holographic recording resp>ectively. It is known that fulgide-doped polymeric films are photochromic and photo-induced anisotropac, which can be used for both. 

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