Amorphous material that transmits

The chalcogenides are all insoluble in water and other common solvents. ZnSe and CdTe have excellent transmission characteristics. The only problem with these materials is their high refractive index, which leads to high front-surface reflectance (see Section 13.2.2), so that transmission spectra of liquids held in cells fabricated from these materials often give rise to interference fringes (see Section 11.1.3). These materials aU make excellent internal reflection elements. AMTIR (amorphous material that transmits infrared radiation) is a mixture of several chalcogenides. Many optical fibers used for mid-infrared spectrometry are made from this material (see Section 15.4). 

A noncrystalline polymeric material that has no definite order or crystallinity. A polymer in which the macromo-lecular chain has a random conformation in solid (glassy or rubbery) state. On the one hand, an amorphous polymer may show a short range order, while on the other, a crystalline polymer may be quenched to the amorphous state (viz., polyethylene terephthalate (PET)). The maximum value of a periodically varying function, e.g., used to describe the energy transmitted from the ultrasonic welding horn to the weld joint. 

Generally, polymers that crystallize are not considered good candidates for membrane materials however, there are some exceptions [26, 27]. The presence of crystallinity reduces permeability [28,29] and good membranes should be capable of high fluxes. The usual physical picture is to think of a semicrystalline polymer in terms of a simple two-phase model one phase being amorphous and the other being crystalline. In the typical case, the crystals do not sorb or transmit penetrant molecules the following relationship has been proposed [28, 29] to describe the extent to which crystallinity reduces permeability from that if the polymer were amorphous... 

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