<P> The unique crystal orientation of confined polymers imparts anisotropic properties . In one example the large, in - plane polymer crystals reduce the gas permeability of nanolayered films by almost 2 orders of magnitude . </P> <P> The fraction of the ordered molecules in polymer is characterized by the degree of crystallinity, which typically ranges between 10% and 80% . Higher values are only achieved in materials having small molecules, which are usually brittle, or in samples stored for long time at temperatures just under the melting point . The latter procedure is costly and is applied only in special cases . </P> <P> Most methods of evaluating the degree of crystallinity assume a mixture of perfect crystalline and totally disordered areas; the transition areas are expected to amount to several percent . These methods include density measurement, differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy and nuclear magnetic resonance (NMR). The measured value depends on the method used, which is therefore quoted together with the degree of crystallinity . </P> <P> In addition to the above integral methods, the distribution of crystalline and amorphous regions can be visualized with microscopic techniques, such as polarized light microscopy and transmission electron microscopy . </P>

Why polymers are generally solids at room temperature