Crystal structure of modulated n-paraffin binary solids

The solid formed after a metastable solid solution, composed of n-C30H62 and n-C36H74, demixes, after being held within a miscibility gap, is a commensurately modulated superstructure. For a specific molar concentration, electron diffraction measurements on epitaxially oriented specimens indicate that, from the standpoint of both superlattice spacings and intensities, the same average chain packing is maintained for all microcrystalline areas. Direct crystallographic phasing methods were used to determine the structures of nearly 0.6/0.4 and 0.4/0.6 molar ratio combinations. Molecular packing models suggested from the crystal structure analyses lead to predicted Okl intensities that are in reasonable agreement with the observed data (R = 0.25). It is clear that, as described earlier, a longitudinal sequence of essentially pure components exists. In addition, there must be a lateral association of different chain length domains within a given layer, in agreement with earlier vibrational spectroscopic measurements.