X-ray scattering and disordered structure of n-tetracosane in urea adducts. I. A model for the x-ray scattering pattern

The x-ray scattering pattern of a single crystal of n-tetracosane-urea adducts was investigated by photographic and counter methods. Two different kinds of diffuse scatterings were found in addition to Bragg reflections; s-diffuse scattering and d-diffuse scattering. The s-diffuse scattering exists on the layers corresponding to the molecular length of n-tetracosane and its width along the c* axis is as sharp as that of the Bragg reflections. The d-diffuse scattering exists on the layers corresponding to the repeating period of C2H4 units and the width is broad. The two-dimensional distribution normal to the c* axis of the intensity of the diffuse scattering shows maxima on hexagonal reciprocal lattice points. A model is proposed on the assumption that the n-alkane molecule has a translational displacement along the chain axis and a rotational displacement around the chain axis. The model can reproduce the observed x-ray scattering pattern and gives us three different spatial correlation lengths.