Abstract. X-ray diffraction measurements are made for urea adducts with n-eicosane to investigate the arrangement of n-eicosane molecules in the channels formed by urea molecules. Extra Bragg reflections have been found on the layers with the -coordinate corresponding to twice the chain length of the n-eicosane molecule in both the low- and high-temperature phases. This kind of Bragg reflection has not been observed for other n-alkanes in urea adducts. On the basis of the intensity distribution of the extra Bragg reflections, it is found that the n-eicosane molecules are arranged in such a way that the orientations of zigzag planes of longitudinally neighbouring molecules are anti-parallel to each other.

Print publication: Issue 13 (25 March 1996)
Received 27 November 1995, in final form 2 February 1996