Investigation into the structures of binary-, tertiary- and quinternary-mixtures of n-alkanes and real diesel waxes using high-resolution synchrotron X-ray powder diffraction

Abstract

High-resolution X-ray powder diffraction using synchrotron radiation has been used to determine the unit-cell parameters of binary (n-C₂₀H₄₂ /n-C₂₁H₄₄ and n-C₂₀H₄₂ /n-C₂₂H₄₆), tertiary (n-C₁₉H₄₀ to n-C₂₁H₄₄ and n-C₂₀H₄₂ to n-C₂₂H₄₆) and quinternary (with alkanes ranging from n-C₁₈H₃₈ to n-C₂₆H₅₄) n-alkane mixed homologous systems, together with a number of real diesel waxes. The structures have been found to conform to the orthorhombic structure with four molecules per unit cell and space group Fmmm predicted by Luth et al.⁸ for binary mixtures. Line profile analysis of the powder patterns revealed the existence of incipient end-chain and interchain disorder; a crystal packing model consisting of interchain mixing, end-chain twisting and chain migration is proposed to account for the observed disorder.