Crystal Structure of Wax Lamellar InterfacesA Residual Petroleum Fraction Characterized by Electron Crystallography

After a multicomponent paraffin assembly was constructed to model a petroleum residue wax ( M w / M n = 1.009), its structure was characterized by electron crystallography. Consistent with a single lamellar spacing, two endotherms in a DSC scan are typical of paraffin chain solid solutions and represent the premelt transition to a “rotator” phase and the true melt. The average chain packing in the crystal structure is that of the paraffin n -C 32 H 66, in space group Pca 2 1 with a = 7.42, b = 4.96, and c = 85.0 Å. An attempt to account for the lamellar disorder with a chain-end occupancy model based on the chemical distribution of chain lengths is only partially successful. A better fit is found when lower chain-end occupancies are used. This discrepancy could be due to conformational defects in which the chain end atoms do not lie on strict methylene subcell lattice sites.