Orientational order in liquid normal alkanes: An investigation using gas-chromatographic data

Using retention voluems, obtained from gas-liquid chromatography with then-alkanesn-C₂₈,n-C₃₂, andn-C₃₆ and the branched alkane squalane (2,6,10,15,19,23-hexamethyltetracosane) as the solvents and small branched andn-alkane molecules as solutes, excess chemical potentials were determined at 80, 100, and 120°C. From these data Flory'sX ₁₂ parameter was calculated, which is related to differences in force field and in orientatinal order of the two compounds. After correction for end effects, theX ₁₂ parameter in then-alkane solvents appeared to decrease with rising temperature and to increase with increasing chain length of then-alkane solvent. In addition,X ₁₂ was dependent on the shape of the order-disturbing substance. These results all point to the presence of short-range orientational order in liquidn-alkanes, which was deduced to occur before from enthalpies of mixing by Patterson and from depolarized Rayleigh scattering by Bothorel. In addition, it is shown that theX ₁₂ values are influenced by coupling of torsional oscillations of the molecules of the mixture components.