Temperature dependence of the cell parameters of Fischer-Tropsch waxes: hard wax and oxidised hard wax

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Abstract
The cell dimensions of two Fischer-Tropsch waxes, namely hard wax and oxidised hard wax, have been measured as a function of temperature from 80K to the melting points. Above room temperature the expansion of the lattices is less dramatic than in the n-alkane C33H68 but it is also mainly in the b direction. Potential energy calculations show that the most probable motion of the chains is a 90 degrees correlated jump between two potential energy minima. This motion seems to change to 180 degrees correlated jumps at the phase transition I to II. The relative orientations of the molecules show that these jump motions should result in an expansion of the lattice mainly in the b direction. The transition II to III observed in oxidised hard wax was not observed in hard wax.