Evidence of a phase transition in the rotator phase of the odd-numbered paraffins C23H48 and C25H52

We present here a study of the ’’rotator phase’’ displayed by the odd-numbered paraffins CnH2n+2 with n = 23 and n = 25. From x-ray and D.S.C.(differential scanning calorimetry) experiments we show that the so-called rotator phase of these compounds exhibits a phase transition from a pseudohexagonal symmetry modification to a hexagonal symmetry modification when increasing the temperature. The corresponding phase transition seems to be a weak, first order transition.