Internal friction study of polycrystalline n -paraffins

Recent measurements have shown that mechanical relaxation peaks commonly observed in n -paraffins are absent in single crystals of n -eicosane (C20H42). This work has now been extended to include polycrystalline samples of several highly pure long-chain hydrocarbons. Internal friction data obtained for a variety of n -paraffins, pure or otherwise, have revealed no low-temperature γ relaxation. Moreover, the α relaxation peak is suppressed completely by purification. In attempts to induce an α or γ loss peak, several dilute mixtures of other n -paraffins in pure C20H42 have been examined. Only the addition of odd-numbered shorter chains induced loss peaks. On the other hand, the presence of a branched impurity, in this case the C20H42 isomers 2-methylnonadecane and 10-methylnonadecane, did induce loss peaks, one of which correlates very well to the α process found in as-received C20H42. It is proposed here that isomer impurities are an important factor in the mechanics of many of the loss processes in long-chain hydrocarbons observed both mechanically and dielectrically.