Spin-lattice relaxation in anhydrous sodium and lithium soaps between 23° and 180°C

Abstract

The influence of molecular motions on the spin-lattice relaxation in even- and odd-numbered sodium and lithium soaps between 23 and 180δC has been investigated. The crystalline transition in most sodium soaps can hardly be observed from T 1 measurements as a result of a broadened correlation-time distribution. The T 1 values show that the oscillation amplitude increases and the correlation-time distribution narrows with increasing chain length. The Tl values alternate such that at this temperature the even-numbered soaps presumably have a closer packing than the odd-numbered ones. The crystalline-subwaxy and subwaxy-waxy transitions are observable in only one T 1 minimum. The amplitude of the motions increases as the chain becomes longer. There is a slight alternation in the T 1 minima of the even- and odd-numbered soaps, which again points to a closer packing of the even-numbered sodium soaps. The lithium soaps show a transition to another crystalline phase between 85 and 115°C in which phase the chains are less tilted. The increased mobility is observable from a decrease of T 1.