REVERSED HEXAGONAL PHASE-STRUCTURE IN LITHIUM PHENYLSTEARATE

The structure of the reversed hexagonal1 phase and the reversed hexagonal (H-2) --> (H2) reversed hexagonal (H-2) phase transition in anhydrous lithium phenylstearate have been investigated using FTIR spectroscopy. CH2 wagging vibrations from {gtg} and {gg} conformers indicate consistently smaller number of than would be expected from the rotational isomeric state model, although the number of {gtg} conformers approaches the predicted value at the H2 phase transition. The IR results enabled the alkyl chain extension to be calculated, as a function of tempemture. A new model of chain packing at the ionic core surface allowed the core radius (r(c)) to be estimated (5.6 angstrom less-than-or-equal-to r(c) less-than-or-equal-to 7.1 angstrom). In combination with the chain extension, an overall cylinder diameter was calculated. By the onset of the H2 transition, this dimension had decreased to a figure less than the X-ray lattice spacing. It is concluded that interdigitation of alkyl segments has then reduced sufficiently to allow translational and rotational freedom for the cylinders to become more closely packed. Changes in chain conformation are therefore seen as the driving force for the phase transition, allowing the X-my lattice spacing to decrease.