REVERSED HEXAGONAL PHASE-STRUCTURE IN LITHIUM PHENYLSTEARATE

The structure of the reversed hexagonal1 phase and the reversed hexago nal (H-2) --> (H2) reversed hexagonal (H-2) phase transition in anhydr ous lithium phenylstearate have been investigated using FTIR spectrosc opy. CH2 wagging vibrations from {gtg} and {gg} conformers indicate co nsistently smaller number of than would be expected from the rotationa l isomeric state model, although the number of {gtg} conformers approa ches the predicted value at the H2 phase transition. The IR results en abled the alkyl chain extension to be calculated, as a function of tem pemture. A new model of chain packing at the ionic core surface allowe d the core radius (r(c)) to be estimated (5.6 angstrom less-than-or-eq ual-to r(c) less-than-or-equal-to 7.1 angstrom). In combination with t he chain extension, an overall cylinder diameter was calculated. By th e onset of the H2 transition, this dimension had decreased to a figure less than the X-ray lattice spacing. It is concluded that interdigita tion of alkyl segments has then reduced sufficiently to allow translat ional and rotational freedom for the cylinders to become more closely packed. Changes in chain conformation are therefore seen as the drivin g force for the phase transition, allowing the X-my lattice spacing to decrease.