2H and 13C nuclear magnetic relaxation studies of the cubic liquid-crystalline phase I1 in the sodium octanoate–octane–water system

Abstract

An extensive n.m.r. relaxation study of the cubic I₁ phase formed in the sodium octanoate–octane–water system is presented. ¹³C relaxation data are presented at three magnetic field strengths and ²H relaxation data at twelve magnetic field strengths (from 0.3 to 8.5 T). All the relaxation data depend on the magnetic field strength. The data are analysed with the ‘two-step’ model of relaxation, and information concerning both the dynamic (correlation times) and static (order parameters) properties of the hydrocarbon chains in the surfactant aggregates are obtained. Comparisons are made with results from sodium octanoate–water in other phase situations. As regards the structure of the surfactant aggregates in the I₁ phase, the relaxation data support the structure of hemisphere-capped rods suggested by Fontell et al.(K. Fontell, K. V. Fox and E. Hansson, Mol. Cryst. Liq. Cryst., 1985, 1, 9.) In particular, it is shown that the complete set of ²H relaxation data can be rationalized with the two-step model, if the axial ratio of the hemisphere-capped rods is ca. 1.3 to 1.