SELF-ASSEMBLY IN SYSTEM OF LECITHIN AND NONIONIC AMPHIPHILE FROM NMR-STUDIES

Triton X-100 and water are mutually soluble at 305 K giving an isotropic solution. The binary solution can solubilize variable quantities of lecithin depending on sample composition, the maximum amount being 10 wt % of lecithin. The self-diffusion coefficients of Triton X-100, D(T), water, D(W), and lecithin, D(L) were measured with the Fourier transformed pulsed-gradient spin-echo (FT-PGSE) NMR technique. In the binary system, the D(W) values decrease continuously with increasing surfactant concentration (0-80 wt % surfactant), whereas there is a sharp decrease of the D(T) value until a minimum is reached, after which there is a slow increase in the diffusion coefficient of Triton X-100. The water diffusion data are analyzed with the cell diffusion model, and a constant hydration number, n = 6 (molecules of water per EO group), to be consistent with a water continous structure up to at least 80 wt % Triton X-100 at 305 K. The surfactant diffusion data are used to show the formation of nonspherical normal micelles even in the very dilute region, and the micelles undergo size and/or shape changes with increased Triton X-100. The micellar growth is more pronounced if the system contains lecithin. The D(T) and D(L) values are used to obtain the Triton X-100 monomer concentration, which is approximately equal to the cmc of Triton X-100 in water.