X-ray structural studies of lamellar and cubic phases in the ternary system hexadecyl-dimethylethyl ammonium bromide/water/n-decanol

The influence of n-decanol on the formation of the lamellar and cubic phase s in the ternary system was studied by X-ray diffraction measurements. The studies I-elate to previously published results [2-5] and focus on the stru ctural parameters of the lamellar and cubic phases. At a constant mol ratio of C(16)Me(2)EABr/n-decanol = 2.54 the average bilayer-thickness of the la mellar phase is D-L = 31.5 Angstrom. This can be understood in terms of the presence of fluid hydrocarbon chains of the surfactant and cosurfactant in the bilayer. At a constant composition of the ternary system the proper ti es of both cubic phases Q(alpha,1) and Q(alpha,2) are markedly dependent on the temperature. At T = 318 K the cubic unit cell of the Q(alpha,1) phase is face-centered and is identical with the space,group Fd3m with an edge le ngth of a = 588 Angstrom. Above T = 320. 5 K a space-centered space group I m3m with art edge length a = 438 Angstrom 1 vas found for the cubic phase Q (alpha,2).