Small-angle X-ray scattering studies of micelle formation in the binary system hexadecyl dimethylethyl ammonium bromide/water

In the micelle-forming concentration range of the binary system hexadecyl d imethylethyl ammonium bromide (C(16)Me(2)EABr)/water, the size, geometry an d average aggregation number of the micelles were determined from the Guini er plot by small-angle X-ray scattering In the concentration range c.m.c.>c (S)<12% w/w, the scattering curves satisfy the Guinier plot for spherical m icelles. From surfactant concentrations of c(S)>17% w/w C(16)Me(2)EABr, rod -shaped micelles occur, which then with increasing surfactant concentration form the lyotropic-nematic rod phase (N-C). The parameters for spherical m icelles and rod micelles (sphere radius, electron density average aggregati on number, rod length, cylinder cross section) resulting from the X-ray sca ttering studies are described and compared in detail as functions of the C( 16)Me(2)EABr concentration. In addition, the existence regions of the following lyotropic mesophases wi th increasing C(16)Me(2)EABr concentration were fixed in the form of a bina ry phase diagram. N-C phase (lyotropic-nematic rod phase), H-alpha phase (h exagonal phase), M-alpha phase (2-dimensional, monoclinic phase from flatte ned band micelles), Q(alpha) phase (cubic phase), L-alpha phase (lamellar p hase, fluid chains) and L-beta phase (lamellar phase, rigid chains). Detail s of this will be discussed in our next paper [14].