STRUCTURE OF THE HEXAGONAL PHASE OF THE SODIUM DODECYL-SULFATE AND WATER-SYSTEM

The hexagonal cell parameter a of the system sodium dodecyl sulfate an d water in the H-alpha phase as a function of volume concentration c(n u) presents the functional behavior expected for rigid and finite obje cts: a(infinity)c(nu)(-1/3) . The micellar particle length is, however , unknown since its derivation depends intrinsically on the particle r adius R considered. A constant radius is found for the whole H-alpha d omain, and the electron density maps obtained from the x-ray diffracte d intensities are analyzed and allow determination of micellar radius (effective radius R(eff)=18.4+/-0.1 Angstrom, paraffin radius R(par)=1 6.7+/-0.1 Angstrom, and total radius R(tot)=20.5 Angstrom). From these values the resulting micellar size is between 170 and 640 Angstrom, w ith a value of 260 Angstrom for R(tot)=20.5 Angstrom.