Abstract
Preparation and analysis of sodium decylsulphate, as well as the elaboration of a ternay and a quaternary phase diagram are here presented. The lyomesophases were studied by: polarizing microscopy, small angle X-ray scattering, densimetry and refractometry. The results will be used as basis of comparison in subsequent articles for the related surfactants sodium decylphosphate and sodium decylsulphonate in lyotropic systems.