CHARACTERIZATION OF STRUCTURAL TRANSITIONS IN THE SLS DECANOL/WATER SYSTEM/

The ternary system sodium-dodecylsulphate (SLS)/decanol/water has been investigated at three different water contents and varying ratios of cosurfactant to surfactant by means of polarized optical microscopy, H -2-NMR quadrupole splittings and small angle x-ray scattering. Upon ad dition of decanol a hexagonal phase transforms into a lamellar phase. For the highest water content of 0.65 no intermediate two-phase region s are detected but nematic phases are formed between. The lamellar pha se at low cosurfactant content is very sensitive to changes of tempera ture and seems to be a so-called defective one with curved interfaces. From the scaling behavior it is concluded that the building units see m to be ribbons of increasing width on addition of cosurfactant or amp hiphilic substance. By reaching a decanol mole fraction of 0.4 a ''cla ssical'' lamellar phase with well-known behavior is formed. During the se transformations the position of the first diffraction maximum chang es gradually irrespective of phase transitions. The maximum mole fract ion of cosurfactant the lamellar phase of our system can incorporate i s 0.77.