The lamellar phase of the sodium dodecylsulfate/decanol/toluene/formamide system: NMR and phase studies of solubilization

The phase behavior of the system sodium dodecylsulfate/decanol/toluene/ formamide was investigated and pseudo-ternary diagrams established. In particular, the effect of varying the amount of toluene in the system on the stability of the lamellar phase region was studied in detail. Deuterium NMR and low-angle x-ray diffraction measurements showed that more toluene was distributed between the surfactant chains as the amount of decanol in the system is reduced, resulting in a more disordered dynamic structure in the bilayers. Similarly, increased formamide content lead to greater penetration of the toluene into the bilayer and more disorder. Both factors were found to be instrumental in decreasing the stability of the lamellar structure.