X-RAY-DIFFRACTION STUDY OF THE INTERMEDIATE PHASES FORMED BY SODIUM DODECYL-SULFATE IN AQUEOUS MIXTURES OF N-METHYLFORMAMIDE

We report the sequence of intermediate phases formed by sodium dodecylsulphate (SDS) in water on addition of N-methylformamide (NMF). Although only a single phase, L(alpha), is formed in the SDS/NMF system, the three sequences H(alpha) double-line arrow pointing left and right M(alpha) double-line arrow pointing left and right R(alpha), H(alpha) double-line arrow pointing left and right M(alpha) double-line arrow pointing left and right Q(alpha) and H(alpha) double-line arrow pointing left and right Q(alpha) N(Ia3d) were observed with increase in concentration of NMF in the SDS/water/NMF mixtures. The sequences H(alpha) double-line arrow pointing left and right Q(alpha) and H(alpha) double-line arrow pointing left and right L(alpha) were identified in the water/NMF mixture, although they were not observed in the initial SDS/water system or in the SDS/NMF system. These results indicate that solvent mixtures could be profitably employed to investigate the conditions of formation of intermediate phases and to study the transitions of the H(alpha) --> M(alpha) --> R(alpha) to the H(alpha) --> Q(alpha) sequences.