X-ray diffraction study of the intermediate phases formed by sodium dodecylsulphate in aqueous mixtures of N-methylformamide

Abstract

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_α, is formed in the SDS/NMF system, the three sequences H_α ⇔ M_α ⇔ R_α, H_α ⇔ M_α ⇔ Q_α and H_α ⇔ Q_α (Ia3d) were observed with increase in concentration of NMF in the SDS/water/NMF mixtures. The sequences H_α ⇔Q_α and H_α ⇔ L_α 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_α → M_α → R_α to the H_α → M_α → Q_α sequences.