Cloud point property was found in the aqueous mixtures of sodium dodecyl sulfate（SDS）and cetyl trimethyl ammonium bromide（CTAB）and the cloud point area in pseudo ternary plase diagram of SDS/CTAB/Na2SO4/H2O was studied.It was found that the cloud point area was the aqueous two-phase system area,in which the containing of SDS was more than that of CTAB.The cloud point area would enlarge when the temperature was high and the length of cationic surfactant carbochain had some effect on the position of cloud point area.
The effect of alcohol on the aqueous two-phase system properties of SDS/CTAB/H 2O/Na 2SO 4 system was studied by the pseudo ternary phase diagram. The electrostatic forces (both attraction and repulsion) between cationic surfactant and anionic surfactant decreased because of the interaction of alcohol hydroxyl group and surfactant polar group. As a result, the phase area width of aqueous two-phase system increased. Long chain alcohol (more than five carbonatoms), which was in high concentration in the SDS/CTAB/H 2O/Na 2SO 4 system, caused the anionic aqueous two-phase system area to vanish and the cationic aqueous two-phase system area to become wider. The CTAB rich phase turned from top phase to bottom phase.
