Based on the application research of aqueous two-phase system, this paper firstly studied the aqueous two-phase system of traditional anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant with opposite charges, including traditional cationic surfactant dodecyl trimethyl ammonium bromide and coupled cationic surfactant (12-3- 12, C 120H and c1). The results show that under appropriate conditions, coupled cationic surfactants-12-3- 12, C 120H and C 140H are similar to traditional cationic surfactants, and can be mixed with anionic surfactants (SDS) to form a balanced aqueous two-phase system. However, the properties of aqueous two-phase system are quite different from those of traditional surfactant aqueous two-phase system. The aqueous two-phase region in the system is a single cationic surfactant aqueous two-phase region, and the mixing ratio of the two surfactants in the phase region basically changes linearly with the change of solution concentration. The phase formation time of aqueous two-phase in this mixed system is long, and it changes with the change of solution concentration and mixing ratio. The minimum concentration of surfactant forming aqueous two-phase system is related to the critical micelle concentration of mixed system. The higher the critical micelle concentration, the higher the minimum concentration of surfactant for forming aqueous two-phase system. For the surfactant mixed system with strong hydrophobicity, due to the strong interaction between them, milky white gel or even white precipitate appears, resulting in the loss of aqueous two phases. The aqueous two-phase system can be obtained by increasing the system temperature.

On this basis, taking CTAB/SDS/H20 and Gemini/SDS/H20 as the research objects, the effect of polymer PEG on the aqueous two-phase properties of surfactants was discussed. The results show that the addition of polymer PEG can not only change the properties of solvent, but also affect the interaction between cationic and anionic surfactants, thus affecting the distribution of aqueous two-phase region. In addition, the addition of polymer PEG greatly improves the viscosity of the solution, which leads to the slow movement of various aggregates in the solution and a relatively long time to reach equilibrium, and finally prolongs the phase formation time of the aqueous two-phase system.

When investigating the influence of salt on the properties of polymer/surfactant aqueous two-phase system (Gemini( 12-3- 12, 2Br-)/SDS/PEG), it is found that salt has 12-3- 12, 2br-/SDS. Firstly, it is reflected in the expansion of protocation aqueous two-phase zone (ATPS-C) (the minimum total concentration of surfactant forming aqueous two-phase decreases, and the ratio range of two surfactants widens), and tends to move in the direction of increasing the content of cationic coupling surfactant, and the degree of widening and the moving range are related to the size of anion radius; Secondly, a new aqueous two-phase region (ATPS-A) appeared, that is, the addition of salt made the original anionic aqueous two-phase region appear. The addition of salt greatly shortens the time to form the aqueous two-phase and the time required for the aqueous two-phase to reach equilibrium. Compared with the salt-free system, the salt-containing aqueous two-phase system has stronger extraction effect.

The study on the properties of the mixed system of ionic liquids and surfactants shows that ionic liquids C6[MIM]Br and C8[MIM]Br are similar to coin-type ionic surfactants, and can also form aqueous two-phase with the traditional anionic surfactant SDS mixed solution under appropriate conditions. With the change of carbon chain in ionic liquids, the properties of mixed solutions show obvious differences. The chain length of substituted alkyl groups in ionic liquids is an important factor affecting the formation of aqueous two-phase system. When the carbon number of alkyl substituents is greater than or equal to 6, an aqueous two-phase system will be formed.

Special composite ionic liquid (C8[mim]Br)/ coupled anionic surfactant (c12h25ooocch2 (coona)-CH2 (coona) coocl2h25.2br/water can also form an aqueous two-phase system under certain conditions, and the properties of this aqueous two-phase system are similar to those of traditional cationic and anionic surfactants. These studies are of great significance to theoretical development and practical application.

In addition, the phase diagram and some basic properties of isopropanol-ammonium sulfate mixed aqueous solution were also studied, which provided basic data for its further application in extraction and separation.