PHASE-SEPARATION OF THE AQUEOUS-SOLUTION AND THE SURFACE-ACTIVITY OF OXYETHYLENATED CATIONIC ANIONIC SURFACTANTS

The phase separation of the aqueous solutions of cationic-anionic surfactants, C8H17 (OC2H4)(n)SO4Na-C8H17N(CH3)(3)Br (C(8)E(n)S-C(8)NM(3): n = 0, 1, 3), C8S-C8H17 (OC2H4)(3)N(CH3)(3)Cl (C(8)E(3)NM(3)), C(8)E(3)S-CmH2m+1N(CH3)3Br (C(m)NM(3); m = 10, 12), C12H25(OC2H4)(n)SO4Na-C12H25N(CH3)3Br (C(12)E(n)S-C(12)NM(3): n = 0, 3, 5, 7) and C8H17C6H4 (OC2H4)(9.8)SO4Na(C-8 Phi E(9.8)S)-C(m)NM(3) (m = 12, 14, 16) has been investigated. The concentration region of phase separation (CRPS) of the aqueous solution of C(8)E(n)S-C(8)NM(3) and C(12)E(n)S-C(12)NM(3) contracts with the increase in n, and the CRPS disappears when n is equal to (or over 3) for C(8)E(n)S-C(8)NM(3) and 7 for C(12)E(n)S-C(12)NM(3). On the contrary, the CRPS of the aqueous solution of C(8)E(8)S-C(m)NM(3), increases with the increase in m. The comparison between the molecular interaction parameter and the CRPS of the mixed system shows that the greater the molecular interaction between the two surfactant components, the easier it is for phase separation to occur, and vice versa. In the C-8 Phi E(9.8)S-C(m)NM(3) system, there is no phase separation even if m is very large. The surface activity of a 1:1 C-8 Phi E(9.8)S-C(m)NM(3) mixture is still much higher than that of the single components. A relatively large number of oxyethylene (EO) groups introduced into the cationic-anionic surfactant molecule makes the mixed aqueous solution homogeneous at a very high concentration, which is of great significance in theory and practice.