A review of recent studies on aqueous binary mixed surfactant systems

Recent studies on mixed surfactant systems were systematically overviewed, paying special attention to synergism observed in micellization as well as adsorbed film formation upon mixing of a few nonionic surfactants with a variety of surfactants (such as anionics including bile salts and a hybrid type surfactant, cationics including a Gemini type surfactant, different types of nonionics and a zwitterionic surfactant used as a membrane solubilizer) in addition to various combinations of anionics. Through the text, it was shown for each given binary mixed system composed of surfactants 1 and 2 how to estimate not only the composition of mixed micelles (Y(2)) equilibrated with singly dispersed surfactant species in bulk solution phase, where the mole fraction of 2 in the surfactant mixture is denoted as X(2), but also the composition of adsorbed film phase (Z(2)). Almost all combinations were discussed in terms of the respective interaction parameters, omega(R) and omega(A), in mixed micelles (3-D phase) and in mixed adsorbed film (2-D phase), respectively, surface excess concentration (Gamma), partial molecular area (PMA), minimum surface Gibbs energy (G(s)min), and such defined measures as pC(20), CMC/C(20) etc. for evaluation of synergism.