This work reports the study of surface and aggregation properties of formulations containing mixed niosomes of the non-ionic surfactant sorbitan monooleate (Span 80) and the cationic surfactant cetyltrimethylammonium bromide (CTAB), in concentrations of 20 and 4 mol/m3, respectively, in salt-free water and in the presence of NaCl (20, 50 and 80 mol/m3). The aim of this work was the formulation of stable Span 80 and CTAB mixed niosomes with low surfactant concentration. The mixed niosomes were prepared by ultrasonication and their properties (surface tension, particle size distribution, ζ-potential, stability over time and morphology) were measured using different techniques. Data were analyzed and compared with those of the individual surfactants. Experimental results show that the addition of salt decreased the critical micelle concentration (CMC) and the surface tension of the surfactant dispersions with relation to their free-salt formulations. The presence of CTAB in the mixed niosome bilayer decreased the particle size and increased the stability of the mixed niosomes in all the formulations studied, compared with those of single Span 80. Synergism between both surfactants was obtained in the formation of niosome bilayers for formulations in pure water and with 20 and 50 mol/m3 of salt, while antagonism was observed in that of 80 mol/m3 NaCl. These results may allow the use of CTAB adsorbed on mixed niosomes in industrial applications, taking advantage of its antiseptic and antibacterial properties and solving the limitation imposed by its high Krafft temperature.
