where CM1b is the CMC of the individual surfactant 1b (CTAB). The calculated values of TX-100 and CTAB mole fractions in the mixed micelle indicate that the composition of the micelles is close to that in the bulk phase if ˛ = 0.8. In other cases, the composition of the TX-100 and CTAB mixture is different and the CTAB mole fraction in the mixed micelle is considerably lower than that in the bulk phase. It is interesting that the content of CTAB in the micelles increases with the increase of ethanol concentration from 0 to 1.07 M (Figs.S11 and S12). Above this concentration it is almost constant. It is probably connected with different behavior of ethanol at its low and high concentrations. In the range of ethanol concentration from 0to 1.07 M, it changes the CMC probably by the adsorption mainly in the outer portion of the micelle close to the water–micelle interface [1]. Above this concentration, ethanol changes CMC rather by modifying the interaction of water with the surfactant molecules or with the micelle. It results from the modification of the water structure, its dielectric constant and the solubility parameter. From the comparison of the mole fraction of CTAB in the mixed micelle to that in the mixed mono layer at the solution air interface, it can be stated that the tendency of CTAB to adsorb at the water air interface is lower than the tendency to form mixed micelle with TX-100. Introducing the values of XM1a to Eq. (4), the ˇM parameter was determined. The ˇM parameter assumes a negative value for all the solutions studied (Fig. S13). The lowest values of ˇM were obtained for the TX-100 and CTAB mixture at ˛ = 0.8, at which the biggest synergetic effect in the micelle formation takes place. Comparing ˇM for the mixed micelle formation to that for the mixed mono layer formation at the solution air interface we can state that the synergetic effect is higher for the micelle formation than for the surface tension reduction.