Determination of the critical concentration of micelle formation of polyoxyethylated alkylphenols in aqueous solutions by spectrophotometric method

The micellization of polyoxyethylated alkylphenols Triton X-100 (TX-100) and Triton X-114 (TX-114), which belong to nonionic surfactants, was studied in aqueous solutions using the spectrophotometric method. The spectral characteristics of the absorption curves of surfactant solutions were calculated in the concentration ranges: 0.02–0.80 mmol/L for TX-100 and 0.02-0.40 mmol/L for TX-114. The influence of the scanning step along the wavelength scale (0.1, 0.2, 0.5 and 1.0 nm) on the position of the maxima and absorption intensity was studied. It was found that the optical density increases monotonically over the entire concentration range. It was revealed that at all scanning steps there is a bathochromic shift in the absorption maximum of the long-wave band (275 nm) by 1.5 nm (TX-114) and 2.0 nm (TX-100) at a certain surfactant concentration. A characteristic kink is observed in the curve of the dependence of the position of the absorption maximum on the surfactant concentration, the position of which depends on the scanning step. A new method for the spectrophotometric determination of the CMC of TX-100 and TX-114 is proposed, based on establishing the dependence of the position of the absorption maximum of the long-wave band in the electronic absorption spectrum on the surfactant concentration in an aqueous solution. It was found that for graphical determination of CMC, the optimal scanning step is 0.1 nm. The CMC values for TX-100 and TX-114 were determined, which were (0.24 ± 0.02) mmol/L and (0.20 ± 0.01) mmol/L, respectively, consistent with the literature data.