Spectrophotometric Determination of the Critical Micelle Concentrations of Polyoxyethylated Alkylphenols in Aqueous Solutions

Abstract

A spectrophotometric method has been employed to study micellization of nonionic surfactants (NSs), namely, polyoxyethylated alkylphenols, Triton X-100 (TX-100) and Triton X-114 (TX-114), in aqueous solutions. The spectral characteristics have been calculated for the curves of light absorption by surfactant solutions in concentration ranges of 0.02–0.80 and 0.02–0.40 mmol/L for TX-100 and TX-114, respectively. The influence of the steps of scanning along the wavelength scale (0.1, 0.2, 0.5, and 1.0 nm) on the positions of the maxima and the intensities of the absorption has been studied. The optical density has been found to increase monotonically throughout the concentration range. It has been revealed that, at all scanning steps, a bathochromic shift is observed for the absorption maximum of the long-wavelength band (275 nm) by 1.5 and 2.0 nm for TX-114 and TX-100, respectively, at certain NS concentrations. The curve for the dependence of absorption maximum position on NS concentration exhibits a characteristic inflection, whose position depends on the scanning step. A new method has been proposed for the spectrophotometric determination of the critical micelle concentrations (CMCs) of TX-100 and TX-114 from the dependence of the position of the absorption maximum of the long-wavelength band in the electronic absorption spectrum on the surfactant concentration in an aqueous solution. It has been found that a scanning step of 0.1 nm is optimal for the graphical determination of CMC. The CMC values have been determined for TX-100 and TX-114. The obtained values have appeared to be consistent with the literature data and equal to (0.24 ± 0.02) and (0.20 ± 0.01) mmol/L, respectively.