Determination of critical micelle concentration (CMC) of nonionic surfactants by donor‐acceptor interaction with lodine and correlation of CMC with hydrophile‐lipophile balance and other parameters of the surfactants

Abstract The nonionic surfactants form donor‐acceptor complexes with iodine in aqueous medium. The spectral absorption and the shift in the λ max of l 2 upon complexation have been exploited to determine the critical micelle concentration (CMC) of Tweens, Brijs, and Triton X‐100. The CMC values obtained closely agree with those determined by other methods, including measurements of static surface tension, differential refractive index, and iodine solubilization. The spectral characteristics of the complex salt Kl 3 can be utilized as well to derive similar information. The CMC and the spectral shift can be correlated with the weight fraction of the polyoxyethylene groups and the hydrophile‐lipophile balance (HLB) in various ways, with the parameters in these relationships depending on the series to which the surfactant belong. Because both CMC and HLB depend on temperature, the results and the relations obtained are temperature‐dependent; those presented are with reference to 298 K.