Application of Octanol/Water Partition Coefficients in Surfactant Science: A Quantitative Structure−Property Relationship for Micellization of Anionic Surfactants

The octanol/water partition coefficient, usually as its logarithm, log P, is widely used as a hydrophobicity parameter in modeling pharmacological and toxicological properties. Since log P values can be calculated from molecular structure by summation of fragment values, they are very useful in predicting various biological properties of chemicals. Although hydrophobicity is a key concept in surfactant science, to date log P has not found much application in this field. In this paper, a log P based quantitative structure−property relationship (QSPR) is derived for anionic surfactant micellization potential, quantified as pCMC, the negative logarithm of the critical micelle concentration. The micellization potential of anionic surfactants covering a diverse range of structures is found to be well modeled by a combination of two parameters, πh and L, the former being the log P fragment value for the hydrophobe (simply defined as the whole molecule minus the negatively charged fundamental fragment) and the l...