Use of stepwise regression analysis and cluster analysis for the study of the interaction between nonionic surfactants

The interaction of 18 nonionic surfactants (9 nonylphenylethyleneoxide oligomers, containing in average 5, 6, 8, 9, 10, 11, 15, 23 and 30 ethyleneoxide groups per molecule, and 9 tributylphenylethyleneoxide oligomers, containing in average 4, 6, 8, 10, 11, 13, 18, 30 and 50 ethyleneoxide groups per molecule) with ethoxylated stearic acid (average ethyleneoxide number 50, Myrj53) was studied by reversed-phase chromatography, and the relative strength of interaction was calculated separately for each nonionic surfactant–Myrj53 pair. Stepwise regression analysis and cluster analysis were used for the determination of the relationship between the strength of interaction and the molecular substructures and physicochemical parameters of surfactants. Calculations indicated that the hydrophobicity, specific hydrophobic surface area of surfactants and their capacity to interact with Myrj53 depended negligibly on the presence of salt, and the hydrophobicity of surfactants has the highest impact on their binding to Myrj53 suggesting the involvement of hydrophobic forces in the interaction.