On the Head Group Effect on Critical Micelle Concentration of Cationic Surfactants Using Molecular Connectivity Indices and Atomic Partial Charges

Abstract

The influence of the head group structure on the critical micelle concentration of cationic surfactants, mainly quaternary ammonium bromide salts with one alkyl tail, has been studied theoretically by QSPR using molecular connectivity indices and also the atomic partial charges. Two models obtained allow to study the effect of head group structure modification on the value of the critical micelle concentration. The model, which contains molecular connectivity indices together with the charge localized on the central nitrogen atom, has a wider descriptive capability than the model which contains topological indices only. The present semi-empirical charge investigations of different quaternary ammonium salts show that the charges of the quaternary ammonium head groups are approximately the same, but one of the obtained models shows that the significant part of that charge, which is localized on the central nitrogen atom, affects the value of the critical micelle concentration.

On the hydrophobic chains effect on critical micelle concentration of cationic gemini surfactants using molecular connectivity indices

“…Among the factors known to affect the cmc value in aqueous solution is the structure of the surfactant [1]. Therefore, as shown in many articles [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], the critical micelle concentration can be predicted directly from the structure of the molecule by quantitative structure-property relationship analysis, in short QSPR. The first correlation was given by Klevens [19] who empirically found that the logarithm of cmc linearly decreases with the increase in the number of carbon atoms in the surfactant alkyl chain.…”