Partition coefficients of nonionic surfactants in water/n-alkane systems

In water/oil systems, surfactants partition between the water phase and the oil phase according to their solubility in both phases. The ratio between the concentration of the surfactant in the oil phase and in the water phase at equilibrium is known as the partition or distribution coefficient (Kp). The partition coefficient (Kp) is an important fundamental parameter essential to understanding and controlling phenomena in water–oil-surfactant systems under both equilibrium and non-equilibrium conditions. In the present work we report on the partitioning of three different classes of nonionic surfactants in the pre-cmc regime, namely polyoxyethylene alkyl ethers (CiEj), alkyl dimethyl phosphine oxides (CnDMPO) and alkyl glycosides (β-CnGm) between water and different n-alkanes. We focus on the influence of the surfactant’s molecular structure (alkyl chain length, head group size and type), and oil chain length on Kp to derive systematic structure–property relationships. Moreover, we discuss the influence of the surfactant purity on partition coefficients of technical grade alkyl glycosides and polyoxyethylene alkyl ethers, respectively.

This study presents the determination of and the discussion over the water/n-alkane partition coefficients Kp of nonionic surfactants for various n-alkanes, namely n-hexane, n-octane, n-decane and n-dodecane.Figure optionsDownload high-quality image (71 K)Download as PowerPoint slideResearch highlights
► Partition coefficients Kp of nonionic surfactants increase with increasing alkyl chain length of the surfactant.
► Kp of nonionic surfactants increases with decreasing chain length of the n-alkane.
► Kp of nonionic surfactants in water/n-alkane were found to increase in the order β-CnGm<► For technical and pure surfactants similar trends for Kp but different equilibration times were observed..