Transition from Competitive to Non-Competitive Solubilization with the Decrease in Number of Oxyethylene (OE) Units of Non-Ionic Surfactants towards Polycyclic Aromatic Hydrocarbons

• Published in: Bulletin of the Chemical Society of Japan 2019-01, Vol.92 (1), p.115-123
• Main Authors: Lone, Mohd Sajid, Chat, Oyais Ahmad, Vashishtha, Manu, Dar, Aijaz Ahmad
• Format: Article
• Language: English
• Subjects: Anisotropy; Competition; Hydrophobicity; Micelles; Naphthalene; NMR; Nuclear magnetic resonance; Polycyclic aromatic hydrocarbons; Solubilization; Spectrophotometry; Surfactants
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.20180215

This study investigates the effect of the number of oxyethylene (OE) groups on the solubilization and cosolubilization of two polycyclic aromatic hydrocarbons (PAHs) viz, naphthalene and pyrene in the conventional nonionic surfactants of the Brij series viz., Brij30, Brij56, Brij58 and Brij35 using various techniques like UV-visible spectrophotometry, spectrofluorometry, 1H NMR, and time resolved anisotropy measurements. In Brij56, Brij58 and Brij35 surfactant systems with relatively higher number of OE units, the micellar palisade layer is more hydrated than that of the Brij30 micelle which has only 4 OE groups constituting the palisade layer. Hence in these micellar systems the palisade layer being more hydrated is a less preferred choice for the hydrophobic compounds to reside. As a result of this, the two PAHs compete for the same hydrophobic core of the micelle which leads to the decrease in the solubilization of naphthalene as pyrene competes with it successfully because of its more hydrophobic character. In the case of Brij30, as the palisade layer of the micelle is less hydrated, naphthalene resides in the palisade layer whereas pyrene resides in the core because of its higher hydrophobicity. This leads to elimination of the competition between the two PAHs for the same solubilization site.