Aggregation Behaviors and Interfacial Properties of Oxyethylated Nonionic Surfactants

Abstract

Four nonionic surfactants C₁₆E_n with varying EO number were synthesized. The characteristics of this series of nonionic surfactants, including surface tension, critical micelle concentration (CMC), interfacial activity, and surface pressure, were presented. The surface tension data indicated that γ_CMC increased with hydrophilic PEO chain length while CMC decreased. The area per surfactant molecule at the air/water interface increased as PEO chain length increased. The probe, pyrene, was employed to investigate nonionic micelles of varying EO number in steady‐state fluorescence. The CMC, obtained from the I₃/I₁ ratio, agreed well with the results of the surface tension experiment. The interfacial properties were studied by using a heptane‐toluene/water model system. We found that interfacial activities increased with the degree of ethoxylation because of their hydrophile‐lipophile balance. From the π–A isotherm, it can be deduced that C₁₆E_n nonionic surfactants had excellent molecular flexibility. The surface pressure data also showed that this kind of surfactant with longer PEO chains occupied a larger area per molecule at the interface.

Keywords:

• Nonionic surfactant
• aggregation behavior
• surface tension
• interfacial activity
• fluorescence
• surface pressure

Acknowledgment

The authors gratefully acknowledge the financial support of Key Technologies R & D Programme (02BA312B07).