Aggregation behaviors and interfacial properties of oxyethylated nonionic surfactants

Four nonionic surfactants C16En 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 gamma(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 I-3/I-1 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 pi-A isotherm, it can be deduced that CIA, 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.