Fluorocarbon and hydrocarbon short-chain nonionic amphiphiles: A comparative study of their behavior in aqueous medium

The aqueous solution properties and the micellar structure of two short-chain nonionic surfactants containing a hydrocarbon tail, 1,2-hexanediol (HD), and a perfluorinated tail, 3,3,4,4,5,5,6,6,6-nonafluoro-1,2-hexanediol(PFHD), have been compared by using various techniques such as pyrene fluorescence spectroscopy, vapor pressure osmometry,'tensiometry, and dye solubilization. The aggregational behavior of both systems in aqueous medium has been evidenced by the polarity decrease of the pyrene microenvironment with increasing surfactant concentration. The binding coefficient of pyrene with the aggregates was calculated by application of the phase-separation model to the pyrene fluorescence results. The aggregation numbers of the HD (N-H) and PFHD (N-PF) micelles have been evaluated by application of the phase-separation and the mass-action law models to the osmotic coefficients measurements. The N-H value (26 +/- 8), which is in good accordance with previous experimental results (30 +/- 10), is higher than N-PF (15 +/- I). Both compounds exhibit surface-active properties with a maximum surface tension lowering of 42 and 57 mN m(-1) for HD and its perfluorinated homologous compound, respectively. Their solubilizing power toward Orange OT was compared. Critical micelle concentrations (CMCs) have been determined in the temperature range 20-50 degrees C (30-50 degrees C for PFHD insoluble below 30 degrees C), and thermodynamic parameters such as standard enthalpy and entropy changes for micellization have been calculated.