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-cha in 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(PFH D), have been compared by using various techniques such as pyrene fluoresce nce spectroscopy, vapor pressure osmometry,'tensiometry, and dye solubiliza tion. The aggregational behavior of both systems in aqueous medium has been evidenced by the polarity decrease of the pyrene microenvironment with inc reasing surfactant concentration. The binding coefficient of pyrene with th e aggregates was calculated by application of the phase-separation model to the pyrene fluorescence results. The aggregation numbers of the HD (N-H) a nd PFHD (N-PF) micelles have been evaluated by application of the phase-sep aration and the mass-action law models to the osmotic coefficients measurem ents. The N-H value (26 +/- 8), which is in good accordance with previous e xperimental results (30 +/- 10), is higher than N-PF (15 +/- I). Both compo unds exhibit surface-active properties with a maximum surface tension lower ing of 42 and 57 mN m(-1) for HD and its perfluorinated homologous compound , respectively. Their solubilizing power toward Orange OT was compared. Cri tical 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 cha nges for micellization have been calculated.