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 ± 1). 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 °C (30−50 °C for
PFHD insoluble below 30 °C), and thermodynamic parameters such as standard enthalpy and entropy changes
for micellization have been calculated.
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