Thermodynamic investigation of the micellization and the adsorption of short perfluoroalkylated diols via fluorescence spectroscopy and tensiometry

The micellization and adsorption of two short chain perfluorodiols 3,3,4,4, 5,5,6,6,6-nonafluorohexane-1,2-diol (nFHD) and 3,3,4,4,5,5,6,6,7,7,8,8,8-tr idecafluorooctane-1,2-diol (tFOD) are examined from a thermodynamic point o f view as a function of temperature and methanol content. The microenvironm ent of the fluorinated aggregates is evaluated by the fluorescence probe me thod using pyrene and a molecular rotor 1,1-dicyano-4-(p-dimethylaminopheny l)-1,3-butadiene (DMAPhC). The formation of micellar aggregates being evide nced, the results are discussed in terms of the polarity and of the cohesio n behavior of the micellar aggregates by taking into account the methanol ( MeOH) effect. The critical micellization concentrations thus determined are compared with those given by surface tension measurements. Micellar and ad sorption thermodynamic parameters such as Gibbs free energies, enthalpies, and entropies are determined together with the surface areas. The results a re compared with literature data and discussed. A model for describing the adsorption process of the fluorinated compounds upon the influence of metha nol is finally proposed. (C) 2001 Academic Press.