Thermal behaviour of perfluoropolyether W/O percolative microemulsions

The thermal properties of a perfluoropolyether (PFPE) W/O microemulsion wer e investigated by Differential Scanning Calorimetry (DSC) both on freezing the liquid samples and upon their melting. PFPE systems as a function of in creasing volume fraction (Phi=water+surfactant/total), were studied along a dilution line with a water/surfactant molar ratio W/S=11. The percolative nature of these systems emerged directly from the spreading of the exotherm ic peaks associated with the freezing of the dispersed phase. This behaviou r was found to depend on whether the starting temperature of the DSC measur e was at, below or above the percolative threshold temperature of the given sample. A low temperature 'needle-like' peak was found around 143 K, immed iately after the glass transition due to the oil continuous phase. The low temperature peak was also present in other percolative, three-component mic roemulsions. The higher order phase transition at the percolation temperatu re was also evidenced.