PHASE-BEHAVIOR OF BINARY MIXTURE OF HEPTAETHYLENE GLYCOL DECYL ETHER AND WATER - FORMATION OF PHASE COMPOUND IN SOLID-PHASE

Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were used to construct and characterize the phas e diagram for a binary mixture of heptaethylene glycol decyl ether (C1 0E7) and water in the temperature range from -60 to 80 degrees C. Plot s of the endothermic peak temperatures obtained by DSC measurements ag ainst compositions provided eutectic solid-liquid phase boundaries wit h a eutectic composition of 34 wt% of H2O. On the other hand, heat of fusion per unit weight of the mixture changed discretely at the compos ition corresponding to the ''eutectic'' composition. Furthermore, the IR spectra obtained for the mixture in the solid phase were well repro duced as a superposition of those for the mixture of 34 wt% H2O and pu re components but were not reproduced by superimposing the spectra obt ained for the solid surfactant and ice. These observations indicate th at a solid phase compound is formed between C10E7 and water with a sto ichiometry of 1:14 and that the compound and pure components exist as separate phases, rather than the phases separating into surfactant and ice, which would be expected if the C10E7/water mixture formed a true eutectic mixture system. It is estimated from the composition corresp onding to the phase compounds that two molecules of water per oxyethyl ene unit are bound to hydrophilic polyoxyethylene chain of C10E7 to fo rm a hydrated compound. (C) 1997 Academic Press.