Low-temperature phase behaviour of the binary system water–oxyethylated glycerol of polymerization degree n = 5 and intermolecular interactions in the system

Abstract

In this paper, phase and glass transitions occurring in a binary system water–oxyethylated glycerol of polymerization degree n = 5 (OEG n =5) are studied by differential scanning calorimetry (DSC) in the concentration range 0–100% (w/w) at temperatures lower than 273 K. The supplemented phase diagram of this system has been constructed for the first time. Concentration and temperature regions for the existence of a completely amorphous state and a heterogeneous crystalline/amorphous state have been determined. Processes of formation of crystalline and amorphous phases in the water–OEG n =5 system are studied by optical cryomicroscopy, both during cooling and subsequent heating. The cryomicroscopic data confirm the conclusions derived from the DSC data analysis. The number of strongly and weakly bound water molecules per OEG n =5 molecule has been calculated on the basis of the analysis of the supplemented phase diagram of the water–OEG n =5 system. The hydration number of an OEG n =5 molecule has been also determined by infrared spectroscopy.