Solid-Liquid Phase Behavior of Binary Mixture of Tetraethylene Glycol Decyl Ether and Water

Solid-liquid phase behavior of binary mixture of nonionic surfactant, tetraethylene glycol decyl ether (C10E4), and water was examined by means of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), and visual observation in the temperature range -40-70 degreesC. The DSC experiments allowed us to determine many phase boundaries among various phases appearing in this mixture system, including mesomorphic phases. The T-X phase diagram for fluid phases of C10E4/H2O mixture constructed from the results of DSC and visual observation was in good agreement with that previously reported by Lang and Morgan for the same mixture system except for the occurrence of a dilute lamellar phase (Lang, J. C. and Morgan, R. D., J. Chem. Phys., 73, 5849 (1980). The FT-IR spectra obtained for the mixture in a solid state demonstrated that the phase compound expressed by C10E4 . 6H2O is formed in the solid phase, which indicates that there is a strong interaction in the solid state between water and the hydrophilic polyoxyethylene chain of the surfactant. The FT-IR results also suggested that the strength of the hydrogen bond between water and the polyoxyethylene chain of C10E4 differs among the phase states of the mixture, and increases in the order L2 < L1 < Lalpha approximately H1 < solid, where L2 refers to the inverted micellar phase, L1 the normal micellar phase, Lalpha the lamellar phase, and H1 the normal hexagonal phase. Copyright 1998 Academic Press.