Phase Behavior of Binary Mixture of Heptaethylene Glycol Decyl Ether and Water: Formation of Phase Compound in Solid Phase

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.

Phase Behavior of Aqueous Mixtures of Some Polyethylene Glycol Decyl Ethers Revealed by DSC and FT-IR Measurements

Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were used to investigate the phase behavior of aqueous binary mixtures of three polyoxyethylene type nonionic surfactants, penta-, hexa-, and octaethylene glycol decyl ethers (C10E5, C10E6, and C10E8, respectively) in the temperature range -40-70 degreesC. Many thermotropic transitions among various phases assumed by these mixture systems, including mesomorphic phases, were detected in DSC thermograms, from which the T-X phase diagrams were constructed with the aid of polarized optical microscopic observation to characterize the mesomorphic phases. It was revealed by FT-IR measurements that the phase compounds are formed in a solid phase between these surfactants and water molecules; the compositions of the compounds for the three surfactant species are expressed as C10E5 . 10H2O, C10E6 . 12H2O, and C10E8 . 16H2O, respectively. The stoichiometry of the phase compounds clearly demonstrates that just two water molecules are bound per oxyethylene unit of polyoxyethylene (POE) chain of the surfactants in the solid phase, probably due to the hydrogen bonding. It was also found that the phase state of the mixture is reflected in the wavenumber of the absorption maximum associated with the OH stretching vibration, nuOH, although no significant difference was appreciable in nuOH among mesomorphic phases. The nuOH decreased in the order L (liquid phase) > H1 (normal hexagonal phase) approximately V1 (normal cubic phase) approximately Lalpha (lamellar phase) > solid phase, which indicates that the hydrogen bonding between water and the POE chain of the surfactants becomes stronger in the sequence liquid < mesophase < solid. Copyright 1998 Academic Press.