Articulo
Water-Induced Phase Transition in Cyclohexane/n-Hexanol/Triton X-100 Mixtures at a Molar Composition of 1/16/74 Studied by NMR
JOURNAL OF PHYSICAL CHEMISTRY B
Registro en:
1150899
1150899
Autor
Flores, Mario E
Martínez, Francisco
Olea, Andrés F
Shibue, Toshimichi
Sugimura, Natsuhiko
Nishide, Hiroyuki
Moreno-Villoslada, Ignacio
Institución
Resumen
Molecular aggregation in a mixture of Triton X100/n-hexanol/cyclohexane at a molar ratio of 1/16/74 is studied upon addition of small amounts of water. The composition of organic components has been chosen at a ratio n-hexanol/cyclohexane where a well-formed hydrogen bond network has been described. The ratio Triton X-100/nhexanol has been chosen to afford a stoichiometry of ethylene oxide (EO) residues/n-hexanol of 1/2. At these conditions the addition of water consecutively produces the appearance of three defined phases: a clear solution, a lamellar phase, and a microemulsion. The two corresponding transitions occur at water/EO/n-hexanol molar ratios of 2/1/2 (clear to lamella), and 3/1/2 (lamella to microemulsion), while phase separation occurs at a molar ratio of 4/1/2, highlighting the important role of stoichiometry. Molecular dynamics measured by H-1 NMR techniques, such as DOSY, and calculations of T-1, and T-2 relaxation times allow distinguishing the transition between the different phases and justifying their structure. Molecular assembly in the three phases is organized around hydrogen bond networks in which the hydroxyl groups of both TX-100 and n-hexanol, ethylene oxide groups of TX-100, and water participate. 1D H-1 NMR spectral changes correlate with the different characteristics of the different phases. As the main characteristics of the lamellar phase we find a very restricted mobility of the molecules involved, and water chemical shifts in 1D H-1 NMR spectra of around 5.0 ppm, higher than that of bulk water appearing at 4.7 ppm. Regular 2015 FONDECYT FONDECYT