title: Near-infrared spectroscopic study of a water-in-supercritical CO2 microemulsion as a function of the water content.
abstract: A water-in-supercritical CO(2) microemulsion is a reverse micelle encapsulating a nanometer-size water droplet dispersed in supercritical CO(2). In the microemulsion solution, water exists not only in the reverse micelle but also in the solvent CO(2). For quantitative analysis of the water distribution, near-infrared spectra of water + CO(2) and water + surfactant + CO(2) mixtures were measured over a wide range of water/CO(2) ratios from 0.1 to 1.0 wt% at 60 °C and 30.0 MPa. The stretching combination band of water was decomposed into two components, a sharp one peaked at 7194 cm(-1) assigned to monomeric water dissolved in CO(2) and a broad one around 7000 cm(-1) corresponding to aggregated water in the microemulsion. Integrated molar absorptivities of these types of water were negligibly different from each other, despite the different hydrogen-bonding environments. The spectral decomposition revealed that water is distributed mainly into CO(2) at water contents smaller than 0.5 wt% and then is introduced into the microemulsion after saturation of water in CO(2) and full hydration of the surfactant headgroup.
authors.affiliation: Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan. chikulin@ni.aist.go.jp
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Takebayashi
authors.forename: Masanobu
authors.initials: M
authors.lastname: Sagisaka
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Sue
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoda
authors.forename: Yukiya
authors.initials: Y
authors.lastname: Hakuta
authors.forename: Takeshi
authors.initials: T
authors.lastname: Furuya
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry*; D006860:Hydrogen Bonding; D019265:Spectroscopy, Near-Infrared; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D004655:Emulsions; D013501:Surface-Active Agents; D014867:Water; D002245:Carbon Dioxide