title: Nonionic reverse micelles near the critical point.
abstract: We report shape, size, and internal cross-sectional structure of diglycerol monomyristate (C₁₄G₂) reverse micelles in n-hexadecane near the critical point using small-angle X-ray scattering (SAXS). Pair-distance distribution function, p(r), which gives structural information in real-space, was obtained by indirect Fourier transformation (IFT) method. The p(r) showed a clear picture of rodlike micelles at higher temperatures well above the critical point (micellar solution phase separates into two immiscible liquids at ~ 48°C). At a fixed surfactant concentration (5% C₁₄G₂), decrease in temperature increases the micellar size monotonously and surprisingly shape of the p(r) curve at 50°C; close to the critical point, mimics the shape of the two dimensional disk-like micelles indicating the onset of critical fluctuations (attractive interactions among rodlike micelles forming a weak network). A similar behavior has been observed with normal micelles in aqueous system near the critical point. When the system is heated to 60°C, shape of the p(r) curve regains rodlike structure. At fixed temperature of 60°C, increase in C₁₄G₂ concentration induced one dimensional micellar growth. Maximum length of micelles increases from ca. 23.5 to 46.0 nm upon increasing concentration from 1 to 12% keeping cross section diameter apparently unchanged at ca. 4.0 nm.
authors.affiliation: International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS).
authors.forename: Lok Kumar
authors.initials: LK
authors.lastname: Shrestha
authors.forename: Rekha Goswami
authors.initials: RG
authors.lastname: Shrestha
mesh_terms: D005995:Glyceryl Ethers / Q000737:chemistry*; D008823:Micelles; D015394:Molecular Structure; D050178:Monoglycerides / Q000737:chemistry*; D012997:Solvents; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature
chemical_list: D005995:Glyceryl Ethers; D008823:Micelles; D050178:Monoglycerides; D012997:Solvents; D013501:Surface-Active Agents