Characterization of the Nanostructures in Liquid Crystalline Mesophases Present in the Ternary System Brij-35/Dibutyl Ether/H2O by Small- and Wide-Angle X-ray Scattering

Abstract

We investigated the liquid crystalline phase structures and their temperature-dependent dynamics in the ternary system composed of Brij-35 [poly(oxyethylene(∼23))lauryl ether, C12OE∼23], dibutyl ether (DBE) and 10 mM Na/K buffer. A sequence of schematic ternary phase diagrams at 10, 20, 30, 40, and 60 °C, derived from temperature-scanning small- and wide-angle X-ray scattering (SWAX), has been established. In the binary Brij-35/H2O system, the amphiphilic component Brij-35, being totally miscible with water, self-assembles as a function of its concentration into a normal micellar solution L1, a normal packed micellar cubic I1-phase region, and an extended region of various lamellar structures. The cubic I1 phases show diffraction patterns with Im3m (unit cell parameter aIm3m = 85−94 Å) and Ia3d (aIa3d = 162−167 Å) symmetry. Increasing temperature destabilizes the cubic phases between 15 and 55 °C, depending on the weight ratio of the used components. The lamellar phases show unit cell dimensions of a = 179−181 Å. A phase transition from Lc (crystalline lamellar phase), Lβ (gel lamellar phase), to a isotropic micellar phase, here denoted as L2, occurs at temperatures from 15 to 35 °C, as a function of the water content. The DBE uptake of these structures is limited to 20−50%(w/w), which generates biphasic regions at higher DBE amounts, where a DBE excess phase containing approximately 2% (w/w) H2O and 0.02% (w/w) Brij-35 is formed. Increasing amounts of DBE leadwith exception of the Lc phaseto enhanced phase temperature stabilities in the water-lean region and induce normal hexagonal H1 (a = 68−135 Å) and various cubic structures. We found the cubic space groups Im3m and Ia3d with unit cell dimensions aIm3m = 83−112 Å and aIa3d = 162−195 Å in the cubic I1 region and Pn3m (aPn3m = 164 Å) and Ia3d (aIa3d = 187−214 Å) as well as Fd3m (aFd3m = 218−275 Å) in the cubic region with low water contents.