Structure and Morphology of the Intermediate Phase Region in the Nonionic Surfactant C₁₆EO₆/Water System

Abstract

The concentration interval of 48−62 wt % hexaethylene glycol n-hexadecyl ether (C16EO6) in deuterium oxide (2H2O) has been investigated using optical microscopy, 2H nuclear magnetic resonance, and small angle X-ray scattering and the detailed phase behavior established. On cooling from the lamellar phase (Lα), the phase sequence defected lamellar (Lα H), mesh intermediate (Int.), Ia3d cubic (V1), and hexagonal (H1) or hexagonal plus gel biphase (H1 + Lβ) was observed. On heating from the hexagonal or two-phase region, the region of intermediate and cubic phases formed on cooling is replaced by an Ia3d cubic phase. The mesh intermediate phase, formed on cooling, is demonstrated to have a rhombohedral structure, assigned the space group R3̄m. It represents a phase in which the water-filled defects of the higher temperature Lα H phase become correlated between layers. The formation of the phase is driven by the need to introduce more curvature into the interface as the temperature is decreased because of increased ethylene oxide head group (EO) hydration. The interlayer correlation arises from the strong, repulsive head group overlap interaction in this system.

Segmental order parameters in a nonionic surfactant lamellar phase studied with 1H–13C solid-state NMR

“…3) have minor deviations with respect to the long axis direction of the molecule, then one can think of the C a coupling magnitude as a measure of the lamella curvature. In fact, this assumption, combined with results obtained using other techniques, 22 has been the basis of a large number of 2 H NMR studies, 6,9,36 where the maximum of the C a quadrupolar coupling as function of temperature was interpreted as the transition of the lamellar phase, L a , to a porous lamellar phase, L H a . As the curvature is related to the degree of hydration, then the C a splitting is mainly dependent on the fraction of hydrated EO units.…”

“…Temperature-dependent transitions from classical lamellar phases to random mesh phases or ''porous'' lamellar phases have been shown to exist in numerous studies. 6,9,22 It has been argued that the fluctuations of order parameters with temperature in nonionic surfactant mixtures can be interpreted as a measure of perforation density. In this paper we interpret the temperature dependence of the dipolar couplings from a simple conformational basis.…”

Phase Behavior and Effect of Enantiomerism on Potassium N -Dodecanoyl Alaninate/Water/Decanol Systems

“…There are several reports (39) of defected or disrupted lamellar (L a H ) phase in surfactant-water binary systems of ionic surfactants, viz., sodium dodecyl sulphate (40), lithium perfluorooctanoate (41) and cesium pentadecafluorooctanoate (37,42), and long-chain poly (oxyethylene) surfactants (36,(43)(44)(45)(46). However, we are not aware of any report of the L a H phase between the H 1 or R 1 and the L a phase in ternary systems, except that reported by Kekicheff et al in the SDS/water/decanol system (40).…”

Investigation on the self-assembled behaviors of C18unsaturated fatty acids in arginine aqueous solution

“…The 2 H NMR technology supplies the information about the motion averaged electric quadrupole couplings between the deuterium nuclei and the electric eld gradients around the nucleus; 44 this interaction is ascribed to the motion of D 2 O molecules and is sensitive to the interface of the surfactant assemblies. 45 For a macroscopically anisotropic solution, D 2 O molecules at the anisotropic site experience a nonzero average of the quadrupole interaction, leading to a splitting of resonance, while for an isotropic environment, the interaction has a zero average due to the fast molecular motion and only a single sharp peak is obtained. Fig.…”