Shear-Induced Orientation of a Rigid Surfactant Mesophase

Abstract

An optically clear, crystalline, gel-like mesophase is formed by the addition of water to a micellar solution consisting of a mixture of 0.85 M anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and a 0.42 M zwitterionic surfactant phosphatidylcholine (lecithin) in isooctane. At 25 °C and water to AOT molar ratio of 70, the system has a columnar hexagonal microstructure with randomly oriented domains. The shear-induced orientation and subsequent relaxation of this structure were investigated by rheological characterization and small-angle neutron scattering (SANS). The rheological response implies that the domains align under shear, and remain aligned for several hours after cessation of shear. Shear-SANS confirms this picture. The sheared gel mesophase retains its alignment as the temperature is increased to 57 °C, indicating the potential to conduct templated polymer and polymer−ceramic composite materials synthesis in aligned systems.

Characterization of Ceramics by X‐Ray and Neutron Small‐Angle Scattering

“…The ability of SAS methods to quantify structures over an extended scale regime from nanometers to micrometers has made them particularly suitable as a diagnostic tool in new materials development for nanotechnology 30,31,51,52,76,82–85,90,143–166 . Whereas electron microscopy provides detailed local information for a nanostructured or nanoparticulate morphology, SAXS and SANS provides complementary, quantitative, microstructure information that is statistically representative over macroscopic sampling volumes.…”

Cryo-Field Emission Scanning Electron Microscopy Imaging of a Rigid Surfactant Mesophase

“…Of particular interest are rigid gel-like crystalline mesophases that can be aligned through shear or extrusion and can be used to template materials in both the aqueous and/or nonaqueous domains 18-20. We have extensively studied such a system that consists of bis(2-ethylhexyl) sodium sulfosuccinate, the zwitterionic surfactant l -α-phosphatidylcholine (lecithin), isooctane, and water.…”

“…We have extensively studied such a system that consists of bis(2-ethylhexyl) sodium sulfosuccinate, the zwitterionic surfactant l -α-phosphatidylcholine (lecithin), isooctane, and water. The system has similar proportions of water and oil and forms gel-like rigid mesophases with low shear viscosities of up to 10 5 Pa s. The system is optically clear with no phase separation indicating nanostructured water and oil regions 18,21-23. The microstructure of these mesophases has been previously characterized using small-angle neutron scattering (SANS)18,22,23 and nuclear magnetic resonance (NMR) spectroscopy 24,25.…”

Nanocharacterization of Lyotropic Liquid Crystalline Systems

“…Combining SANS with rheological measurements has also allowed nanostructural alignment of LLCs in shear fi elds to be demonstrated. (Singh et al, 2004 ).…”