High-resolution NMR characterization of a gel-like surfactant mesophase.
The addition of phosphatidylcholine to AOT water-in-oil microemulsions leads to the formation of a rigid gel as the water content is increased above a specific threshold. This system is a gel-like crystalline phase where the microstructure evolves from reverse hexagonal to lamellar with increasing water content and/or temperature. Couette sheared (1)H and (31)P NMR experiments carried out at varying temperature and water content show distinct signatures with microstructure evolution. Because the system has been fully characterized through small-angle neutron scattering, it is possible to relate the NMR signatures to the microstructure. The NMR technique therefore complements scattering techniques but is additionally useful because the technique also picks up isotropic signatures from concurrently occurring noncrystalline phases. The use of NMR to identify such lyotropic gel-like crystalline phases allows easy correlation between templated materials synthesis in these phases and phase microstructure. NMR can therefore be used as a probe to understand microstructure in specific surfactant systems and to characterize the retention of microstructure during materials synthesis.
Liu
Limin
L
Department of Chemical and Biomolecular Engineering, Department of Chemistry, and Coordinated Instrumentation Facility, Tulane University, New Orleans, Louisiana 70118, USA.
Tan
Grace
G
McPherson
Gary
G
John
Vijay T
VT
Maskos
Karol
K
Bose
Arijit
A
D016880:Anisotropy; D003460:Crystallization; D005782:Gels; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008422:Materials Testing; D009821:Oils; D010713:Phosphatidylcholines / Q000737:chemistry; D010759:Phosphorus Isotopes / Q000737:chemistry; D012542:Scattering, Radiation; D013314:Stress, Mechanical; D013499:Surface Properties; D013501:Surface-Active Agents; D013696:Temperature; D014867:Water / Q000737:chemistry
D005782:Gels; D009821:Oils; D010713:Phosphatidylcholines; D010759:Phosphorus Isotopes; D013501:Surface-Active Agents; D014867:Water