Naslov
Structure of Liquid Crystalline Aerosol-OT and its Alkylammonium Salts

Autori
Ungar, Goran ; Tomašić, Vlasta ; Xie, Fangning ; Zeng, Xiang-bing

Izvornik
Langmuir (0743-7463) 25 (2009), 18; 11067-11072

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
catanionic surfactants

Sažetak
Aerosol-OT is a widely used anionic surfactant, and its lyotropic properties have been studied extensively. However, neat AOT is itself liquid crystalline. We carried out an X-ray study of neat AOT sodium salt, as well as of AOT -n-decyl-, n-dodecyl-, n-tetradecyl-, and n-hexadecylammonium salts. We confirm an earlier report that pure AOT forms a hexagonal columnar phase, but propose a different packing model. This involves a relatively highly ordered structure with each column cross-section containing three tessellated molecules in the plane normal to the column axis. The structure is trigonal locally, but hexagonal over the long range. This mode of assembly is supported by electron density reconstruction and molecular modelling. At subambient temperatures the AOT – alkylammonium complexes Cn-AOT, with n = 10-16, also display a hexagonal columnar phase, but this is more disordered and each column cross-section contains only two ion pairs. Unusually, molar enthalpy and entropy of the columnar-isotropic transition in Cn-AOT salts decrease with increasing n. This is attributed to a disproportionally high conformational disorder of the radial chains in the columnar phase, which is required for efficient space filling.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA