Cationic surfactant systems with divalent (7-9) as The isothermal ternary phase diagram for the 1-dodecylpyridinwell as monovalent counterions (9-10) have also been studium bromide (1-DPB) -water-dodecanol system was determined ied. In a large headgroup, the charge distribution (11) can at 40ЊC, using 2 H NMR, polarizing microscopy, and SAXS methalso be expected to influence both the phase stabilities and ods. All of the phases were characterized, and their ranges of structure of aggregates.
existence were determined. The surfactant is easy to dissolve in Numerous studies have been performed with alkylpyridinwater, yielding a normal micellar solution phase. After the normal ium halide surfactants, principally in terms of micellization micellar phase, on the binary surfactant-water axis, a normal and micellar structure. Among other investigations, the relahexagonal liquid crystalline phase is found at higher surfactant tion between structure and aggregation properties has been concentrations. On addition of dodecanol, four more phases are formed, i.e. a cubic, a lamellar, and a reverse hexagonal phase, investigated for a variety of branched and unbranched alfollowed by a reverse micellar solution phase. The lamellar liquid kylpyridinium halides (12), as well as the effect of the surcrystalline phase dominates the ternary phase diagram. The strucfactant alkyl chain length on its solubilization behavior (13, tures of the liquid crystalline phases were further examined using 14). The orientation of the large pyridinium headgroup of SAXS measurements, and the results are discussed in terms of the dodecylpyridinium iodide in a lyotropic liquid crystal has critical packing parameter, cpp, and electrostatic forces. The been studied by using 2 H NMR (15). The 2 H NMR spectra SAXS experiments show a pronounced swelling of the rods in the of the surfactant after deuteration of the pyridine ring provide hexagonal phase, from 28.5 to 33 A ˚on addition of dodecanol, information about the dynamic structure of this headgroup whereas the cylindrical aqueous core of the reverse hexagonal in the studied phase. phase has a diameter of 18-21 A ˚, depending on sample composi-However, only a few studies has been performed in the tion. The average bilayer thickness of the lamellar phase is about more concentrated systems. Recently, in a series of papers 24 A ˚.