Influences of alkanes on the phase behaviors of system of cationic-anionic surfactants

The effects of three straight-chain alkanes (n-pentane, n-heptane, and n-octane) on the phase behaviors of aqueous solutions of sodium lauryl sulfate and hexadecyl trimethylammonium bromide with additives of 1-hexanol and NaBr were examined. Phase diagram and polarization detection implied that the alkanes were located in the hydrophobic region of ordered aggregates while 1-hexanol and NaBr were located in the hydrophilic region, respectively, affecting the forces between surfactant molecules in the two regions. The length of alkanes was an important factor in determining the phase behaviors, especially the range and structure of liquid crystal (LC). Alkanes with shorter carbon chain are more efficient in formation of more and longer-range ordered LC structures. In addition, partial aqueous two phase (ATPS) was transformed into LC with the increase of temperature since higher temperatures provided energy for the further growth of LC.