Krafft Temperature Depression in Quaternary Ammonium Bromide Surfactants

Substitution of a triethyl for a trimethyl headgroup in alkyltrimethylammonium or (ω-hydroxyalkyl)trimethylammonium bromide surfactants leads to a significant reduction in the Krafft temperature. This substitution allowed us to produce asymmetric bolaform surfactants that form micellar solutions at room temperature. It is reasoned that the proximity of the bromide counterion to the quaternary ammonium center stabilizes the hydrated crystal of the conventional and bolaform surfactants through Coulombic interactions. The bolaform surfactants experience further stabilization as a result of bonding between the hydroxyl functionality and the quaternary nitrogen and bromide. Substitution of ethyl for methyl groups in the headgroup increases the ion−ion and ion−dipole distances, lowering the stability of the hydrated crystal, which in turn lowers the Krafft temperature.