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.
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