Location of Solubilized Oil in Lyotropic
Surfactant
Liquid Crystalline Phases and
the Resulting Effects on Phase Equilibria
Peter K. Kilpatrick, John C. Blackburn, and Theodore
A. Walter
Department of Chemical
Engineering,
Received
The location of solubilized oil in
surfactant liquid crystalline aggregates can have a pronounced effect on phase
stability and their compositional extent. Detailed experimental ternary phase
diagrams of sodium 1-tetradecanoate, water, and four different hydrocarbons, n-decane, n-hexadecane, toluene, and 1-decanol, are
presented. The phase diagrams were constructed through two primary methods: optical
birefringence and quadrupole NMR spectroscopy. The
results reveal a strong dependence of liquid crystalline phase stability on oil
type, through the location of solubilized oil in the
surfactant aggregate. n-Decane
and n-hexadecane are shown to be primarily solubilized
in the interior or core of the aggregates, toluene is solubilized
in both the core and palisade or interfacial layer, and 1-decanol is primarily solubilized in the palisade layer. A simple geometric model
of core and palisade solubilization is able to rationalize
the shape of the ternary liquid crystalline single phase regions comprised of
cylindrical hexagonal phase aggregates. Quadrupole
NMR spectroscopy of deuterated toluene confirms its solubilization in both core and palisade regions in
lamellar phases.