Phase behavior
Hydrotropes increase the solubility of organic molecules in
water by mediating the interactions between hydrophilic and
hydrophobic molecules. When they are combined with surfactants
or amphiphilic copolymers in a medium, the resulting phase
behavior is dominated by a balance of solvation forces. In
microemulsion hydrotropes often act as “coupling agents”
increasing the extent on a phase diagram of the aqueous or reverse
micelle phases and, at higher concentrations, bridging the two
phases and creating a continuous passage fromthe water-rich to oilrich
side of the appropriate ternary diagram. This phenomena was
studied by Friberg and coworkers [19,20] for microemulsions
formed with ionic surfactants. They concluded that it is the
disruption of the lamellar liquid crystalline phase by the
hydrotropic molecules that drives the growth and merger of the
two micellar phases. Similar effects on the phase behavior of
solutions of cetyl trimethylammonium bromide (CTAB)/pentanol/
water induced by the addition of the pharmaceutical hydrotropes
penicillin-k [21] and cephanone [22] have also been reported