  We have analyzed the mechanical properties of surfactant loaded tensionless
balanced liquid/liquid interfaces using self-consistent field theory
implementing a coarse grained model. Such a tensionless state, as occurring in
microemulsions, signals a first-order interfacial phase transition.
Consequently, the interfacial area is set by the amount of surfactant in the
system. Near the bulk critical point, such systems suffer an interfacial,
so-called superflexibility (SF) critical point as soon as the tensionless state
ceases to exist. This happens when the width of the L/L interface becomes
comparable to the surfactant size. The bending rigidities vanish upon
approaching the SF-point as a power-law. Exclusively near the SF-point, the
saddle splay modulus is positive featuring the sponge phase to be its main
characteristic.
