Microemulsion sponge phase as a manifestation of the superflexibility critical point of tensionless balanced liquid-liquid interfaces

TL;DR

This paper investigates the superflexibility critical point in tensionless balanced liquid-liquid interfaces, revealing how surfactant properties influence phase transitions and the emergence of sponge phases.

Contribution

It introduces a theoretical analysis of the superflexibility critical point in tensionless interfaces using self-consistent field theory, highlighting the role of surfactant size and interface width.

Findings

Bending rigidities vanish near the SF-point following a power-law.

The sponge phase is characterized by a positive saddle splay modulus.

Tensionless states are linked to first-order interfacial phase transitions.

Abstract

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.