Oil-water interface

Molecular and colloidal self-assembly at the oil–water interface has numerous important applications in complex fluids, synthetic biology, food and nutrition, environmental remediation, enhanced oil recovery, and organic synthesis. The oil–water interface provides a versatile platform for engineering self-assembled structures with unique mechanical and functional properties. In particular, oil–water interfaces are commonly encountered in emulsions, which consist of nanoscale or microscale droplets of one liquid phase dispersed within a second immiscible liquid phase. From a thermodynamic standpoint, emulsions are inherently unstable and tend toward droplet coalescence and eventual phase separation. Self-assembly of amphiphilic molecules and/or particles at the interface can impart thermodynamic or kinetic stability to emulsions. To date, self-assembly at oil–water interfaces has enabled the creation of a wide range of supramolecular structures, including colloidosomes, proteinosomes, Janus structures, and nonequilibrium structured liquids. 

We have developed a novel droplet-based Langmuir film balance capable of preparing Langmuir–Blodgett (LB) films from the oil–water interface. This miniaturized Langmuir film balance is based on CDS developed in our laboratory. We have further adapted CDS to enable the study of self-assembled Langmuir monolayers at the oil–water interface, as well as the preparation of LB films directly from this interface. In conjunction with atomic force microscopy (AFM), we demonstrated the capability of CDS for investigating a natural pulmonary surfactant film self-assembled at the perfluorocarbon (PFC)–water interface. Our findings establish a new paradigm for studying self-assembled monolayers and preparing LB films at the oil–water interface. CDS therefore holds great promise for extending the applicability of the traditional LB transfer technique from the air–water surface to the oil–water interface.