Physical Review Letters, 2019, vol 122, 17, pp. 178003
Surfactant molecules have been extensively used as emulsifying agents to stabilize immiscible fluids. Droplet stability has been shown to be increased when ordered nanoscale phases form at the interface of the two fluids due to surfactant association. Here, we report on using mixtures of a cationic surfactant and long chained alkenes with polar head groups [e.g., cetylpyridinium chloride (CPCl) and oleic acid] to create an ordered nanoscale lamellar morphology at aqueous-oil interfaces. The self-assembled nanostructure at the liquid-liquid interface was characterized using small-angle x-ray scattering, and the mechanical properties were measured using interfacial rheology. We hypothesize that the resulting lamellar morphology at the liquid-liquid interface is driven by the change in critical packing parameter when the CPCl molecules are diluted by the presence of the long chain alkenes with polar head groups, which leads to a spherical micelle-to-lamellar phase transition. The work presented here has larger implications for using nanostructured interfacial material to separate different fluids in flowing conditions for biosystems and in 3D printing technology.