Effect of surfactants on the elasticity of the liquid--liquid interface

Shunta Kikuchi, Hiroshi Watanabe

Published 2022-12-09Version 1

We investigated the effect of surfactants on an interface between two kinds of liquid by molecular dynamics simulation. We found that the interfacial tension significantly depended on the bond length of the modeled surfactants. Although the structure of the interface changed depending on the magnitude of the interfacial tension, the interface was stable even under conditions where the interfacial tension was virtually zero. The Fourier spectrum of the fluctuations of the surface structure showed a crossover from $q^2$ to $q^4$ when the interfacial tension was almost zero, where $q$ is the wavenumber. This means that the bending rigidity is dominant for the restoring force when the surfactant molecules are sufficiently absorbed on the interface, and the interfacial tension is almost zero, whereas the interfacial tension is dominant when the interfacial tension is a finite value.