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

We investigated the effect of surfactants on an interface between two kinds of liquids by molecular dynamics (MD) simulation. We adopted the simple bead-spring model with two atoms as the surfactants. We controlled the interfacial tension of the surfactant adsorbed on the interface by changing the bond length. Although the interface's structure 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 crossover 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.

Automated summary

We studied the effect of surfactants on the interface between two liquids using molecular dynamics simulation. Surfactants were represented by a simple bead-spring model with two atoms. By adjusting the bond length, we controlled the interfacial tension of the surfactant on the interface. The interface remained stable even at virtually zero interfacial tension, although its structure changed with different magnitudes of interfacial tension. The Fourier spectrum analysis showed a crossover from q(2) to q(4) when the interfacial tension approached zero, indicating that bending rigidity played a dominant role in the restoring force when surfactant molecules were sufficiently absorbed on the interface and the interfacial tension was close to zero, while interfacial tension dominated when it had finite values.