Effect of an external field on capillary waves in a dipolar fluid

A well-known aspect of liquid/vapor systems is the presence of capillary waves at an interface. Capillary waves are density fluctuations that result of a balance between thermal fluctuations and the surface tension. The role of an external field on capillary waves at the liquid-vapor interface a dipolar fluid is investigated using molecular dynamics simulations. For fields parallel to the interface, the interfacial width squared increases linearly with respect to the logarithm of the size of the interface across all field strengths tested. The value of the slope decreases with increasing field strength indicating that the field dampens the capillary waves. With the inclusion of the parallel field, the surface stiffness increases with increasing field strength faster than the surface tension. For fields perpendicular to the interface, the interfacial width squared is linear with respect to the logarithm of the size of the interface for small field strengths and the surface stiffness is less than the surface tension. Above a critical field strength that decreases as the size of the interface increases, the interface becomes unstable due to the increased amplitude of the capillary waves.