Surface pressure and wave-damping effects of surface-active organic compounds on seawater

Abstract

The surface pressure vs concentration and area per molecule curves for monolayers of stearic acid, palmitic acid, oleic acid, palmitoleic acid, triolein, and cholesterol were determined on a clean artificial seawater surface using a modified Langmuir trough. The effectiveness of each compound at wave damping was then estimated mathematically using equations derived by Dorrestein [(1951) General linearized theory of the effect of surface films on water ripples. Proc. Amster. Aca. Sci. 54, 260–350]. We conclude from these analyses that compounds forming highly expanded monolayers on seawater are more effective at damping capillary and short gravity waves (<6 cm wavelength) and generally require lower surface concentrations for this effect than materials forming highly condensed monolayers. Maximal variations in wave amplitude attenuation by different materials are predicted for wavelengths between 2 and 6 cm. All six materials are predicted to cause some wave damping at wavelengths less than 20 cm. However, between 6 and 20 cm waves, a rapid transition occurs which makes the condensed monolayers more effective at damping the longer wavelengths.