Light Scattering Study of Capillary Waves on Water Covered by Monomolecular Films

Abstract

Light scattering techniques are used to study the dispersion relation of low amplitude capillary waves, or rippions, on water covered by various monomolecular films. Preliminary experiments on pure water rippions (without film) confirm previous work, and show that the damping of the rippions is anomalously high. We have invoked the concept of a highly structured water surface region in order to interpret our data. Further experiments on 0.01 N HC1 covered by various monomolecular films indicate that the existing theories apparently are not completely appropriate for interpreting our measurements. However, we have been able to ascertain that films with small polar head groups interact very little with the water surface, while films with large polar head groups interact so strongly that they are even able to alter the effective water surface viscosity. This is evidence for the existence of a highly structured water surface region since the films cannot affect the bulk of the 0.01 N HCI as a whole.