Chemistry Reference
In-Depth Information
Laboratory study of the damping of parametric ripples
due to surfactant films
Stanislav A. Ermakov and Sergei V. Kijashko
Institute of Applied Physics, Nizhny Novgorod, Russia
Abstract.
Laboratory studies of damping of capillary-gravity waves
(CGW) due to organic films were carried out in a wide range of surfactant
concentrations using a method of parametrically excited surface waves
(Faraday ripples) at wave frequencies from about 15 Hz to 30 Hz. The
threshold acceleration for CGW excitation and CGW wavelengths were
measured and the wave damping and the surface tension coefficients were
retrieved for a clean water surface and for water covered with organic
films. It is obtained that the damping coefficient for ordinary surface-
active substances (e.g., oleyl alcohol and oleic acid) exhibits a maximum
at small surfactant concentrations, comparable with the concentrations
needed for monomolecular coverage and remains practically constant at
large concentrations. The damping coefficient for polymer films (poly-
oxyalkylene glycol - “Emkarox”) shows two maxima, one of which is a
narrow peak at small concentrations similar to the case of ordinary surfac-
tants, and a "plateau"-like maximum at large concentrations. The dynamic
film elasticities are retrieved from the measured damping coefficient using
a theory of wave damping for purely elastic films. The dynamic elasticities
are shown to differ strongly from the static elasticities, especially at large
surfactant concentrations.
1 Introduction.
Damping of gravity-capillary waves due to organic films has been a prob-
lem of long-term interest in physico-chemical hydrodynamics (Levich
1962, Lucassen-Reynders and Lucassen 1968), the problem also is very
important in oceanography, in particular, in studies of organic slicks on the
ocean surface and their remote sensing using radar and optical methods
(Alpers and Hühnerfuss 1989, Scott 1986, Scott and Thomas 1999 and the
references therein). The most interesting aspect for remote sensing of
slicks with C-, X-, K
u
-, and K
a
-band radars is the damping of centimetre-
