Capillary wave technique

Beside the capillary wave techniques, the oscillating bubble method belongs to the first experiments for measuring the surface dilational elasticity (Lunkenheimer Kretzschmar 1975, Wantke et al. 1980, 1993). For soluble adsorption layers it allows of the exchange of matter at a harmonically deformed bubble surface to be determined. 

Effective dilational elasticity of n-octanoic acid ( ) and dodecyl amine hydrochloride ( ) at 200 Hz, measured with a capillary wave technique according to Lucassen Hansen (1966)... 

A longitudinal wave propagation approach has been adopted in view of the problems of applying capillary wave techniques to liquid/liquid interfaces. These arise from two quarters. Firstly the variation of damping coefficient with elastic modulus can be shown (12) to be negligible at sufficiently high and low elastic moduli. 

KINETIC STUDIES ON GAS-LIQUID INTERFACE BY MEANS OF CAPILLARY WAVE TECHNIQUE... 

The scattering techniques, dynamic light scattering or photon correlation spectroscopy involve measurement of the fluctuations in light intensity due to density fluctuations in the sample, in this case from the capillary wave motion. The light scattered from thermal capillary waves contains two observables. The Doppler-shifted peak propagates at a rate such that its frequency follows Eq. IV-28 and... 

In the past five years, it has been demonstrated that the QELS method is a versatile technique which can provide much information on interfacial molecular dynamics [3 9]. In this review, we intend to show interfacial behavior of molecules elucidated by the QELS method. In Section II, we present the principle and the experimental apparatus of the QELS along with the historical background. The dynamic collective behavior of molecules at liquid-liquid interfaces was first obtained by improving the time resolution of the QELS method. In Section III, we show the molecular collective behavior of surfactant molecules derived from the analysis of the time courses of capillary wave frequencies. Since the... 

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

The electric field experiment shown here can be considered as a test case for the quantitative nature of capillary instability experiments. It shows the precision, with which the capillary wave pattern reflects the underlying destabilizing force. In the case of electric fields, this force is well understood. Therefore, the good fit in Fig. 1.10b demonstrates the use of film instability experiments as a quantitative tool to measure interfacial forces. The application of this technique to forces that are much less well understood is described in the following section. 

There are several experimental techniques suitable for studying e. Some of them are Relaxation after a sudden compression of the monolayer Electrocapillary waves An oscillatory barrier Light Scattering by thermally excited capillary waves. The first two techniques are used in the low - frequency range, below 1 Hz. The last one in the kilohertz range. 

In the Current State of the Art we will review some of the recent SANS and reflectivity data from ISIS, which also serve to point to future directions and opportunities. Recent reflectivity measurements, on the adsorption of polymers and polymer/surfactant mixtures at interfaces, surface ordering in block copolymer systems, time dependent inter-diffusion at polymer-polymer interfaces, and the contribution of capillary waves to interfacial widths, will be described. The use of SANS to investigate the dynamic of trans-esterification of polyester blends, the deformation of copolymers with novel morphologies, and the use of diffraction techniques to determine the structure of polymeric electrolytes, will be presented. 

Typically dynamic techniques (overflowing weirs, cylinders, capillary waves, etc,) will be discussed in sec. 3.7 on Interfacial rheology. 

It is beyond the present scope to discuss experimental and interpretational details. For further information a review by Miller et al. ) and the book by Dukhin et al., mentioned in sec. 1.17d, may be consulted ). In view of the interpretational problems it may be recommended to compare results obtained by different approaches. Some techniques, with a rather rheological nature (falling or overflowing films, pulsating bubbles, capillary waves, etc.) recur in chapters 3 and 4. Anticipating this, in figs. 1.30-1.32 we give some recent illustrations. 

We shall not pursue this approach here because it does not help us much in finding a molecular interpretation, certainly not for U°. Even in the absence of waves (solidified liquids), U° is substantial. Rather, this interpretation deals with a contribution to y than with y itself. However, we recall that the capillary wave connection had already occurred in the technique for measuring surface tensions from surface light scattering, see Mandelstam s equation [1.10.1], from which an explicit formula for y may be derived. 

Finally, we recall that surface light scattering is another modem technique. Essentially. thermal capillary waves can be studied and this enables us to derive interfacial tensions and binding constants. We discussed this matter in sec. 1.10. 

Depth profiling techniques applied to thermodynamically equilibrated thin films characterize the compositions of coexisting phases and the spatial extent of the separating interface. This procedure repeated at different temperatures yields the coexistence curve and the corresponding temperature variation of the interfacial width. Determined coexistence curves are well described by the mean field theory with composition-dependent bulk interaction parameter [74]. The same interaction parameter also seems to generate the interfacial widths in accordance with results presented here [107] (Sect. 2.2.2) and elsewhere [88, 96, 129]. These predictions may however need to be aided by capillary wave contributions to fit another observations [95, 97, 98], especially those tracing the change of the interfacial width with film thickness [121,130] (see Sect. 3.2.2). 

Applications of this nonlinear laser imaging technique holds the promise of directly studying the effect that capillary wave stresses exert upon the surfactant layer as well as those exerted by the surfactant on the water surface. The importance of capillary wave/surfactant dynamics at the ocean underscores the importance of these experiments and suggests that further efforts directed toward extending these experimental techniques to in situ ocean studies would be most useful. 

How do the predictions of capillary wave persistence to the molecular scale correlate with experiment Scattering techniques are detailed probes of interfacial structure The quasi-elastic scattering of light, the reflection of X-rays, and the reflection of neutrons have all been used as experimental probes of liquid interfacial structure. Schlossman and co-workers [27] have employed... 

---