Capillary waves power spectra

First, a typical power spectrum of capillary waves excited at the W/NB interface is shown in Figure 3.4a. The errors on the values of the capillary wave frequency were 0.1 kHz, obtained as the standard deviation of 10 repeated measurements. Capillary wave frequency dependence on CeHsONa is shown in Figure 3.4b. The frequency decreased significantly with increasing CeHsONa concentration. This indicated that interfacial tension was decreased by the interfacial adsorption of CeHsONa. 

FIGURE 3.4. (a) Power spectrum for capillary waves excited at the W/NB interface (238 K). (b) Capillary wave frequency dependence on the concentrations of CsHsONa (283 K). 

Fig. 5. Typical power spectrum of the optically mixed light intensity. O/W, ripplon (capillary wave) frequency at nitrobenzene-water interface W/A, ripplon frequency at water-air interface. (Reprinted from [76] with permission. Copyright The Japan Society of Analytical Chemistry).

More recently, Samec and coworkers investigated the line shape of the fluctuation spectrum at the polarizable water/DCE interface in the presence of the phospholipid DL-a-dipahnitoyl-phosphatidylcholine (DPPC) [32]. The line shape of experimental power spectra similar to those exemplified in Pig. 4.12 b was analyzed in terms of the mean vertical displacement of the interface generated by capillary waves. The experimental results in the presence and absence of DPPC at a wide potential range appear consistent with the description of the liquid/liquid boundary as molecularly sharjf. However it is not entirely clear from this analysis how sensitive the spectmm line shape is to the molecular organization at the liquid/Hquid boundary. As discussed in Section 4.3.2, vibrational sum frequency generation studies of the neat water/DCE interface provide a rather different conclusion. 

The spectrum of light scattered by the capillary waves is just the power... 

Figure 3.16. The power spectrum of capillary waves on a liquid surface with the following properties yo = 50 mNm , y = 2 X 10 mNsm", o = 10 mNm , a = 0 mN s m . The inset is the heterodyne correlation function of this power spectrum.

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