Time course, capillary wave frequency

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... 

As reviewed above, there have been many QELS studies on liquid surfaces. However, until a few years ago, reports were scarce on molecular dynamics at liquid-liquid interfaces which used time courses of capillary wave frequency. Molecular collective behavior at liquid-liquid interfaces from a QELS study was first reported by Zhang et al. in 1997 [5]. 

The molecular collective behavior of surfactant molecules has been analyzed using the time courses of capillary wave frequency after injection of surfactant aqueous solution onto the liquid-liquid interface [5,8]. Typical power spectra for capillary waves excited at the water-nitrobenzene interface are shown in Fig. 3 (a) without CTAB (cetyltrimethy-lammonium bromide) molecules, and (b) 10 s after the injection of CTAB solution to the water phase [5]. The peak appearing around 10-13 kHz represents the beat frequency, i.e., the capillary wave frequency. The peak of the capillary wave frequency shifts from 12.5 to 10.0kHz on the injection of CTAB solution. This is due to the decrease in interfacial tension caused by the increased number density of surfactant molecules at the interface. Time courses of capillary wave frequency after the injection of different CTAB concentrations into the aqueous phase are reproduced in Fig. 4. An anomalous temporary decrease in capillary wave frequency is observed when the CTAB solution beyond the CMC (critical micelle concentration) was injected. The capillary wave frequency decreases rapidly on injection, and after attaining its minimum value, it increases... 

FIG. 6 Time courses of the capillary wave frequencies after injection of (a) SDS and (b) Triton X-... 

To elucidate the dynamic molecular behaviour in the phase transfer catalytic reaction, we investigated the time courses of the capillary wave frequencies after the injection of the TEAB, TPRAB and TBAB solutions into the water phase. The time just prior to... 

FIGURE 3.5. Time course of capillary wave frequency after an injection of a quaternary ammonium bromide solution (1 mM) at 283K. (a)TEAB, TPRAB and (c) TBAB. The concentration of CsHsONa in the water phase and DPPC in nitrobenzene phase was 70 mM and 1 mM, respectively. 

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