Interface aqueous solution/nitrobenzene

The interface between an aqueous solution containing a strongly hydrophilic electrolyte, e.g., LiCl, and a nitrobenzene solution containing a strongly hydrophobic salt, e.g., tetra-butylammonium tetraphenylborate (TBATPhB), schematically shown below ... 

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... 

The oscillation at a liquid liquid interface or a liquid membrane is the most popular oscillation system. Nakache and Dupeyrat [12 15] found the spontaneous oscillation of the potential difference between an aqueous solution, W, containing cetyltrimethylammo-nium chloride, CTA+CK, and nitrobenzene, NB, containing picric acid, H" Pic . They explained that the oscillation was caused by the difference between the rate of transfer of CTA controlled by the interfacial adsorption and that of Pic controlled by the diffusion, taking into consideration the dissociation of H Pic in NB. Yoshikawa and Matsubara [16] realized sustained oscillation of the potential difference and pH in a system similar to that of Nakache and Dupeyrat. They emphasized the change of the surface potential due to the formation and destruction of the monolayer of CTA" Pic at the interface. It is... 

In this chapter, the voltammetric study of local anesthetics (procaine and related compounds) [14—16], antihistamines (doxylamine and related compounds) [17,22], and uncouplers (2,4-dinitrophenol and related compounds) [18] at nitrobenzene (NB]Uwater (W) and 1,2-dichloroethane (DCE)-water (W) interfaces is discussed. Potential step voltammetry (chronoamperometry) or normal pulse voltammetry (NPV) and potential sweep voltammetry or cyclic voltammetry (CV) have been employed. Theoretical equations of the half-wave potential vs. pH diagram are derived and applied to interpret the midpoint potential or half-wave potential vs. pH plots to evaluate physicochemical properties, including the partition coefficients and dissociation constants of the drugs. Voltammetric study of the kinetics of protonation of base (procaine) in aqueous solution is also discussed. Finally, application to structure-activity relationship and mode of action study will be discussed briefly. 

Fig. 3. Schematic representation of the double layer structure at the nitrobenzene-water interface at 25 C. The full curve illustrates the potential distribution at Aq 0 = 0.2 V for the interface between a 0.1 M solution of Pn4NPh4B in nitrobenzene and a 0.05 M aqueous solution of LiCl at 25 °C. The thickness of the inner layer is assumed to be 1 nm and the potential distribution is calculated using the Gouy-Chapman theory. (Reprinted from [61]. Copyright Elsevier Seience Publishers, Amsterdam).

Fig. 9. Schematic representation of double layer structure and potential profiles of the interface between a nitrobenzene (NB) solution of 0.1 M Pn4Ph4B and an aqueous (w) solution of 0.05 M LiCl in the presence (solid line) and absence (broken line) of a saturated DLPC monolayer at the potential of zero charge, where the surface potential was assumed to be negligible. (Reprinted from [98] with permission. Copyright The Chemical Society of Japan).

Fig. 21. Logarithm of the apparent rate constant k vs the potential E relative to the reversible halfwave potential (Tafel plot) derived from ac impedance measurements of Et4N ion transfer in the absence ( ) and in the presence (V, O) of a DLPE monolayer formed at the interface between an aqueous solution of 0.1 M LiCl and a nitrobenzene solution of 0.1 M Pn4NPh4B-(-50 pM DLPE (O), and at the interface between an aqueous solution of 0.09 M LiCl+O.OI M LiOH and a nitrobenzene solution of 0.1 M Pn4NPh4B-i-20 pM DLPE (V). (After [96]).

FIG. 6 Comparison of electrocapillary curves for the interface between nitrobenzene solution of 0.1 mol dm-3 hexadecyltrimethylammonium tetraphenylborate and aqueous solution of 0.05 mol dm-3 LiF (O), LiCl (A), and LiBr ( ). (From Ref. 40, reproduced by permission. The Chemical Society of Japan.)... 

FIG. 7 Electrocapillary curves at 25°C for the interface between nitrobenzene solution of 0.1 m old m tetrapentylammonium tetraphenylborate and aqueous solution of 0.5 mol dm-3 LiCl... 

Fig. 6 Electrocapillary curves at 25 °C for the interface between nitrobenzene solution of 0.1 M tetrapentylammonium tetraphenylborate and aqueous solution of 0.05 M LiCi in the presence of x mmol dm Cl 2E4 x = 0 (curve 1), 1 (curve 2), 2 (curve 3), 5 (curve 4), 7 (curve 5), 10 (curve 6), 15 (curve 7), 20 (curve 8), 30 (curve 9), 40 (curve 10), 50 (curve 11), 70 (curve 12), 80 (curve 13), and 100 (curve 14). (From Ref [16], reproduced by permission ofThe Chemical Society of Japan.)...

Fig. 9 Schematic representation of the double-layer structure of the interface between nitrobenzene and aqueous solutions in the presence of the specific adsorption of hexadecyltrimethylammonium ions [21]. (Reproduced by permission of the Chemical Society of Japan.)...

In 1997, Harrison and coworkers reported on the synthesis of an azobenzene compound in microfluidic channels [37] for the purpose of combinatorial synthesis. The azo coupling of N,N-dimethylaniline and 4-nitrobenzene diazonium tetrafluor-oborate (Scheme 4.17) was carried out in a Pyrex microreactor driven by electro-osmotic flow. A few years later, Hisamoto et al. described a phase transfer diazo coupling reaction carried out in a microfluidic chip [38]. By providing a huge liquid-liquid interface between a solution of 5-methylresorcinol dissolved in ethyl acetate and an aqueous solution of 4-nitrobenzenediazonium tetrafluoroborate (Scheme 4.18), 100% conversion within a 2.3 s residence time was achieved. In contrast to macroscale experiments, the reaction could be accelerated and the formation of unwanted precipitates and bisazo side products was successfully suppressed. 

Oil/water interfaces are classified into the ideal-polarized interface and the nonpolarized interface. The interface between a nitrobenzene solution of tetrabutylam-monium tetraphenylborate and an aqueous solution of lithium chloride behaves as an ideal-polarized interface in a certain potential range. Electrocapillary curves of the interface were measured. The results are analyzed using the electrocapillary equation of the ideal-polarized interface and the Gouy-Chapman theory of diffuse double layers. The electric double layer structure consisting of the inner layer and the two diffuse double layers on each side of the interface is discussed. Electrocapillary curves of the nonpolarized oil/water interface are discussed for two cases of a nonpolarized nitrobenzene/water interface. 

Fig. 3. Comparison of the surface charge densities in the aqueous phase obtained by differentiation of the electrocapillary curve (o) and by integration of the differential capacity curve ( ) for the interface between O.lmoldm- TBATPB nitrobenzene solution and 0.1 mol dm LiCl aqueous solution...

We first discuss the electrocapillary phenomenon at the interface between a nitrobenzene (NB) solution of tetrabutylammonium tetraphenylborate (TBATPB) and an aqueous (W) solution of LiCl, which corresponds to the above system la. The interface was studied using the following cell at 25° C [17,18] ... 

The values of surface charge density obtained by numerical differentiation of the electrocapillary curve agreed well with those obtained by numerical integration of the differential capacity curve [17,29] (Fig. 3). These results indicate that the interface between a nitrobenzene solution of TBATPB and an aqueous solution of LiCl actually behaves as an ideal-polarized interface in a certain potential range and also that the differential capacity measurements should give essentially the same information on the electrocapillarity and the double layer structure of nitrobenzene/water interfaces as the electrocapillary curve measurements, provided that their electrocapillary maximum potential which is now equal to the potential of zero charge (pzc) and interfacial tension at the pzc (y J known. 

The general trend of reported values of Ac S pzo though differing from investigator to investigator in magnitudes, is that the potential drop across the inner layer at pzc is small, much smaller than the surface potential at mercury/solution interface. Such a small A(j)o p c value may imply the compensation of the surface potential due to water dipoles with that of oppositely oriented nitrobenzene dipoles and/or the less oriented structure of the inner layer compared with that at the mercury/aqueous solution interface. 

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