Water/nonane interface

As an example, we consider the response of the solvents to the charge transfer reaction A + D A + D+, which takes place at the water/octanol and water/nonane interface. Figure 11 shows the normalized non-equilibrium... 

To estimate this coefficient K, first the value of K can be determined experimentally, and the ratio D2/D1 calculated using the equation proposed by Wilke and Chang [229]. For CioEOg we obtain K = 1.8. For Tritons at the water/nonane interface the following values have been given [230] K = 1.5 for Triton X-45, and K = 0.5 for Triton X-100. For decyl dimethyl phosphine oxide (CioDMPO) the adsorption activity of which is close to that of CioEOg, a value of K = 1.3 was found by Ferrari et al. [133]. 

Figure 11. Solvent dynamical response to the charge transfer reaction A + D -> A + D+ at the water/n-nonane interface (panel a) and at the water/1-octanol interface (panel b). In panel (b), the insert shows the contribution of the water to the total signal.

Liquid-liquid interfacial tensions can in principle also be obtained by simulations, but for the time being, the technical problems are prohibitive. Benjamin studied the dynamics of the water-1,2-dichloroethane interface in connection with a study of transfer rates across the interface, but gave no interfacial tensions. In a subsequent study the interface between nonane and water was simulated by MD, with some emphasis on the dynamics. Nonane appears to orient relatively flat towards water. The same trend, but weaker, was found with respect to vapour. Water dipoles adjacent to nonane adsorb about flat, with a broad distribution the ordering is a few molecular layers deep. Fukunishi et al. studied the octane-water Interface, but with a very low number of molecules. Their approach differed somewhat from that taken in the simulations described previously they computed the potential of mean force for transferring a solute molecule to the interface. The interfacial tension was 57 11 mN m", which is in the proper range (experimental value 50.8) but of course not yet discriminative (for all hydrocarbons the interfacial tension with water is very similar). In an earlier study Linse investigated the benzene-water interface by MC Simulation S He found that the water-benzene orientation in the interface was similar to that in dilute solution of benzene in water. At the interface the water dipoles tend to assume a parallel orientation. The author did not compute a x -potential. Obviously, there is much room for further developments. 

Representative surface pressure/area per molecule isotherms from monolayers of distearoyl lecithin at the interface between 0.1M NaCl and cyclohexane, n-heptane, and isooctane at 20 °C and n-nonane and isooctane at 3°C are shown in Figure 1. Two completely independent isotherms which were actually determined some months apart for the n-heptane/O.lM NaCl interface are plotted to illustrate the precision and reproducibility of the method and the data. Quite clearly the area and surface pressure at which phase separation begins depend on the hydrocarbon component of the oil/water interfacial system. The areas and surface pressures at which phase separation occurs for these and the other solvents which have been investigated are summarized in Table I. 

The molecular structure of the interfacial region is obtainable from computer simulations (Benjamin 1996). Michael and Benjamin treated the water/hydrocarbon (Michael and Benjamin 1995) and water/nitrobenzene (Michael and Benjamin 1998) interfaces by molecular dynamics simulation. In the former system two hydrocarbons were treated n-nonane and pseudononane that consisted of globular molecules with the same mass and potential functions as the long chain actual n-nonane. The mean width 5ws of the interfacial region is related to the macroscopic interfacial tension Xws by the approximate expression ... 

Pure oil/protein solution systems The Interfacial Displacement Tensiometer was used to examine the effect of additives known to promote an appreciable interfacial rheology. The systems selected were Toluene/a-lactalbumin (100 ppm), toluene/BSA (100 ppm), and nonane/BSA (100 ppm) these systems were expected to produce highly visco-elastic interfacial films. The BSA solution when displaced by either toluene or nonane (see Figure 11) gave rise to pressure jumps on the I.D.T. traces at points equivalent to entry and exit of the narrower capillary. These peaks indicate an increased resistance to displacement of the interface associated with its deformation and changes of extent. The maximum pressures are considerably in excess of those given by the pure oil/water reference system, also shown in Figure 11. 

How sharp is the interfacial region between water and an organic liquid and what is its molecular structure Broadly, three possibilities should be considered (1) the interface is sharp and flat, as assumed in continuum models (2) the interfacial region is a mixture of the two liquids and (3) the interface is a locally sharp but rough surface that fluctuates in time. Recent computer simulations of interfaces between water and benzene, " decane, nonane, hexane, dodecane, 1,2-dichloroethane (DCE), CCU, and octanol have dealt with this issue. 

---