Dodecane-water systems interface

Fig. 13. Single molecule detection of Dil at the dodecane-water interface by fluorescence microscopy (left). Short photon burst in the SDS systems and (right) long burst in the DMPC systems.

The ability of RS molecules to form self-assembling layers at the interfaces was evaluated by means of surface tension measurements of model systems. The surface tension values determined as a function of the RS concentration at the interface of chloroform-water and dodecane-water are shown in Fig. 2. The significant decrease with increasing RS concentration suggests a surface-active character based on the molecular structure of the interfacial additive. 

Figure 7. The repeat distance, as a function of dodecane weight fraction, for a quaternary system SDS/pentanol/water/dode-cane curve 1, computed using eqs 17 and 18 curve 2, computed by assuming that the entire surfactant and cosurfactant are adsorbed on the interface. The circles represent the experimental result of Safinya et al.24...

Many examples exist of interfaces formed between two immiscible liquids. A well-known one is the interface between a long-chain hydrocarbon, for example, dodecane, and water, which is commonly known as the oil water interface. Dodecane and water are immiscible because the hydrocarbon phase is nonpolar. Liquid liquid interfaces are also formed between water and organic liquids with polar groups such as octanol and heptanoic acid, which also have rather long hydrocarbon chains. The polar liquid nitrobenzene, which has a relative permittivity of 35, is also immiscible with water. Another well-known system is the mercury polar liquid interface. This has been studied extensively, especially for aqueous electrolyte solutions. However, the mercury polar liquid interface is also an example of a metal solution interface which was considered in the previous section. The discussion here is limited to liquids with relative dielectric permittivities falling in the range 1-200, and systems which have poor conductivities as pure liquids. 

Only a few studies about aqueous films of amphiphilic random polyelectrolytes are reported in the literature. Millet et al. [239-241] have investigated by x-ray reflectivity the behavior of vertical free-standing films (Figure 29) of a series of hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) and poly(acrylic acid) (HMPAAH). The chemical structure of the polymer was presented in Sec. II.C (Eq. 2a). One of the aims of this work was to determine the microscopic structure of the films to explain the (macroscopic) stability behavior of the dodecane-in-water emulsions studied by Perrin et al. [188,189], who used the same series of amphiphilic polyelectrolytes as primary emulsifiers. The aqueous polyelectrolyte films have been used as model systems for the interstitial films separating two neighboring oil droplets of an emulsion creamed layer. The authors have assumed that the oil/water interface encountered in emulsions was suitably described by the air/water interface of the films. The HMPAANa and HMPAAH co-... 

Table 1 shows the effect of the addition of isobutanol on various properties of oil/brine/surfactant systems for TRS 10-410 and TRS 10-80. Because the same IFT values were obtained for the systems with and without IBA (Table 1), the observed differences in oil recovery cannot be explained in terms of any change in IFT. The presence of alcohol did not significantly influence the partition coefficient of surfactant in n-dodecane or n-octane. It is important to emphasize that the partition coefficient changes sharply near the ultralow IFT region (19). Thus, the partition coefficient does not appear to correlate with the oil displacement efficiency. However, the presence of isobutanol decreases the interfacial viscosity and markedly influences the flattening time of the oil droplets. It has been suggested (18) that a rigid potassium oleate film at the oil/water interface can be liquefied by the penetration of the hexanol molecules in order to produce spherical microemulsion droplets. It has been shown (14) also that for a commercial petroleum sulfonate-crude oil system, the oil droplets with the alcohol coalesce much faster than the ones without alcohol. For the systems studied here, IBA is believed to have penetrated the petroleum sulfonate film as seen by the decrease in IFV. The decrease in interfacial viscosity would presumably promote the coalescence in porous media. 

Muckerjee et al. [63-65] proposed a so-called three-phase model of the micellar solutions which considers the molecules adsorbed at the micelle surfaces as a separate phase. This model was applied to allow a comprehensive analysis of the distribution of several organic nitroxides between dodecane and water, their surface activity at this system and the solubilization constants of these nitroxides by SDS and other micelles. The high values of the binding constants of nitroxides by micelles can be explained not by their solubility in the hydrophobic nuclei of the micelles, but by their adsorption at the interface of the micelles and the aqueous phase. 

Sjoblom, J., Skurtveit, R., Saeten, J.O., and Gestblom, B. 1991. Structural changes in the microemulsion system didodeeyldimethylammonium bromide/water/dodecane as investigated by means of dieleetric spectroscopy. J. Colloid Interface Sci., 141, 329-337. 

Extensive theoretical and experimental work has previously been reported for supported liquid membrane systems (SLMS) as effective mimics of active transport of ions (Cussler et al., 1989 Kalachev et al., 1992 Thoresen and Fisher, i995 Stockton and Fisher, 1998). This was successfully demonstrated using di-(2-ethyl hexyl)-phosphoric acid as the mobile carrier dissolved in n-dodecane, supported in various inert hydrophobic microporous matrices (e.g., polypropylene), with copper and nickel ions as the transported species. The results showed that a pH differential between the aqueous feed and strip streams, separated by the SLMS, mimics the PMF required for the emulated active transport process that occurred. The model for transport in an SLMS is represented by a five-step resistance-in-series approach, as follows (1) diffusion of the ion through a hydrodynamic boundary layer (2) desolvation of the ion, where it expels the water molecules in its coordination sphere and enters the organic phase via ion exchange with the mobile carrier at the feed/membrane interface (3) diffusion of the ion-carrier complex across the SLMS to the strip/membrane interface (4) solvation of the ion as it enters... 

The effect of alcohol on the distribution of (total) water between the free and bound states was exemplified [2,9] by the swelling of a fixed amount of a 1 1 (by weight) C,2(EO)8-water mixture with increasing amounts of a 1 1 (wt/wt) solution of pentanol + dodecane. The relative amount of (total) water constantly diminished upon the addition of pentanol + dodecane, but when the alcohol concentration reached a threshold value, some of the (boimd) water became free (Fig. 11). The same phenomenon was observed in the system phosphatidylcholine (25 wt%)-tricaprylin + alcohol (60 wt% molar ratio of 1 5, respectively)-water (15 wt%). The alcohols used were ethanol, butanol, and hexanol, and the free water content increased in that order [72], The same inverse dependence on the alcohol hydrophiUcity was observed for sucrose ester-based microemulsions [29]. It seems that alcohol molecules adsorbed at the interface distort the three-dimensional network of... 

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