Heptane/water systems interface

The heptane water and toluene water interfaces were simulated by the use of the DREIDING force field on the software of Cerius2 Dynamics and Minimizer modules (MSI, San Diego) [6]. The two-phase systems were constructed from 62 heptane molecules and 500 water molecules or 100 toluene molecules and 500 water molecules in a quadratic prism cell. Each bulk phase was optimized for 500 ps at 300 K under NET ensemble in advance. The periodic boundary conditions were applied along all three directions. The calculations of the two-phase system were run under NVT ensemble. The dimensions of the cells in the final calculations were 23.5 A x 22.6 Ax 52.4 A for the heptane-water system and 24.5 A x 24.3 A x 55.2 A for the toluene-water system. The timestep was 1 fs in all cases and the simulation almost reached equilibrium after 50 ps. The density vs. distance profile showed a clear interface with a thickness of ca. 10 A in both systems. The result in the heptane-water system is shown in Fig. 3. Interfacial adsorption of an extractant can be simulated by a similar procedure after the introduction of the extractant molecule at the position from where the dynamics will be started. 

Fang, J., and Venable, R. L. (1987), Conductivity study of the microemulsions system sodium dodecyl sulfate-hexylamine-heptane-water, /. Colloid Interface Sci, 116, 269-277. 

Gu, G., Wang, W., and Yan, H. (1996), Electric percolation of water-in-oil microemulsions The application of effective medium theory to system sodium dodecylbenzenesul-fonate (DDBS)/ -pentanol/ -heptane/water,/. Colloid Interface Sci., 178(1), 358-360. 

Phosphoric acid ester was used as a model for the estimation of concentration of a reagent in an adsorbed layer by optical measurements of the intensity of a beam reflecting externally from the liquid-liquid interface. The refractive index of an adsorbed layer between water and organic solution phases was measured through an external reflection method with a polarized incident laser beam to estimate the concentration of a surfactant at the interface. Variation of the interfacial concentration with the bulk concentration estimated on phosphoric acid ester in heptane and water system from the optical method agreed with the results determined from the interfacial tension measurements... 

A somewhat different liquid/liquid system is found in the solvent extraction of copper. We have studied the system using heptane/water. These solvents are so immiscible that, as shown in Fig. 15, there is probably no extensive interphase region but a more sharply defined interface. We have shown that for the oxime ligand, Acorga P50 [4], written as HL, the mechanism of the reaction is as in Scheme 2 (Albery et al., 1984 Albery and Choudhery, 1988). 

The combination of resonance Raman microscope spectrometry and the CLM method allowed us to directly observe the Raman spectra of the liquid-liquid interface and the bulk phases by shifting the focal point of an objective lens. A schematic diagram of the measurement system is shown in Fig. 6. CLM/ Raman microscope spectrometry was applied in order to measure the rate of complex formation between Pd(II) and 5-Br-PADAP (HL) at the heptane-water interface and it was demonstrated that this method was highly useful for the kinetic measurement of the interfacial reaction [37],... 

Br-PADAP showed a significant adsorption at the interface of heptane-water under HSS conditions (5000 rpm). On the other hand, the adsorptivity at the toluene-water interface was very low. Hpan did not adsorb at the toluene-water interface at all. The adsorption constants of 5-Br-PADAP (HL) at the heptane-water and toluene-water interfaces were obtained as log K A, (cm3) = 1.64 and log KAi (cm3) =—0.367 [21]. The solvent effect on the adsorptivity of the ligand affected directly the interfacial reaction rate. In the heptane system, the Ni(II) complex was not extracted into the heptane phase. On the other hand, in toluene system, the complex was extracted very slowly. Recently, the extraction rates of Ni(II) and Zn(II) with 5-Br-PADAP were studied by means of CLM [67]. Based on the reaction mechanism shown in Scheme I, the initial formation rate was represented by... 

Doroszkowski and Lamboume (1971) also performed similar experiments on poly(methyl methacrylate) particles stabilized by poly(12-hydroxystearic acid) of low molecular weight (1600). These were spread at the -heptane/water interface. The results for this system are less amenable to comparison with theory than those described above for polystyrene stabilized latices because of the lower molecular weight of the stabilizing chains and their highly-branched character. 

Thin-film studies confirmed observations from other techniques. Among others, they revealed that the film separating two water droplets in heptane-diluted bitumen is about half the thickness when toluene is used as a solvent. Also, the film lifetime is considerably shorter in a paraffin-based system. Demulsifiers that are used in industry to lower the water content in the feed to refineries compete for the water-oil interface with a substance or substances that produce the protective steric layers. 

Unlike bromobenzene, benzyl chloride can be carbonylated in a biphasic system of heptane-water (Scheme 74) under very mild conditions. Both hydrophobic triphenyl-phosphine and amphiphilic TPPMS can serve as ligands for the process, which may mean that the reaction in this case may actually run at the interface. A strong acceleration of the reaction by anionic surfactants -C7Hi5S03Na or n-C7Hi5COONa is evidence in favor of this hypothesis.f ... 

Valinomycin dissolved in heptane interacts with aqueous solutions of potassium and sodium picrates. This does not change the interfacial tension as compared to the systems without salt [115]. On the other hand, the study of valinomycin monolayers at the water-air interface proved KCl and NaCl to similarly interact with monolayers only up to a concentration of 0.5 M. At a KCl concentration of 0.7 M the surface potential amounts to 1050 mV, while it is only 550 mV at the same concentration of... 

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