Jean Lachaise

Strong Specific Hydroxide Ion Binding at the Pristine Oil/Water and Air/Water Interfaces

Despite claims, based largely on molecular dynamics simulations, that the surface of water at the air/water interface is acidic, with a positive charge, there is compelling experimental evidence that it is in fact basic, with a negative charge due to the specific adsorption of hydroxide ions. The oil/water interface behaves similarly. The pH dependence of the zeta potentials of oil drops has been measured by two very different techniques: on a single drop in a rotating electrophoresis cell and on about 10(14) submicrometer drops in a 2 vol % emulsion by an electroacoustic method to give similar results with a sigmoidal pH dependence characterized by an isoelectric point at pH 2-3 and a half adsorption point about pH 5.5, or at 10(-8.5) M hydroxide ion. This indicates that hydroxide ion is absorbed much more strongly than other anions. The pH dependence of a single N(2) bubble has also been measured and has the same pH dependence, independently of whether HCl or HI is used to adjust the pH. These similarities between the pH dependences of the zeta potentials of air bubbles and oil drops, as well as those reported from streaming potentials on solid inert surfaces such as Teflon, indicate that water behaves similarly, with only subtle differences, at each of these low dielectric hydrophobic surfaces, with an isoelectric point of pH 2-4. In acidic solutions at pHs below the isoelectric point, the surface is indeed positive, consistent with spectroscopic observations of the adsorption of hydrogen ions.

Solubilization of polar oils with extended surfactants

Starting with previous results showing that the solubilization of oil and water in a microemulsion can be improved by the introduction of an additive, i.e. a so-called lipophilic linker, a new surfactant type that mimics the additive effect is tested. The so-called extended surfactant has a poly-propylene oxide chain inserted in between the conventional alkyl and ether sulfate groups. These surfactants exhibit a critical micelle concentration and a cloud point that changes with the number of propylene oxide groups per molecule (ranging from 6 to 14). They show three-phase behavior at optimum formulation, with hexadecane, ethyl oleate, and, as reported for the first time, with triglyceride oils, such as soya oil. Outstanding values of the optimum solubilization parameter are reached (in the 10–30 ml g−1 range).

Modelling of the surface tension of pure components with the gradient theory of fluid interfaces: a simple and accurate expression for the influence parameters

In this work the gradient theory of fluid interfaces is used to compute the surface tension of substances of industrial interest (hydrocarbons, gases and refrigerants) once an expression has been derived for their influence parameters. The vapour-liquid equilibria are first determined with a volume-corrected Peng-Robinson equation of state (PR-EOS). The volume corrections are accurately described by a correlation similar to the one suggested by Soreide, but with new parameters regressed on experimental data of the fluids considered here. The influence parameters are computed for each fluid outside the critical region. The results support the assumption that the density-dependence of the influence parameter can be neglected while a temperature-dependence needs to be conserved. A simple correlation is derived to account for this temperature-dependence. For hydrocarbons and gases, the parameters of the temperature-dependence are correlated with the acentric factor; for refrigerants, they are kept constant. When the gradient theory is applied with the expression presented here for the influence parameter and combined with the volume-corrected PR-EOS, the overall average absolute deviations of the calculated surface tensions is 2.2% for hydrocarbons and gases, 4% for refrigerants.

An extended scaled equation for the temperature dependence of the surface tension of pure compounds inferred from an analysis of experimental data

Abstract We have made a literature survey and performed a critical analysis of the available experimental surface tension data for the most volatile compounds in petroleum fluids: nitrogen, methane, ethane, propane, i-butane, n-butane, n-pentane, n-hexane, n-heptane and n-octane. Including the selected data with those for oxygen, xenon, krypton and those obtained recently for 16 partially halogenated hydrocarbons (refrigerants), we propose the following extended scaled equation to represent the surface tension of these substances: σ=kT c N A V c 2/3 (4.35+4.14ω)t 1.26 (1+0.19t 0.5 −0.25t) where t1−T/Tc is reduced temperature, k, NA, Vc, and ω are the Boltzmann constant, Avogadro number, the critical volume and the acentric factor, respectively. This equation, which only differs slightly from that proposed by Schmidt et al. [J.W. Schmidt, E. Carrillo-Nava, M.R. Moldover, Fluid Phase Equilibria 122 (1996) 187–206] for refrigerants, yields values for σ within 3.5% of the experimental values for all these compounds. Available data for other compounds (refrigerants) are in agreement with this relation; in the light of that we also examine some compounds (carbon dioxide and argon) for which there exist conflicting datasets.

Partitioning of ethoxylated alkylphenol surfactants in microemulsion-oil-water systems☆

Ethoxylated alkyl phenol oligomer partitioning between the microemulsion-water-oil (heptane) phases of a Winsor III system is determined by high performance liquid chromatography for systems containing octyl, nonyl, decyl, dodecyl and dinonyl phenol species. The partition coefficient between the water and oil phases obeys a simple law depending upon the alkyl chain length and the number of ethylene oxide groups per oligomer molecule. The results allow estimation of the energy of transfer of an ethylene oxide group and of a methylene group from oil to water.

SURFACTANT-OIL-WATER SYSTEMS NEAR THE AFFINITY INVERSION PART VIII : OPTIMUM FORMULATION AND PHASE BEHAVIOR OF MIXED ANIONIC-NONIONIC SYSTEMS VERSUS TEMPERATURE.

ABSTRACT Surfactant-oil-water systems with a phase behavior insensitive to temperature and composition can be achieved by anionic-nonionic mixing. By using of a linear mixing rule and a linear temperature dependency, it is possible to interpret most of the features exhibited by the experimental phase behavior data obtained with sulfonate and ethoxylated alkylphenol mixtures. Deviation from the theoretical model are probably due to anionic and nonionic groups association which reduces the overall hydrophilic character.

Interactions and coalescence of nanodroplets in translucent O/W emulsions

Abstract A thermal protocol has allowed us to produce translucent O/W emulsions composed of nanodroplets. By means of a static light scattering analysis, we show that the interaction potential existing between nanodroplets is practically a hard sphere interaction potential. Dynamic light scattering measurements bring us to study the steric effect induced by the surfactant molecules which are adsorbed at the water/oil interface. We confirm that nanodroplet dynamic coalescence rates are slowed down when the surfactant molecular weight is high.

Partitioning of Nonionic and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases

Mixtures of different surfactant types have been proposed for application in polymer/micellar flooding processes. In some cases, severe fractionation of such mixtures is found even in short core experiments. In this paper, a new theory of surfactant partitioning between phases is developed and tested. Polydisperse nonionic surfactants blended with an anionic surfactant are considered. Important parameters in the theory are the critical micelle concentrations (CMCs) of surfactant mixtures in water and the partition coefficients of the surfactant between oil and water measured at total surfactant concentrations less than the CMC. From these simple experiments, surfactant fractionation in microemulsion systems can be modeled. The authors show that the fractionation of polydisperse ethoxylated nonionic surfactants between excess oil and water phases is not as severe in the presence of anionic surfactants as it is in systems containing only nonionic surfactants.

New formulation of blood substitutes: optimization of novel fluorinated microemulsions

The synthesis of a novel microemulsion system composed of a mixed fluorinated and hydrogenated oil C8F17CH2CHCHC4H9 with a biocompatible hydrogenated surfactant, Montanox 80 is described. Investigation of the solubility of oxygen in these microemulsions showed that they absorbed more oxygen than Fluosol-DA which is currently used as an oxygen transporter in biomedical applications. Oxygen absorption was similar to that of blood. Light scattering studies showed that the system was composed of small sized aggregates which should in principle be compatible with blood. The toxicity of the microemulsions was tested after intraperitoneal injection in rats, and in mice after intravenous administration. The microemulsions appeared to be well tolerated. These results show promise for the development of oxygen transporting compounds.

PARTITIONING OF ETHOXYLATED ALKYLPHENOL SURFACTANTS IN MICROEMULSION-OIL-WATER SYSTEMS. PART II : INFLUENCE OF HYDROPHOBE BRANCHING

Abstract Ethoxylated alkylphenol surfactants fractionation between oil and water is best studied in three-phase so-called optimum formulation systems, in which a microemulsion is in equilibrium with both oil and water excess phases. The partitioning is found to be slightly affected by the structure of the surfactant hydrophobe. It is found that the more the branching the more the surfactant tends to partition into the water phase, and less into the oil phase. The study includes data for linear and branched alkylate species as well as multiple alkyl group species.