Emulsification of an oil (dodecane and diesel fuel) in salinized water was studied under turbulent and agitation-free conditions in the presence of a mixture of an ionic and a nonionic surfactant. The properties of the air−water and the oil−water interfaces were investigated using the methods of du-Nouy ring, drop resonance vibrometry, and Langmuir film balance that allowed pinpointing the relevance of certain interfacial properties in emulsification. Estimation of the droplet size and its distribution from the nanometer-tomicrometer range was carried out with optical microscopy, acoustic attenuation spectroscopy, and continuous hydrodynamic flow fractionation. These measurements provided the platform for the comparison of the emulsion droplet size with those predicted from the fluctuation of the dynamic stress in the turbulent water via a capillary hydrodynamic model. While such a comparison was reasonably meaningful for micron size emulsion droplets, production of nanometer size droplets was beyond such a rudimentary expectation. We thus carried out systematic investigations into other factors that contribute to emulsification under both agitated and agitation-free conditions. An important finding of these studies is that the infusion of air bubbles that profoundly enhance the hydrodynamic fluctuation produces mainly submicroscopic emulsion droplets, while a fluctuation inhibiting water-soluble polymer has the opposite effect. Furthermore, while a hydrophilic polymer dissolved in water enhances the ripening of the droplets with time, hydrophobic polymer in oil thwarts aging, plausibly by osmotic backpressure and interfacial stiffening, which, upon compression, acts against surface tension, thereby decreasing the chemical potential of the trapped oil molecules inside the droplet. These effects are similarly observed in spontaneous emulsifications, that is, when a layer of oil containing the additives is deposited upon the surface of the aqueous phase in the absence of any external work input.
We report two processes that enable continuous extraction of organic-free water from detergent stabilized oil-in-water emulsions. The first process is based upon a modification of the so-called "electrocoagulation", which uses electrochemically produced metal hydroxides that remove oil droplets via heterocoagulation. In this method, metal particles are deposited over a graphite anode, whereas an aluminum tube is used as a cathode in an electrolysis cell through which the emulsion flows. With an electrical potential applied between the graphite and aluminum, the metal particles are corroded to produce metal hydroxides that sweep the oil droplets from the emulsion. The study shows that the oil extraction efficiency increases with the basicity of the metal hydroxide. A second process, based on acid−base interaction as well, uses surface functionalization of nickel particles (∼45 μm) that introduces amines onto the nickel surface. Here an additional advantage is that the metal particles bound to the oil droplets can be removed from the aqueous phase with a magnetic field. While each of the above processes is effective in demulsifying water, their combination vastly improves the oil extraction efficiency. With the integrated process, the total organic content of the treated water could be as low as about 0.1 ppm with the surface tension of water (72 mN/m) being that of organic-free water.
We show that photosensitized phospholipid oxidation, initiated by the lipid-conjugated fluorophore TopFluor-PC, causes defects, namely, membrane tubes and vesicle-like structures, in supported lipid bilayers (SLBs). Lipid oxidation is detrimental to the integrity of the lipid molecules; when oxidized, they undergo a conformational expansion, which causes membrane tubes to protrude from the SLB. Lipid oxidation is verified by FT-IR spectroscopy, and area expansion is observed in Langmuir trough experiments. Upon growing to a critical length, the membrane tubes arising from SLBs rapidly undergo transition to vesicle-like structures. We find a correlation between the maximum tube length and the diameter of the resulting vesicle, suggesting the conservation of the surface area between these features. We use geometric modeling and the measured tube length and vesicle radius to calculate the tube radius; our calculated mean tube diameter of 243 nm is comparable to other groups' experimental findings. In the presence of fluid flow, membrane tubes can be extended to tens to hundreds of microns in length. SLBs composed of saturated lipids resist light-induced tubulation, and the inclusion of the lipophilic antioxidant α-tocopherol attenuates the tubulation process and increases the light intensity threshold for tubulation.
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