Monolayers of silica particles at horizontal and vertical octane−water interfaces have been studied by microscopy. It is found that their structure and stability depend strongly on the particle ...hydrophobicity. Very hydrophobic silica particles, with a contact angle of 152° measured through the water, give well-ordered monolayers at interparticle distances larger than 5 particle diameters which are stable toward aggregation and sedimentation. In contrast, monolayers of less-hydrophobic particles are disordered and unstable. Two-dimensional particle sedimentation has been observed in the case of vertical monolayers. The results have been analyzed with a simple two-particle model considering the sedimentation equilibrium as a balance between the long-range electrostatic repulsion through the oil, the gravity force, and the capillary attraction due to deformation of the fluid interface around particles. The value of the charge density at the particle−octane interface, 14.1 μC/m2, found for the most hydrophobic particles is reasonable. It drastically decreases for particles with lower hydrophobicity, which is consistent with the order−disorder transition in monolayer structure reported by us before. The pair interactions between particles at a horizontal octane−water interface have been analyzed including the capillary attraction due to undulated three-phase contact line caused by nonuniform wetting (the contact angle hysteresis). The results are in agreement with the great stability of very hydrophobic silica particle monolayers detected experimentally, even at low pH at the point of zero charge of the particle−water interface, and with the aggregated structure of hydrophilic particle monolayers.
Corrosion inhibitors have been used for many years to protect oil and gas pipelines. The application of small quantities of an inhibitor to production fluids is often one of the most cost-effective ...methods for imparting corrosion protection in a system. However, even though the practice has become ubiquitous, the industry lacks a comprehensive knowledge of what actually happens to corrosion inhibitor molecules when added into a system. The work reported in this paper addresses some of the principal properties of corrosion inhibitors and how these impact the ultimate fate of the inhibitor in a production system. Specifically, the partitioning behavior of corrosion inhibitors is discussed and how this is affected by changes in inhibitor structure, temperature, brine salinity, and oil type. Competitive, parasitic adsorption onto unwanted surfaces is discussed. The affinity of various corrosion inhibitors for sand, iron sulfide, barium sulfate, iron carbonate, and emulsion drop surfaces is presented. Additionally, the ability for corrosion inhibitors to stabilize both oil-in-water and water-in-oil emulsions is discussed. Phase inversion of the emulsion is demonstrated as production variables change. The impact of each of these factors on the in situ inhibitor availability (ISIA) and the ultimate corrosion inhibition observed in the field is presented.
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•Stable edible oil foams without added foaming agent.•Air bubbles coated by crystals of long-chain, unsaturated triglycerides.•Packing density of crystals at air bubble surfaces in ...oil depends on oil type.•Thermo-responsiveness of oil foams.•Chemical composition of high melting triglyceride crystals.
Can vegetable oils containing long-chain triglycerides be aerated to yield stable oil foams? This is based on the idea that cooling of vegetable oil results in the formation of crystals of certain triglyceride chain lengths and composition dispersed in liquid oil of other chain lengths and composition. Do such oleogels allow the formation of oil foams stabilised by adsorbed crystals?
Using two vegetable oils, the temperatures for crystal formation are determined. Crystal dispersions were characterised using rheology and optical microscopy. Oleogels were aerated using a double beater and the effects of temperature and aeration time were investigated. The stability and microstructure of the oil foams were studied visually and using microscopy. A stable oil foam was progressively destabilised on heating.
Upon cooling/warming vegetable oils, crystals of high melting triglyceride form in a low melting liquid oil - an oleogel. Such oleogels can be whipped to fabricate oil foams stabilised by fat crystals. Optimum foaming yields an over-run of ~ 40% for peanut oil and ~ 110% for olive oil. Oil foams which do not exhibit drainage, coarsening or coalescence result. We show that high melting triglyceride crystals possess a higher fraction of saturated fatty acids than the original oil. Ultra-stable oil foams can be rendered unstable by heating upon approaching the melting point of the crystals.
We have used an optical transmission microscope equipped with a digital camera and fitted with a narrow-band-pass filter to obtain absorbance images consisting of an array of pixel absorbance values. ...Absorbance images of films of carbon nanoparticles were used to derive spatially resolved images of the carbon film thicknesses with a resolution in the thickness dimension of a few nanometers. The technique was applied to the characterization of carbon nanoparticle films at cellulose-coated glass surfaces and at the oil−water interfaces of emulsion drops. For the emulsions, it was necessary to use oil and water phases of equal refractive index to avoid artifacts due to the drops acting as lenses.
Silica particle monolayers at horizontal and vertical silicone oil–water and air–water interfaces at ambient and low pH have been studied by microscopy. Very long-range repulsion between adsorbed ...particles has been detected. The two-dimensional particle sedimentation observed in the case of vertical monolayers has been analysed and reasonable values for the surface charge density at the particle–air (oil) interface have been obtained. It is found that the charge density at the particle surface in contact with air is about two times smaller than that in contact with silicone oil, in accord with the results obtained by others for a similar system but using a totally different approach.
We have investigated the effects of different concentrations of a range of surfactants on the kinetics of swelling of squalane-in-water emulsion drops by the addition of decane-in-water emulsion ...drops. Using a model described in detail in an earlier paper (Langmuir 1998, 14, 5402), we use the kinetic measurements to determine the product of the decane solubility C ∞ (expressed as a dimensionless volume fraction) and effective diffusion coefficient D for the transport of decane between drops across the aqueous continuous phase. We address the issue as to whether the decane transfer occurs by “molecular” transport or whether the surfactant micelles present in the continuous aqueous phase act as “carriers” for the decane. We have investigated swelling rates for different concentrations of two nonionic surfactants, dodecyl hexaoxyethylene glycol ether (C12E6) and dodecyl octaoxyethylene glycol ether (C12E8), the cationic surfactant tetradecyl trimethylammonium bromide (TTAB) and the anionic species sodium dodecyl sulfate (SDS). The solubilization of decane was determined for aqueous solutions of all the surfactants. For molecular transport, the product C ∞ D is predicted to be of the order of 10-17 m2 s-1 and independent of the surfactant concentration in the continuous aqueous phase. From the swelling experiments, the product C ∞ D is found to be on the order of 10-14−10-13 m2 s-1 and to increase with surfactant concentration for all species except SDS. The measured magnitudes of C ∞ D for all the surfactants are consistent with oil transfer occurring by the “micelle carrier” mechanism with negligible energy barrier to the transport process.
Drought threatens tropical rainforests over seasonal to decadal timescales, but the drivers of tree mortality following drought remain poorly understood. It has been suggested that reduced ...availability of non-structural carbohydrates (NSC) critically increases mortality risk through insufficient carbon supply to metabolism ('carbon starvation'). However, little is known about how NSC stores are affected by drought, especially over the long term, and whether they are more important than hydraulic processes in determining drought-induced mortality. Using data from the world's longest-running experimental drought study in tropical rainforest (in the Brazilian Amazon), we test whether carbon starvation or deterioration of the water-conducting pathways from soil to leaf trigger tree mortality. Biomass loss from mortality in the experimentally droughted forest increased substantially after >10 years of reduced soil moisture availability. The mortality signal was dominated by the death of large trees, which were at a much greater risk of hydraulic deterioration than smaller trees. However, we find no evidence that the droughted trees suffered carbon starvation, as their NSC concentrations were similar to those of non-droughted trees, and growth rates did not decline in either living or dying trees. Our results indicate that hydraulics, rather than carbon starvation, triggers tree death from drought in tropical rainforest.
In this paper we present a thermodynamic model for the adsorption of charged colloidal particles to air−water and oil−water interfaces from water-based suspensions and derive the equations for the ...respective particle adsorption isotherms. The effects of electrolyte concentration, surface charge density of both the particles and the air−water (oil−water) interface, particle contact angle, and particle volume fraction are studied in detail. The model is based on a detailed account of the interfacial free energy of particles and electric double layer formation, as well as collective effects related to the free energy of mixing of the particles with the liquid phases (water and oil) and surface charge displacement. The effect of particle size on the adsorption at the air−water and the oil−water interfaces is discussed. An analytical expression for the distribution coefficient of particles between oil and water has been derived and discussed in terms of the effects of electrolyte, contact angle, surface charge, and oil−water interfacial tension. The predictions of the model are in accord with relevant experimental data. The results are directly relevant for understanding the behavior of solid particles as emulsifier agents and foam stabilizers and in the process of antifoaming and liquid−liquid extraction of minerals.
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