Dodecane-water Interface Research Articles

Using the pH sensitivity of switchable surfactants to understand the role of the alkyl tail conformation and hydrogen bonding at a molecular level in elucidating emulsion stability

HypothesisThe monoalkyl diamine surfactant, N-dodecylpropane-1,3-diamine (DPDA), is expected to exhibit a pH-dependent charge switchability. In response to pH changes, the interfacial self-assembly of DPDA becomes an intermediary constituent that can potentially modify the interfacial interactions and structural assembly of both the oil and water phases. Hence, we hypothesize that as we change the pH, DPDA will respond to it by changing its charge and alkyl tail conformation as well as the conformation of adjacent phases at the molecular level, consequently affecting emulsion formation and stability. A neutral pH, resulting in a mono-cationic dialkyl amine, affects the conformation, driving an ordered self-assembly and stable emulsion. ExperimentsThe pH-sensitivity and interfacial activity of DPDA were evaluated through pH titration and interfacial tension measurements. Subsequently, a molecular-level study of DPDA, as a pH-sensitive switchable surfactant, was performed at the dodecane-water interface using SFG spectroscopy. The interpretation of the vibrational spectra was further reinforced by determining the gauche defects in the interfacial alkyl chain organization and the extent of hydrogen (H) bonding between the interfacial water molecules. FindingsBy adjusting the pH of water, the charge of the adsorbed DPDA molecules, their self-assembly, the organization of interfacial molecules, and ultimately the stability of the emulsion were tuned. At pH 7.0, the SFG spectra of DPDA showed that the interfacial alkyl chains were relatively well-ordered, while water molecules also had stronger H-bonding interactions. As a result, the oil–water emulsion showed improved stability. When water was at a high pH, the water molecules had fewer H-bonding interactions and relatively disordered alkyl chains at the interface, providing desirable conditions for demulsification. These observations were compatible with the observation in bulk emulsion preparation, confirming that alkyl chain packing and water H-bonding interactions at the interface contribute to overall emulsion stability.

Factors Influencing Pseudomonas aeruginosa Initial Adhesion and Evolution at the Dodecane-Water Interface.

Bacterial adhesion and evolution at the oil-water interface are important for a broad range of applications such as food manufacturing and microbial-enhanced oil recovery, etc. However, our understanding on bacterial interfacial adhesion and evolution, particularly at the single-cell level, is still far from complete. In this work, by employing Pseudomonas aeruginosa PAO1 at the dodecane-water interface as a model system, we have studied the effects of different factors on bacterial interfacial adhesion and the dynamic evolution of bacterial interfacial behavior at the single-cell level. The results show that PAO1 cells displayed a chemotactic behavior toward dodecane. Among the tested factors, bacterial initial interfacial attachment showed a negative correlation with the secreted cell-surface associated lipopolysaccharide and Psl while a positive correlation with type IV pili. Adding nonbiological surfactant Pluronic F-127, as expected, greatly reduced the cell interfacial adhesion. More importantly, the dynamics analysis of cell attachment/detachment at the dodecane-water interface over a long-time scale revealed a reversible to irreversible attachment transition of cells. This transition is accompanied with the interface aging resulting from bacterial activities, which led to an increase of the interfacial viscoelasticity with time and finally the formation of the gel-like interface. Further analysis demonstrated the important role of exopolysaccharides in the latter process. Our findings provide more details of bacterial oil-water interfacial behavior at the single-cell level and may shed light on developing new strategies for controlling bacterial colonization at the oil-water interface.

Effect of double chain anionic surfactant on the dynamic interfacial tensions of betaine solutions

To clarify the effect of the anionic surfactant with double alkyl chains on the interfacial tension (IFT) of betaine solutions, the IFT values of the sodium dialkyl sulfosuccinates (AOT) mixed with different betaines (alkyl sulphobetaine (ASB) and benzyl substituted alkyl sulphobetaine (BSB)) against n-alkanes and crude oil were detected by the spinning drop method. Additionally, molecular dynamics (MD) simulation was employed to verify the interaction mechanism between AOT and different betaine molecules. The results demonstrate that AOT molecules reach hydrophilic-lipophilic balance and form a relatively compacted interfacial film at the dodecane-water interface. Owing to the flexible double alkyl chains, AOT molecules possess a robust self-regulating ability at the oil–water interface. It is the self-regulating ability of AOT molecules and the electrostatic attraction between betaines and AOT molecules that achieve superior synergistic effects between AOT and betaine molecules with different molecular sizes. Besides, mixed adsorption and hydrophilic-lipophilic balance (HLB) reduce the IFT values of mixed systems containing AOT and different betaines effectively. The equilibrium IFT of the AOT-ASB system and the AOT-BSB system can be reduced to ultralow vales of 5.7 × 10−3 mN/m and 8.2 × 10−3 mN/m, respectively. At the crude oil–water interface, active components in crude oil compete with AOT molecules, which results in a significant increase in IFT values for AOT solution alone. Despite the different molecular sizes of ASB and BSB molecules, the flexible double alkyl chains of AOT molecules enable AOT to have synergistic effects with both ASB and BSB molecules at crude oil–water interface. Ultralow IFTs against crude oil can be obtained at optimized ratio of AOT to betaines, which is meaningful for the application of mixed solutions containing betaines and anionic surfactants in enhanced oil recovery.

Mechanical properties of thin films at the dodecane-water interface, for multilayered emulsion applications

The use of polyelectrolyte multilayers (PEMs) as emulsifying layers at an oil-water interface has significant potential to enhance emulsion application and function. In spite of this potential, there are few studies that directly probe the mechanical properties of interfacial layers of PEMs at the oil-water interface, properties that will influence significantly their range of applicability in emulsion science. We report here a study where we have explored the formation and mechanical properties of polystyrene sulfonate (PSS) and polydiallyldimethylammonium chloride (PDADMAC) multilayers at an oil-water interface. The study of mechanical properties as a function of layer number has revealed differences for the interface depending on the identity of the multilayer terminating layer. Specifically, PDADMAC-terminated films were much more resistant to deformation and remained elastic over a much larger percentage deformation than the films terminated with PSS. The effect is seen to persist with each bilayer, with the interface cycling between elastic/deformable up to the measured maximum number of bilayers. Within this outer layer effect data, the range of the determined mechanical properties were: surface shear moduli ranging between 35 and 60 mN ∙ m − 1 ; bulk shear moduli ranging from 0 to 10 MPa. The data indicate that there is promise in the use of PEM emulsifying layers, allowing for tailoring of the physical stability of emulsion droplets, and thus aiding in prolonging product stability and shelf life.

Surface Freezing of Cetyltrimethylammonium Chloride-Hexadecanol Mixed Adsorbed Film at Dodecane-Water Interface.

The surface freezing transition of a mixed adsorbed film containing cetyltrimethylammonium chloride (CTAC) and n-hexadecanol (C16OH) was utilized at the dodecane-water interface to control the stability of oil-in-water (O/W) emulsions. The corresponding surface frozen and surface liquid mixed adsorbed films were characterized using interfacial tensiometry and X-ray reflectometry. The emulsion samples prepared in the temperature range of the surface frozen and surface liquid phases showed a clear difference in their stability: the emulsion volume decreased continuously right after the emulsification in the surface liquid region, while it remained constant or decreased at a much slower rate in the surface frozen region. Compared to the previously examined CTAC-tetradecane mixed adsorbed film, the surface freezing temperature increased from 9.5 to 25.0 °C due to the better chain matching between CTAC and C16OH and higher surface activity of C16OH. This then renders such systems much more attractive for practical applications.

Aqueous Film-Forming Foams Exhibit Greater Interfacial Activity than PFOA, PFOS, or FOSA.

Perfluoroalkyl acids spontaneously concentrate at air-water and non-aqueous phase liquid (NAPL)-water interfaces, which can influence their retention during subsurface transport. This work presents measurements of air- and NAPL-water interfacial tension for synthetic groundwater containing perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorooctanesulfonamide (FOSA), or aqueous film-forming foam (AFFF) formulations at concentrations ranging from 0.1 to greater than 1000 mg/L. The NAPLs tested included dodecane, tetrachloroethylene, and jet fuel. AFFF formulations were less efficient at lowering interfacial tension than PFOA, FPOS, or FOSA substances below 100 mg/L, while above 100 mg/L, these formulations were more effective, achieving tensions of less than 3 mN/m. Infiltration of solutions with such low tension could lead to mobilization of residual NAPL. Equations based on interfacial tension measurements show that concentrations of PFOA, PFOS, and FOSA at the air-water interface were from 2 to 16 times greater than at the NAPL-water interface below 100 mg/L and were 10-50 times greater for AFFF below 20 mg/L. Calculations for unsaturated soil estimate that up to 87% of PFOS mass was at the air-water interface and less than 4% at the dodecane-water interface for bulk-water concentrations below 1 mg/L.

High Internal Phase Emulsions Stabilized by a Zeolite-Surfactant Combination in a Composition-Dependent Manner.

As a step toward synthesizing zeolite-based porous materials, this study demonstrates for the first time the feasibility of stabilizing oil-in-water (O/W) high internal phase emulsions (HIPEs) using a cationic surfactant (tetradecyltrimethylammonium bromide, TTAB) and "homemade" submicronic Linde type A zeolite particles. The zeolite particles are hydrophilic and therefore do not attach to dodecane-water interfaces, but surface tension measurements and electrochemical data show that their surface can be activated by the electrostatic and subsequent hydrophobic adsorption of TTAB. Comparing the adsorption isotherm of TTAB and zeta potential of the particles with the droplet sizes and rheological properties of the emulsion shows that the stabilization mechanism depends on the TTAB/zeolite weight ratio. At low TTAB/zeolite weight ratios (≤0.2 wt %), gel-like O/W Pickering HIPEs form, but at intermediate TTAB concentrations, the zeolite particles become more hydrophobic, leading to phase inversion and the stabilization of W/O emulsions. At high TTAB/zeolite weight ratios (>1.25 wt %), a second phase inversion occurs and creamy O/W HIPEs form through a different stabilization mechanism. In this case indeed, the zeolite particles are fully covered by a bilayer of TTAB and remain dispersed in the aqueous phase with no adsorption to the dodecane-water interface. The emulsion is stabilized by electrostatic repulsion between the highly positively charged zeolite particles and the cationic surfactant adsorbed at the dodecane-water interface.

Calcium ion effects on the water/oil interface in the presence of anionic surfactants

The influence of ion type at constant ionic strength on the surfactant layer present between a polar and a non-polar liquid has been investigated. The investigated systems are composed of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), dodecane and brines with different electrolyte compositions. Parallel and coordinated sampling have been performed via molecular dynamics simulation and experiments. By varying the molar ratio between calcium and sodium ions at constant ionic strength, we determined the relative influence of the bivalent ion. In the present work, firstly, we provide an atomistic description via molecular dynamics (MD) simulations of the surfactant and electrolyte distributions in respect to the dodecane-water interface. Secondly, we report the interfacial tension (IFT) and the estimated Debye length based on the theory of the electric double layer, comparing the simulation results with a classical interface description.

Two-Dimensional Electrochemiluminescence: Light Emission Confined at the Oil-Water Interface in Emulsions Stabilized by Luminophore-Grafted Microgels.

We describe a method to confine electrochemiluminescence (ECL) at the oil-water interface of emulsion droplets that are stabilized by luminophore-grafted microgels. These hydrogel nanoparticles incorporating covalently bound Ru(bpy)32+ as the luminophore are irreversibly adsorbed at the interface of micrometric oil droplets dispersed in a continuous aqueous phase. We study the electrochemical and ECL properties of this multiscale system, composed of a collection of droplets in close contact in the presence of two types of model coreactants. ECL emission is observed upon oxidation of the coreactant and of the luminophore. ECL imaging confirms that light is emitted at the surface of oil droplets. Interestingly, light emission is observed more than 100 μm far from the electrode. It is possibly due to the interconnection between redox-active microgels, making an entangled two-dimensional network at the dodecane-water interface and/or to some optical effects related to the light propagation and refraction at different interfaces in this multiphasic system. Confining ECL in such an inhomogeneous medium should find promising applications in the study of compartmentalized systems, interfacial phenomena, sensors, and analysis of single oil droplets.

Coarse-grained modeling of the oil–water–surfactant interface through the local definition of the pressure tensor and interfacial tension

Mesoscopic simulations are conducted to study the dodecane–water interface in the presence of an increasing quantity of sodium dodecyl sulfate. Dissipative Particle Dynamics and Molecular Dynamics using the MARTINI force field were used to model the dodecane–SDS–water system through a coarse-grained description. We have used a full description of the water and oil phases to study the structure of the interface. We have calculated the interfacial tension at the dodecane–water interface and established the accuracy of the calculation by checking the mechanical equilibrium and the stability of the interface. The local components of the pressure tensor are calculated along the interface by comparing both atomistic and molecular definitions. Both coarse-grained models give a good description of the system structure, with SDS molecules located at the interfaces. Increasing the number of SDS results in a drastic decrease in the interfacial tension and a saturation of the interface with SDS molecules. Higher SDS concentrations do not affect the interface structure, as it is saturated. The limiting value of the interfacial tension is very low and corresponds to the formation of a SDS film between the dodecane and water phases. Both coarse-grained potentials studied in this work are suitable for the study of surfactants in equilibrium with an oil–water interface. They provide a good description of the dodecane–SDS–water system and quantitative results for interfacial tension and interfacial concentrations. © 2017, Springer-Verlag Berlin Heidelberg.

Total Internal Reflection Magneto-optical Detection of Dysprosium(III) Ions Adsorbed at Liquid–Liquid Interface

Abstract A highly sensitive magneto-optical (MO) measurement technique was evaluated for the detection of interfacial species adsorbed at a flat liquid–liquid interface by using total internal reflection. The interfacial adsorption of the paramagnetic Dy(III) ion, which forms a complex with laurate at the dodecane–water interface, was detected with an extraordinarily large MO rotation angle.

Alignment and Chirality of Porphyrin J Aggregates Formed at the Liquid–Liquid Interface of a Centrifugal Liquid Membrane Cell

Previous direct observations of the J aggregates of diprotonated 5,10,15,20-tetraphenyl-21H,23H-porphine (H4TPP(2+)) formed at the dodecane-water interface in a centrifugal liquid membrane (CLM) cell using conventional CD spectroscopy have shown the existence of circular dichroic signals with a bisignated shape whose sign depends on the rotation direction of the cell. Herein we demonstrate that the determination of the optical Mueller matrix with a two-photoelastic modulator generalized ellipsometer (2-MGE), working in transmission mode, along with the assumption of a two superimposed twin Mueller matrices model (two opposite interfaces in the cylindrical rotation cell) allows us to infer the CD spectra due to overlapping linear polarizations from J aggregates at the front and back liquid-liquid interfaces in the rotating cell. The rotation direction dependence of the CD spectra was thoroughly interpreted by the present model considering the sign and the magnitude of the orientation angle between the front and back J aggregates. The present analysis should help us to understand the optical chirality due to the structural changes in supramolecular and macromolecular systems under flow shear forces as well as changes in birefringence.

Effect of Adsorbed Amphiphilic Copolymers on the Interfacial Activity of Superparamagnetic Nanoclusters and the Emulsification of Oil in Water

A series of sub-100 nm superparamagnetic iron oxide nanoparticles with amphiphilic poly(acrylic acid-b-butylacrylate); PAA-b-PBA) copolymer shells were synthesized and characterized by NMR spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and a superconducting quantum interference device (SQUID) to investigate the effect of the polymer structure on the interfacial tension for nanoparticles adsorbed at the dodecane-water interface. Large reductions in interfacial tension of up to 27.6 mN/m were measured at nanoparticle concentrations of 0.27 wt %, indicating significant nanoparticle adsorption and interaction between the oil and water molecules at the interface. The adsorption energy of the polymer-coated nanoparticles at the dodecane/water interface was determined from the interfacial tension and nanoparticle radius, and analyzed in terms of the structure of the polymer stabilizer. Furthermore, the equilibrium adsorption of amphiphilic copolymer-functionalized iron oxide nanoclusters at the oil–water interface was determined by material balance from the concentration in the excess water phase and the known overall oil/water interfacial area. The formation and stabilization of oil droplets were on the order of 10 μm in water with unusually low nanoparticle concentrations was explained in terms of the high interfacial activity of the particles.

Chiral recognition of 2-alkyl alcohols with porphyrin J-nanoaggregates at the liquid–liquid interface

The J-aggregate of diprotonated tetraphenylporphyrin (H(4)TPP(2+)) formed at the dodecane-water interface showed circular dichroism spectra corresponding to the chirality of 2-alkyl alcohols, longer than 2-butanol, added to the dodecane phase. The phenomenon suggested the preferential interaction between the nano-sized J-aggregates and the chiral alcohols at the interface, and provided a potential use of the J-nanoaggregate as a chiral recognition probe.

Wetting Properties of Passivated Metal Nanocrystals at Liquid−Vapor Interfaces: A Computer Simulation Study

Molecular dynamics simulations have been employed to determine the contact angles of alkylthiol passivated gold nanocrystals adsorbed at the air-water interface. Simulations were performed using butane-, dodecane-, and octadecanethiol passivated nanoparticles. We demonstrate how the length of the surfactant chain can profoundly influence the wetting behavior of these nanoparticles. All particles were found to be stable at the air-water interface, possessing large, well-defined contact angles. We find that the shape of the dodecane- and octadecanethiol particles is strongly perturbed by the interface. We also present an analysis of the orientational ordering of water molecules at the dodecane-water interface and around butane- and dodecanethiol passivated nanoparticles. The orientational ordering translates into an electrostatic field around the nanoparticles, the magnitude of which corresponds with that of the water liquid-vapor interface.

Dynamic surface properties, wettability and mimic oil recovery of ethanediyl- α, β -bis(cetyldimethylammonium bromide) on dodecane modified silica powder

In order to increase petroleum oil recovery, the wettability of the interface between flooding aqueous solution and oil reservior plays an important role. A surfactant dissolved in the flooding solution can be adsorbed on the reservior surface and then the wettability of the interface can be changed. For the purpose of mimic oil recovery, a cationic gemini surfactant, ethanediyl-α, β -bis(cetyldimethylammonium bromide) (16-2-16), was synthesized and characterized. The dynamic surface and interface tensions have been measured using pendant drop method at the air-water surface and dodecane-water interface, and experimental curve is close to orientation model and interaction model of surface equations of state. Compared with conventional cationic surfactants, cetyldimethylammonium bromide (CTAB), 16-2-16 has very low cmc value (1.8 × 10− 5 mol/L to 1.0 × 10− 3 mol/L). The most hydrophilic condition between the surfactant aqueous solution and the silica powder surface appears near the cmc for both 16-2-16 and CTAB. The best mimic oil recovery is also reached around the cmc for the two surfactants, but the efficiency for the former (68%) is higher than the one for the latter (63%).

Magnetic Field Enhanced Microextraction Rate of Europium(III) with 2-Thenoyltrifluoroacetone and Oxalate at Dodecane-Water Interface

A microscopic system for the observation of reactions at a liquid-liquid interface was established, to which strong magnetic fields (0-0.4 T) could be applied with permanent magnets. In situ observation for the interfacial extraction of fluorescent and paramagnetic Eu(III) ion with 2-thenoyltrifluoroacetone (Htta) in dodecane was carried out. In the presence of oxalate (ox2-), micro-aggregates of Eu(III)-tta-ox complexes were generated in the aqueous phase before its extraction. When the micro-aggregates diffused to the dodecane-water interface, Eu(tta)3 was extracted with excess Htta in the dodecane phase. The microextraction process of the aggregates was observed as random flashes of Eu(tta)3 fluorescence at the dodecane-water interface. The single flash contained about 10(-16)-10(-14) mol of Eu(III). An application of magnetic fields made the flash frequency increase, which corresponded to an enhancement of interfacial Eu(III) extraction rate. The enhancement effect was attributable to the magnetophoresis of the paramagnetic microaggregates to the dodecane-water interface.

Dynamic Microscopic Extraction of Europium(III) with 2-Thenoyltrifluoroacetone Observed as Random Fluorescence Flashes at Dodecane–Water Interface

Abstract Many random circular flashes of Eu(III) fluorescence (8–23 μm in diameter) appeared at the interface in the extraction of Eu(III) with 2-thenoyltrifluoroacetone (Htta) into dodecane, when a Eu3+ aqueous solution was added after pre-distribution of Htta in the aqueous phase. The flash was caused by the interfacial reaction between a pre-generated micro-aggregate of Eu(tta)2+ in the aqueous phase and excess Htta in the dodecane phase. The interfacial reaction produced more fluorescent Eu(tta)3, which diffused away into the dodecane phase.

Single Molecule Detection of Cyanine Dye at the Dodecane-Water Interface

Single Molecule Detection of Cyanine Dye at the Dodecane-Water Interface

Heterogeneous Fluorescence Quenching Reaction between (5,10,15,20-Tetraphenylporphyrinato)zinc(II) and Methylviologen at Dodecane-Water Interface

Abstract The heterogeneous fluorescence quenching reaction of (5,10,15,20-tetraphenylporphyrinato)zinc(II) (ZnTPP) in dodecane by methylviologen in an aqueous phase at the liquid-liquid interface was investigated by means of the centrifugal liquid membrane method. The quenching reaction could occur only in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). The quenching efficiency depended on the concentration of SDS in the aqueous phase with a maximum value of 13.5%.