Oil Interface Research Articles

Coarse-Grained Interface Surfactant Density Maps for Calculation of the Fractional Conversion of Tetrameric Carboxylic Acids to Calcium Naphthenate Precipitates

Modeling molecular interactions on different length scales is often necessary and presents a significant challenge in chemical engineering. In the present study, we apply molecular dynamics (MD) simulations on different tetrameric carboxylic acid (TA) molecules absorbed at a water–oil interface, which tend to form a cross-linked network in the presence of calcium. From the MD simulations, we obtain various spatial probabilities describing the molecular geometries of TAs in the interfacial region. The MD-obtained probability distribution functions are then used to recreate a coarse-grained representation (interface map) of the interfacial density of the TA molecules. The interface maps are created by randomly placing molecules in an interfacial region and calculating the coordinates of the carboxylate groups according to the MD probability functions. By creating a large number of interface maps, we can obtain a better statistical representation of how the molecules are spatially arranged at the interface a...

Luminescent and absorptive metal-coated emulsions for micro-velocimetry

Fluorescent latex beads have been widely used as tracers in microfluidics for the last decades. They have the advantages to be density matched with water and to be easily localizable using fluorescence microscopy. We have recently synthesized silver-coated oil droplets that are both luminescent and absorptive, by first coating the oil interface with a polydopamine layer and then depositing a silver layer by a redox process. They have a mean diameter of 6μm and their density has been matched to the density of water by adjusting the thickness of the metallic layer. In this work we used these particles as tracers to measure the velocity profile of an aqueous solution in a PDMS microchannel with a rectangular cross-section. This allowed us to confirm the predictions of the Stokes equation with results comparable to those of common polystyrene particles.

Microscopic Study of Wax Deposition: Mass Transfer Boundary Layer and Deposit Morphology

This study presents a pioneering effort to enable visualization of the in situ wax deposition process in a microscopic scale with an emphasis on mass transfer boundary layer and deposit morphology observations. The mass transfer boundary layer study validates the existence of partial wax supersaturation near the wax deposit and oil interface. The discrepancy between the actual mass transfer boundary layer thickness and the heat–mass transfer analogy prediction expands as the Reynolds number increases and the ΔT (temperature difference between the bulk and cold interface) decreases. This conclusion is in agreement with several flow loop data with the same oil and similar flowing conditions. The morphology study reveals that, under laminar conditions, the distribution of the deposit crystal aspect ratio resembles a log-normal pattern with a distribution mode between 2 and 3. This characteristic exhibits similarity with wax crystals observed under static cooling conditions. Deposits formed under laminar cond...

Dynamic behavior of air–oil interface in fluid dynamic bearings with a double sealing structure in a 2.5′′ hard disk drive due to non-operating axial shock

We propose a numerical procedure to investigate the oil leakage of FDBs with a double sealing structure in a 2.5′′ HDD due to non-operating axial shock. We confirm the validity of the proposed procedure via a drop test to observe oil leakage of FDBs from the motion of rotor and stator under axial shock. We simulate the two-phase flow of air and oil in FDBs using a finite-volume method and a volume of fluid method to investigate the unsteady motion and break-up of the air–oil interfaces during and after axial shock. Furthermore, we analyze the axial shock-induced motion of air–oil interfaces due to magnitude of shock, and various design variables of the FDBs and the capillary seal.

Graphical estimation of interface mass-transfer coefficient (k) using pressure-decay data

A new graphical procedure is proposed to estimate the interface resistivity in terms of interface mass-transfer coefficient (k) in gas–oil pressure decay experiments. We provide a time-domain closed-form analytical solution by the use of Integral Method (IM) to the equations governing the gas-phase-pressure decay with the improved time-dependent gas–oil interface boundary condition. A graphical technique, derived from this analytical solution, is proposed to extract the interface mass-transfer coefficient and Henry׳s constant. Application of this method to synthetic and experimental pressure-decay data shows that the estimated parameters are in agreement with those reported in the literature. The proposed procedure, coupled with a graphical technique to estimate the diffusion coefficient, is an asset for a simple, quick, and reliable estimation of interface mass-transfer coefficient and Henry’s constant.

Analytical Solutions and Derivation of Relative Permeabilities for Water-Heavy Oil Displacement and Gas-Heavy Oil Gravity Drainage Under Non-Isothermal Conditions

Summary Analytical models were developed for non-isothermal gas/heavy-oil gravity drainage and water-heavy oil displacements in round capillary tubes including the effects of a temperature gradient throughout the system. By use of the model solution for a bundle of capillaries, relative permeability curves were generated at different temperature conditions. The results showed that water/gas-heavy oil interface location, oil-drainage velocity, and production rate depend on the change of oil properties with temperature. The displacement of heavy oil by water or gas was accelerated under a positive temperature gradient, including the spontaneous imbibition of water. Relative permeability curves were greatly affected by temperature gradient and showed significant changes compared with the curves at constant temperature. Clarifications were made as to the effect of variable temperature compared with the constant (but high) temperatures throughout the bundle of capillaries.

YAG Membranotomy for Persistent Postoperative Fibrinous Pupillary Membrane in an Aphakic Patient with Silicone Oil

We report a case of using Nd:YAG laser to perform a membranotomy of a persistent dense fibrinous pupillary membrane at the silicone oil (SO) interface in an aphakic patient following pars plana vitrectomy (PPV), pars plan lensectomy(PPL) with SO placement. Nd:YAG laser was successfully used to create a central opening in the fibrinous membrane at the SO interface which allowed for the proper examination of the posterior segment and improvement in the patient’s visual acuity.

NRET — A rapid method to investigate the water–oil interface in reverse micellar systems

The water–oil interface of AOT/water/isooctane reverse micelles, with different hydration degrees (w0), is investigated by nonradiative energy transfer (NRET) between naphthalene (Np) probe and pyrene grafted poly(acrylic acid) (PAA150-Py32). The polymer is water-soluble while Np has affinity for the organic solvent. UV–Vis spectroscopy reveals that PAA150-Py32 is constrained in the micellar nanocage. The change of the pH of the micellar core and the addition of electrolyte are considered. FTIR and static fluorescence measurements confirm the presence of the polymer at the micellar interface. The stability and size distribution of the reverse micelles, with or without PAA150-Py32 and electrolyte are characterized by DLS. The photophysical parameters of PAA150-Py32 (the polarity index, I1/I3 and the polymer conformation index, IE/IM) are determined at different pHs and electrolyte concentrations. For w0=10 and w0=15, the pH does not influence the formation of Py excimers, which is an atypical behavior. NRET is strongly dependent on the pH, and for w0=10 and pH=3.6 it reaches a maximum. The optimal salt concentration for which NRET is maximal is 5×10−4M NaCl. The acquired results shed more light upon the stability of the micellar interface in various experimental conditions.

Interfacial Effects on the Spherulitic Morphology of Isotactic Polystyrene Thin Films on Liquid Substrates

The influence of interfaces on the morphology of flat spherulites of isotactic polystyrene (iPS) grown in thin films on liquid substrates was investigated. Amorphous iPS thin films spin-cast from a solution were annealed for cold crystallization on glycerol and silicone oil (nonsolvents for iPS). The number density of grown spherulites was revealed to be higher on the glycerol substrate than on the silicone oil substrate. This implies that the primary nucleation rate of crystallization is greater at the iPS/glycerol interface than at the iPS/silicone oil interface. The results may be consistent with the previous findings that concern the molecular interaction between atactic polystyrene and nonsolvents at the interface. In some cases, holes were formed in the thin films during the cold crystallization due to dewetting, which also significantly affect the spherulite morphology via, for example, transcrystallization.

Distribution of Triamcinolone Acetonide after Intravitreal Injection into Silicone Oil-Filled Eye.

There is increasing use of the vitreous cavity as a reservoir for drug delivery. We study the intraocular migration and distribution of triamcinolone acetonide (TA) after injection into silicone oil tamponade agent during and after vitrectomy surgery ex vivo (pig eye) and in vitro (glass bottle). For ex vivo assessment, intraocular migration of TA was imaged using real-time FLASH MRI scans and high-resolution T2W imaging and the in vitro model was monitored continuously with a video camera. Results of the ex vivo experiment showed that the TA droplet sank to the interface of silicone oil and aqueous almost immediately after injection and remained inside the silicone oil bubble for as long as 16 minutes. The in vitro results showed that, after the shrinkage of the droplet, TA gradually precipitated leaving only a lump of whitish crystalline residue inside the droplet for about 100 minutes. TA then quickly broke the interface and dispersed into the underlying aqueous within 15 seconds, which may result in a momentary increase of local TA concentration in the aqueous portion and potentially toxic to the retina. Our study suggests that silicone oil may not be a good candidate as a drug reservoir for drugs like TA.

Instability-Induced Mixing of Ferrofluids in Uniform Magnetic Fields

The advantages of ferrofluids in microfluidic lab-on-a-chip applications include remote control of the fluid flow within the chips, e.g., mixing of the species using an external uniform magnetic field. Hence, three-stream flow systems consisting of a ferrofluid core clad by two streams of diamagnetic silicone oil were studied. The instability of the ferrofluid, subjected to an external uniform magnetic field, was also studied. When the strength of this magnetic field was increased to a critical value, the ferrofluid was spread toward the silicone oil and a transient instability developed at the ferrofluid–silicone oil interface. Further increasing magnetic field resulted in periodic instability structures and permanent instability. The effect of magnetic field strength, flow rate, and flow rate ratio were determined. With a higher flow rate ratio, the permanent instability was observed only at the larger magnetic field strength. Our modeling results were consistent with these experimental results. Our work shows that an external uniform magnetic field of only a few millitesla can lead to instability and mixing, thus it is relevant to mixing in practical microfluidic devices.

Interfacial rheometry of polymer at a water-oil interface by intra-pair magnetophoresis.

We describe an interfacial rheometry technique based on pairs of micrometer-sized magnetic particles at a fluid-fluid interface. The particles are repeatedly attracted and repelled by well-controlled magnetic dipole-dipole forces, so-called interfacial rheometry by intra-pair magnetophoresis (IPM). From the forces (∼pN), displacements (∼μm) and velocities (∼μm s(-1)) of the particles we are able to quantify the interfacial drag coefficient of particles within a few seconds and over very long timescales. The use of local dipole-dipole forces makes the system insensitive to fluid flow and suited for simultaneously recording many particles in parallel over a long period of time. We apply IPM to study the time-dependent adsorption of an oil-soluble amino-modified silicone polymer at a water-oil interface using carboxylated magnetic particles. At low polymer concentration the carboxylated particles remain on the water side of the water-oil interface, while at high polymer concentrations the particles transit into the oil phase. Both conditions show a drag coefficient that does not depend on time. However, at intermediate polymer concentrations data show an increase of the interfacial drag coefficient as a function of time, with an increase over more than three orders of magnitude (10(-7) to 10(-4) N s m(-1)), pointing to a strong polymer-polymer interaction at the interface. The time-dependence of the interfacial drag appears to be highly sensitive to the polymer concentration and to the ionic strength of the aqueous phase. We foresee that IPM will be a very convenient technique to study fluid-fluid interfaces for a broad range of materials systems.

Oil/Water Nanoemulsions: Activity at the Water–Oil Interface and Evaluation on Asphaltene Aggregates

Oil-in-water (O/W) nanoemulsions based on nonionic ethoxylated polymeric surfactants were prepared and evaluated for demulsification of water/oil emulsions and model asphaltene emulsions. The nanoemulsions were prepared using two nonionic ethoxylated polymeric surfactants with different numbers of ethylene oxide units in their chains and the solvents xylene and Solbrax as the oil phase, at different concentrations. The interfacial properties of the different systems applied in the demulsification process were evaluated in model emulsions and were correlated with their ability and/or speed of diffusion to the interface. Tests of asphaltene dispersion/flocculation were performed to evaluate whether the nanoemulsions change the aggregation state of asphaltenes during the demulsification process. The results of gravitational separation tests showed that the new nanoemulsion formulations studied can be applied to demulsify water/oil emulsions. Both the type of polymeric surfactant used and the type and content...

Spontaneous Formation of Nano-Emulsions Containing Task-Special Ionic Liquid and CO2 Capture in this Nano-Emulsions System

Nano-emulsions containing task-special ionic liquid ([NH2ebim][PF6]) were prepared by spontaneous emulsification. The stability of nano-emulsions was investigated by analysis of droplet size. The microstructure of the mixed solvent including the Triton X-100, n-butanol, and [NH2ebim][PF6] was demonstrated based on macular dynamic simulation. The results indicate that nano-emulsions are relatively stable to the droplet growth at static storage, but unstable under high centrifugal force. Simulation results from the macular dynamic calculation show that [NH2ebim][PF6] locates in the hydrophobic layer of Triton X-100 and n-butanol, which is available for enhancing CO2 mass transfer in an absorption process. Nano-emulsions were used as the absorbent to absorb CO2 in absorption experiments, and the absorption rates were investigated. The results show that nano-emulsion containing [NH2ebim][PF6] can enhance CO2 absorption rate compared to the system that pure water was used as the absorbent. The reason is attributed to the reversible chemical reaction between [NH2ebim][PF6] and CO2 on the interface of oil and water, which decreases the concentration of CO2 in the bulk so as to increase the mass transfer driving force between gas and liquid. Therefore, the chemical reaction on the interface of oil and water promotes the absorption process.

Reduction in interfacial tension of water–oil interface by supercritical CO2 in enhanced oil recovery processes studied with molecular dynamics simulation

The interfacial tension (IFT) has a significant influence on fluid flow in the supercritical CO2 (scCO2) enhanced oil recovery process. However, it is still challenging to demonstrate the effect of scCO2 on water–oil interface. Therefore, a molecular dynamics simulation is performed to investigate the influence of scCO2 on the water–decane interface. It is observed that CO2 prefers to accumulate and display surface-active at the water–decane interface. The driving force of CO2 accumulation is the IFT difference between water–decane and water–CO2. The IFT of water–CO2–decane decreases linearly with the increase of CO2. The interactions of water–CO2 and decane–CO2 are strong, and the difference between them is small, providing the mechanism for lowering the IFT of water–decane. The increase in the diffusivity for all fluids toward the interface suggests an increase in the mobility at the water–decane interface due to the addition of CO2, which is in favor of enhancing oil recovery.

Viscosity Measurement in a Lubricant Film Using an Ultrasonically Resonating Matching Layer

A novel ultrasonic viscometer intended for in-situ applications in lubricated components is presented. The concept is based on the reflection of a shear wave at a solid–liquid boundary that depends on the viscosity of the liquid and the acoustic properties of the solid. Very little ultrasound energy can propagate into the oil at a metal–oil interface because the acoustic mismatch is great, and this leads to large measurement errors. The method described in this paper overcomes this limitation by placing a thin intermediate matching layer between the metal and the lubricant. Results obtained with this technique are in excellent agreement with expected values from conventional viscometers when Newtonian mineral oils are analysed. When complex non-Newtonian mixtures are tested, the viscosity measurement is frequency dependent. At high ultrasonic frequencies, over 1 MHz, it is possible to shear only the base oil, while to obtain the viscosity of the mixture it is necessary to choose a lower excitation frequency to match the dispersed polymer relaxation time.

Adsorption and isolation of nucleic acids on cellulose magnetic beads using a three-dimensional printed microfluidic chip

While advances in genomics have enabled sensitive and highly parallel detection of nucleic acid targets, the isolation and extraction of the nucleic acids remain a critical bottleneck in the workflow. We present here a simple 3D printed microfluidic chip that allows for the vortex and centrifugation free extraction of nucleic acids. This novel microfluidic chip utilizes the presence of a water and oil interface to filter out the lysate contaminants. The pure nucleic acids, while bound on cellulose particles, are magnetically moved across the oil layer. We demonstrated efficient and rapid extraction of spiked Human Papillomavirus (HPV) 18 plasmids in specimen transport medium, in under 15 min. An overall extraction efficiency of 61% is observed across a range of HPV plasmid concentrations (5 × 10(1) to 5 × 10(6) copies/100 μl). The magnetic, interfacial, and viscous drag forces inside the microgeometries of the chip are modeled. We have also developed a kinetics model for the adsorption of nucleic acids on cellulose functionalized superparamagnetic beads. We also clarify here the role of carrier nucleic acids in the adsorption and isolation of nucleic acids. Based on the various mechanistic insights detailed here, customized microfluidic devices can be designed to meet the range of current and emerging point of care diagnostics needs.

Gold Nanofilm Redox Catalysis for Oxygen Reduction at Soft Interfaces

The interfacial reduction of oxygen by a lipophilic electron donor, decamethylferrocene, dissolved in α,α,α-trifluorotoluene was catalyzed at a gold nanoparticle nanofilm modified water–oil interface. A recently developed microinjection technique was utilized to modify the interface reproducibly with the mirror-like gold nanoparticle nanofilm, while the oxidized electron donor species and the reduction product, hydrogen peroxide, were detected by ion transfer voltammetry and UV/vis spectroscopy, respectively. Metallization of the soft interface allowed the interfacial oxygen reduction reaction to proceed via an alternative mechanism with enhanced kinetics and at a significantly lower overpotential in comparison to a bare soft interface. Weaker lipophilic reductants, such as ferrocene, were capable of charging the interfacial gold nanoparticle nanofilm but did not have sufficient thermodynamic driving force to significantly elicit interfacial oxygen reduction.

Gas hydrate plug formation in partially-dispersed water–oil systems

The formation of gas hydrate plugs in deep water oil and gas flowlines poses severe operational and safety hazards. Previous work has established a mechanism able to describe plug formation in oil-continuous systems, which relies on the assumption that all the water remains emulsified in the oil phase. However, light hydrocarbon fluids, including condensates, may not stabilize water-in-oil emulsions, and the current mechanistic model cannot reliably assess the risk of plug formation in this scenario. This study presents a comprehensive set of experiments conducted in a high-pressure sapphire autoclave apparatus using 10 to 70vol% water in partially-dispersing mineral oil at three fixed rotational speeds: 300, 500 and 900RPM. Pressure and temperature were monitored continuously in the autoclave, providing direct estimates of hydrate growth rate, alongside measurements of the motor torque required to maintain constant mixing speed. A new conceptual mechanism for plug formation has been developed based on the visual observations made during these experiments, where a small hydrate fraction (2–6vol%) in the oil phase was observed to disrupt the stratified water–oil interface and help disperse the water into the oil. This disruption was followed by an increase in the hydrate growth rate and particle agglomeration in the oil phase. In the final stages of hydrate growth for systems with low turbulence and high watercut, hydrate particles in the visual autoclave were observed to form a moving bed followed by full dispersion of water and oil, rapid hydrate growth and deposition on the wall. These rapid hydrate growth and deposition mechanisms significantly increased the maximum resistance-to-flow for partially-dispersing systems in comparison with mixtures that are fully dispersed under similar conditions.

Effects of pH and salinity on adsorption of different imidazolium ionic liquids at the interface of oil–water

Adsorption and micelle formation of six short and long alkyl chain imidazolium ionic liquids (ILs), [Cnmim][X] with n = 6–8, 12, 16 and X = Cl−, Br−, were studied at toluene–water interface under different pHs (within 5.5–8.5) at 298.2 K. Further, the adsorption of long alkyl chain ILs (n = 12 and 16) was explored in presence of different uni-univalent salts at the same temperature. By the adsorption of each IL having different alkyl chain length or different anions at the interface, interfacial tension (IFT) decreased and ultimately micelles formed. Interestingly, increase in aqueous phase pH or salinity intensified the reduction in the IFT and CMC values. Experimental data, relevant to concentrations below the CMCs, were satisfactorily reproduced by Frumkin adsorption isotherm and parameters were obtained. For each IL, by rising pH, adsorption equilibrium constant and maximum interface excess increased and interaction parameter tended to positive values because of hydroxyl anion adsorption along with cationic portion of ILs. Besides, the presence of uni-univalent electrolytes caused increase the adsorption equilibrium constant and maximum interface excess to achieve due to salting out effect.