Aqueous Phase Droplets Research Articles

Effectiveness and limitations of two drop studies to explain emulsion dehydration under modulated electric fields

AbstractElectrocoalescence has long been known for the separation of a water‐in‐oil emulsion. An associated challenge with electrocoalescers is the undesired noncoalescence and consequently chain formation of aqueous phase droplets. This leads to low separation efficiency and damage of electrical equipment. Recently Hasib et al. proposed an electric field modulated scheme that showed significant improvement in dehydration of water‐in‐oil emulsions. They investigated the range of modulation parameters when the scheme is most effective. The fundamental process in electrostatic dehydration of an emulsion is the interaction between a pair of water droplets. In the present study, two suspended aqueous drops in insulated oil experiments are compared for their behavior under unmodulated and modulated electric fields. Further, a model is developed and the experimental behavior under unmodulated and modulated electric fields is compared with numerical solutions. The model predicts the experimental observations accurately by balancing electrostatic, electrophoresis, dipolar, and resisting viscous drag forces, ignoring the end (bridge) effect during the contact. The study shows that the increase in the rate of dehydration of a water‐in‐oil emulsion under modulated electric fields with an increase in duty ratio and its near independence on the modulation time period can be explained by the two‐drop studies. However, several other processes such as multidrop interactions as well as scavenging of fine droplets by charged droplets created as intermediates in the interaction of two droplets cannot be explained by the two‐drop studies.

Quasi-3D visualization and local parameter measurement of horizontal and nearly horizontal liquid–liquid two-phase flows by using PLIF method

Horizontal and nearly horizontal liquid–liquid two-phase flows are widely encountered in petroleum, chemical, and other important industrial production fields. The three-dimensional (3D) flow visualization and the local parameter measurement are of great significance for understanding the flow dynamics and revealing the flow-pattern transition mechanism. In this paper, experiments of horizontal and nearly horizontal (+5°) liquid–liquid flow are carried out in an acrylic pipe with an inner diameter of 20 mm. Silicone oil (organic phase) and water/glycerol mixture (aqueous phase) are used as the test fluid. A novel planar laser-induced fluorescence (PLIF) system is designed to detect the flow structures. The incident direction of the laser sheet is along the radial section of the pipe, and the PLIF camera is positioned at 60° to the plane of the laser sheet, referred to as PLIF-60. In the experiment, the two-dimensional (2D) flow images at the pipe radial section are captured by the PLIF-60 system. Considering the effect of the angle between the laser sheet and the PLIF camera, the flow images are corrected to remove the horizontal and vertical distortions. The liquid–liquid stratified interface and the entrained droplets are identified in the corrected flow images. A droplet tracking method is proposed to derive the droplet diameter and its quantity distribution. Quasi-3D flow structures are reconstructed upon the accurate detection of the stratified interface and the entrained droplets. The evolution characteristics of the interface structures and the spatial distributions of droplets are studied. In addition, aqueous phase holdup and droplet entrainment ratios at pipe axial and radial sections are extracted based on the quasi-3D flow visualizations. The effects of the flow conditions and the pipe inclinations on the profiles of the aqueous phase holdup and the droplet entrainment ratio are uncovered.

Systematic study on interfacial polymerization mechanism of toluene diisocyanate and water for the preparation of polyurea microspheres

• Droplets-based microfluidics is used to generate TDI droplets in aqueous phase. • Polyurea microspheres were prepared by interface polymerization of TDI with water. • Interface polymerization mechanism of TDI with water is studied in details. Polyureas (PU) are important materials in wide range of applications from protective coatings and catalyst supports to biomaterials for drug release and hydrogels. However, it has been a challenging task to prepare porous PU with definite form or shape limited by the nature of the PU synthesis, that is, precipitation polymerization. New chemical and physical techniques of PU synthesis have gained great attention in order to fabricate these materials with diverse morphologies and structural features. In this communication, droplet-based microfluidics approach is adopted to convert conventional precipitation polymerization of PU synthesis to interface polymerization and PU microspheres with porous morphology are prepared. In this process, first toluene diisocyanate (TDI) droplets were generated in flowing PVA aqueous solution inside a tube and then converted to uniform porous PU microspheres through interface polymerization. The interface polymerization mechanism is discussed in details by controlling the polymerization time. It was found that polymerization of TDI with water was started at the interface of TDI droplet and water, and PU shell was formed around the TDI droplets, leading to formation of microcapsules. After the formation of PU shell, polymerization was continued inside the microcapsule by the diffusion of water molecules through the PU shell until all the TDI was finished and PU microspheres with porous morphology were obtained. This communication provides therefore a systematic study on interfacial polymerization of TDI with water to get porous PU microspheres and enabling technical advantages for potential applications to get PU materials with specific shapes and textural modifications.

Microemulsions; A Mini Review

The review goes into great detail about the microemulsions' characteristics, structure, kinds, theories, characterization, and applications. They may be made easily by mixing the various ingredients together without the need for special tools or circumstances. Unlike the o/w type microemulsion, which has an aqueous continuous phase and oil droplets distributed in it, the w/o type microemulsion has oil as the continuous phase and water as droplets are disseminated in it. Microemulsions are classified into four primary categories based on different phase systems, and they are often utilized in the pharmaceutical and cosmetics sectors as well as in analytical methods. The design of medicine formulations and cosmetics may benefit from having a thorough understanding of the physicochemical and biological characteristics of microemulsions.

Modeling of fouling mechanisms in the biodiesel purification using ceramic membranes

Since membrane fouling is well acknowledged to be one of the key impediments to more widespread implementation of membrane-filtration processes, this study aimed to assess the fouling mechanisms in the biodiesel separation and purification process using ceramic membranes. The analysis of fouling mechanisms was performed using a model proposed in the literature applied to cross-flow filtration and constant pressure. The experiments were carried out with tubular ceramic membranes with average pore size of 0.2 µm, 0.1 µm, 0.05 µm, and 20 kDa at 1.0, 2.0, and 3.0 bar transmembrane pressures. After transesterification, the reaction mixture was directly processed, eliminating the conventional previous decantation step. It was evaluated the influence of acidified water addition (10, 20 and 30 wt%) on the glycerol retention efficiency and the fouling mechanism. The results obtained demonstrated that the amount of water added influences the formation of the phases and, consequently, the separation performance. The permeate flux profile over time made it possible to determine the predominant fouling mechanism in each evaluated condition. Thus, the predominant fouling mechanisms were complete pore blocking, cake filtration and internal pore blocking when using 10, 20 and 30% water concentration, respectively. It was possible to conclude that the fouling mechanism dominant in each experimental condition is dependent upon the size of aqueous phase droplets and the membrane pore diameter. The results demonstrated that it would be possible to predict the efficiency of glycerol separation by identifying the fouling mechanism, so that the condition of complete pore blocking is the most recommended in this biodiesel purification process, since it indicates a greater retention of glycerol by the membrane, and the stabilization of fluxes at higher rates.

L–Arginine and l–Lysine improve the physical stability of soybean oil–myosin emulsions by changing penetration and unfolding behaviors of interfacial myosin

This study investigated the mechanisms underlying the influence of l–Arginine (Arg)/l–Lysine (Lys) on the physical stability of soybean oil–myosin emulsions (SOME). Results indicated that Arg and Lys increased emulsifying activity index and emulsifying stability index, but decreased the residual protein content in the aqueous phase, CI and oil droplet size of SOME. Arg increased the interfacial pressure (π) of SOME and increased the penetration rate (kP) but decreased the diffusion rate (kdiff) of interfacial myosin. Lys increased the kP but decreased the kdiff of the interfacial myosin and decreased the π of SOME. Lys reduced the rearrangement rate of interfacial myosin; Arg only slightly affected it. Lys was more effective than Arg in exposing tyrosine and tryptophan residues of interfacial myosin; Arg was more conducive than Lys for structurally transforming interfacial myosin from disordered to ordered. These results confirm that Arg and Lys changed the structure and penetration of interfacial myosin, improving the physical stability of SOME.

Equilibrium and dynamic interfacial tensions of oil/water in the presence of an imidazolium ionic liquid strengthen with magnetite nanoparticles

This study explored the effect of [C12mim][Cl] ionic liquid on the equilibrium and dynamic interfacial tensions (IFTs) of n-heptane/water as a typical demonstrative model of oil/water system. The IL and the magnetite nanoparticles were synthesized and characterized in different ways including FTIR, 1HNMR, 13CNMR, mass spectrometry, SEM, TEM, DLS and XRD. The ionic liquid by itself caused an IFT reduction of 85.3% at critical micelle concentration of 0.025 mol/L and presence of nanoparticles intensified this effect, stronger under alkaline pHs. It was while nanoparticles alone had no considerable effect. The results of equilibrium IFT were nicely fitted with the Szyszkowski equation, and corresponding parameters were obtained. From dynamic IFT variations, it was found that the ionic liquid migration was adapted with the mixed diffusion from bulk to the interface. Therefore, the apparent diffusivity and the activation energy were obtained. Also, the stability of oil/water emulsions was increased in the simultaneous presence of the IL and nanoparticles. Confirming the results, the static contact angle of aqueous phase droplets surrounded by organic phase on the surface of quartz was raised in the presence of nanoparticles.

Statistical approach to estimate coalescence of a single droplet at interface affected by aqueous phase composition

A significant portion of the world's crude oil is produced in the form of oil-water emulsions. The effective separation of oil and water dispersions could be considered as one of the critical steps in determination of the economic and technical success of the petroleum industry for many years. Deep understanding of basic droplet coalescence at the interface and different parameters that are effecting on this phenomenon is essential for characterization of the global phase separation.An experimental investigation of the coalescence of single droplet at the interface of Exxsol-aqueous phase was carried, with emphasis on the effect of aqueous phase composition and droplet size on stability of droplets. A Coalescence Time Measurement (CTM) facility is utilized to measure mean coalescence time at the liquid-liquid interface and examine how it could be affected by droplet size, viscosity of the continuous phase and the composition of aqueous phase, which is crucial for characterization of the global separation process.Moreover statistical analysis of CTM data is conducted to develop relationship among the coalescence time and process controllable variables (droplet size, continuous phase viscosity, interfacial tension, density of dispersed phase and continuous phase, salinity and hydrate inhibitor concentration).

Interfaces Charged by a Nonionic Surfactant.

Highly hydrophobic, water-insoluble nonionic surfactants are often considered irrelevant to the ionization of interfaces at which they adsorb, despite observations that suggest otherwise. In the present study, we provide unambiguous evidence for the participation of a water-insoluble surfactant in interfacial ionization by conducting electrophoresis experiments for surfactant-stabilized nonpolar oil droplets in aqueous continuous phase. It was found that the surfactant with amine headgroup positively charged the surface of oil suspended in aqueous continuous phase (oil/water interface), which is consistent with its basic nature. In nonpolar oil continuous phase, the same surfactant positively charged the surface of solid silica (solid/oil interface) which is often considered acidic. The latter observation is exactly opposite to what the traditional acid-base mechanism of surface charging would predict, most clearly suggesting the possibility for another charging mechanism.

Efficient extraction and stripping of Nd(III), Eu(III) and Er(III) by membrane dispersion micro-extractors

The extraction of low concentration rare earth elements at high phase ratio was investigated. The traditional extraction set-up, such as mixer-settler, have drawbacks of easy emulsification, difficult separation and low efficiency if operated at the above condition. Membrane dispersion micro-extractor, owing to its well-dispersed, high surface-to-volume ratio and fast mass transfer rate, was employed in our work. Nd(III), Eu(III), Er(III) were chosen to represent light, medium, heavy rare earth elements (REEs). The extraction process of REEs with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) was investigated by membrane dispersion micro-extractors. Firstly, the extraction equilibrium of these three elements was explored in the stirred conical flasks, and it is indicated that the extraction efficiencies can be 0.95, 0.97 and 0.98, respectively within 40 min at phase ratio of 100:1. Then the effects of operational conditions such as the residence time, organic and aqueous flow rates on extraction efficiency were also explored in micro-extractors. The results indicate that the efficiency decreases and then increases if increasing aqueous phase flow rate, residence time and droplets' diameter are the key factors of this process. Increasing the phase ratio reduces the extraction efficiency significantly. When the REEs solution has an initial pH of 4.00, the flow rates of continuous and dispersed phase are 40 and 1.6 mL/min, respectively, and 90 mg/L Nd (III), Eu(III) and Er(III) is extracted by 1 mol/L P507 at the out-let length of 8 m. The extraction efficiencies are 0.978, 0.983 and 0.991, respectively. Finally the stripping process was also studied with the micro-extractor. The stripping efficiencies of Nd(III), Eu(III) and Er(III) can reach 0.99, 0.96 and 0.91, respectively when the out-let length is 8 m and the concentration of hydrochloric acid is 1 mol/L. The developed approach offers a novel and simple strategy on the fast extraction and enrichment of low concentration rare earth elements from waste water.

Microfluidic Droplet Extraction by Hydrophilic Membrane.

Droplet-based microfluidics are capable of transporting very small amounts of fluid over long distances. This characteristic may be applied to conventional fluid delivery using needles if droplets can be reliably expelled from a microfluidic channel. In this paper, we demonstrate a system for the extraction of water droplets from an oil-phase in a polymer microfluidic device. A hydrophilic membrane with a strong preference for water over oil is integrated into a droplet microfluidic system and observed to allow the passage of the transported aqueous phase droplets while blocking the continuous phase. The oil breakthrough pressure of the membrane was observed to be 250 ± 20 kPa, a much greater pressure than anywhere within the microfluidic channel, thereby eliminating the possibility that oil will leak from the microchannel, a critical parameter if droplet transport is to be used in needle-based drug delivery.

A parametric study on the application of microfluidics for emulsion characterization

This work focuses on the application of a microfluidics system that has capability to produce monodispersed oil-in-water (O/W) and water-in-oil (W/O) emulsions for emulsion formation and stability analysis. Deionized water, aqueous solutions of inorganic salts, and aqueous solutions of surfactants were used as the water phase. N-decane, n-hexadecane, and surfactant solutions of n-decane and n-hexadecane were used as the oil phase. Experimental results indicating the effects of organic phase, continuous and droplet phase flow rates, water-cut, oil%, salt and surfactant types and concentrations on droplet size are presented. Emulsion stability experiments were carried out by observing droplet coalescence and temporal evolution of the droplet size. NaCl, KCl and CaCl2 salts were used to study the effect of salt type and concentration on the droplet size during the formation of O/W and W/O emulsions. The type and concentration of the inorganic salts studied have a negligible effect on the droplet size of both O/W and W/O type emulsions. However, for a given set of external phase and droplet phase velocities, oil droplet size is observed to be considerably larger than the aqueous phase droplet size. Oil soluble (Span 80) and water soluble (Sodium dodecyl sulfate) surfactants caused a significant reduction in droplet sizes for both O/W and W/O emulsions. It was also observed that the formation of droplets does not necessarily guarantee the stability of emulsions as rapid droplet coalescence occurs in some cases, especially in the absence or at low surfactant concentrations.

3D printing of microfluidic devices with embedded sensing electrodes for generating and measuring the size of microdroplets based on contactless conductivity detection

This report describes the 3D printing of integrated microfluidic platforms containing microchannels and embedded sensing electrodes for capacitively coupled contactless conductivity detection (C4D). Sensing electrodes were printed on poly(lactic acid) filament doped with carbon nanotubes and then integrated with fluidic channels printed on acrylonitrile butadiene styrene. The proposed microfluidic chips were explored to generate and measure the size of microdroplets based on C4D measurements. To the best of our knowledge, this is the first report showing the entire fabrication of an integrated platform by 3D printing as well as its use for measuring the size of droplets. The proof-of-concept was successfully demonstrated by generating oil droplets in an aqueous phase and water droplets in an oil phase. The droplet sizes were estimated based on their residence time within the detection cell in association with the flow velocity. According to the data achieved by C4D measurements, the length of water droplets decreased from 3.4±0.1 to 2.3±0.1mm when the total flow rate raised from 15 to 55μLmin−1. For oil droplets, length values ranged from 3.6±0.1 to 2.4±0.1mm at the same flow rate range. The achieved results exhibited an exponential correlation with the data obtained by optical measurements.

Microcellular open porous polyester membranes from thiol-ene polymerisations of high internal phase emulsions

A high internal phase emulsion templating procedure is applied for the preparation of membranes which exhibit an open porous morphology with interconnected macro pores and open porous surfaces. A doctor blading procedure is used to cast the high internal phase emulsion onto glass substrates. Continuous phase of the emulsions contain divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) which are photopolymerised using the thiol-ene click chemistry to yield polyester type polymer network. The resulting polymer morphology features primary pores as a result of emulsion’s droplet phase, with diameters between 7 and 14 µm and interconnecting pores as a result of polymerisation shrinkage, with diameters between 1.6 and 2.2 µm. The highly porous and interconnected morphology mirrors the precursor emulsion structure with a dense packing of internal (aqueous) phase droplets. Doctor blades with different slit dimensions are used for casting thus producing membranes with different thicknesses while in all cases typical polyHIPE morphology is observed. Mechanical tests show a dependence of tensile modulus and tensile strength on the membrane thickness and also on pore size distribution.

Binder Design for Asphalt Mixes with Reduced Temperature: EVA Modified Bitumen and its Emulsions

High energy consumption and environmental risks are both associated to the use of hot asphalt mixes. In response to the need of more sustainable pavements, the modification of bitumen with low melting point EVA copolymers is investigated. Firstly, different modified binders containing EVA with varying VA contents (and so different crystalline fractions and melting temperatures) and Melt Flow Index (MFI) values were investigated. In the second stage, emulsification was implemented, in which the above EVA modified bitumen was suspended in the form of micro-size droplets in aqueous phase, in the presence of a surfactant. The results suggest that an optimum balance between VA content and MFI value will improve the binder rheological performance at medium-high in-service temperatures as well as its workability, and will facilitate its emulsification. Additionally, the binder viscosity is tremendously reduced after its emulsification, which allows mixing to be performed at much lower temperature, so reducing both energy consumption and environmental risks.

Gold Deposition at a Free-Standing Liquid/Liquid Interface: Evidence for the Formation of Au(I) by Microfocus X-ray Spectroscopy (μXRF and μXAFS) and Cyclic Voltammetry

Electrochemical gold nucleation and nanoparticle growth at a liquid/liquid interface were examined in situ by combined X-ray fluorescence (XRF) mapping with a microfocus X-ray beam and X-ray absorption fine structure (XAFS) spectroscopy. Gold deposition was achieved by reduction of [AuCl4]− with tri-p-tolylamine at a water/1,2-dichlorobenzene interface using a windowless liquid/liquid interface system formed from the contact of aqueous and organic phase droplets. The combination of XRF and XAFS, with a spatial resolution of approximately 70 μm, provided chemical speciation information near the interface under gold deposition conditions. Analysis of the X-ray absorption near-edge structure (XANES) reveals evidence for the presence of Au(I) species as a reduction intermediate, concomitant with a buildup of metallic gold at the interface. Cyclic voltammetry indicates the presence of two ion transfer peaks at the liquid/liquid interface, which are assigned to the transfer of [AuCl4]− and [AuCl2]−. Finally ex situ TEM analysis shows that the resultant nanoparticles have an average size between 3 and 4 nm. In line with this particle size, the XAFS indicates bulk-like structure.

Kinetic Factors in the Synthesis of Silver Nanoparticles by Reduction of Ag+ with Hydrazine in Reverse Micelles of Triton N-42

The growth kinetics of silver nanoparticles (AgNPs) during the reduction of AgNO3 by hydrazine in the droplets of dispersed aqueous phase encapsulated in the reverse micelles of oxyethylated surfactant Triton N-42 with decane as disperse medium was studied in situ by UV–vis spectroscopy. The mechanism of the process includes two steps that are slow, continuous nucleation and fast, autocatalytic surface growth. Both steps are under kinetic control and are limited by the rate of Ag+ reduction. The rate of nucleation is limited by reaction in the droplets of the aqueous phase forming the cores of reverse micelles, and the rate of the growth is limited by the reaction on the surface of AgNPs growing inside the micelles. The reduction of Ag+ is a second-order process with respect to N2H4. It includes the formation of the intermediate complex Ag(N2H4)+ and its reaction with another N2H4 molecule. The concentration effects of N2H4 (c′N2H4) and NH3 (c′NH3) as competing ligand, medium effects of ionic strength (I) and of the background salt in dispersed aqueous phase, the effect of solubilization capacity of the micellar solution (Vs/Vo), and the effect of temperature (T) on the observed rate constants for the steps were studied. An increase in c′N2H4, I, Vs/Vo and T can be used to accelerate the rates of both steps, whereas an increase in c′NH3 inhibits them. The background salts have a positive effect on the rate of nucleation, whereas their effect on the growth rate is small and has probably a negative trend. The size and composition of AgNPs were characterized by means of DLS, TEM, EDXA, XRD, UV–vis, and IR spectroscopy.

Carbon nanotubes in emulsion-templated porous polymers: Polymer nanoparticles, sulfonation, and conductivity

Sulfonated polymers are of interest for ion exchange resins, reaction supports, and membranes for separation, filtration, fuel cells, and electrochemical devices. Sulfonic groups have been introduced into polystyrene (PS) through exposure to sulfuric acid, and carbon nanotubes (CNTs) have been added to polymers to enhance proton conductivity without creating an electronic percolation pathway. PolyHIPEs, emulsion-templated porous polymers with highly interconnected hierarchical open-cell porous structures, are synthesized through polymerization in the external phases of high internal phase emulsions (HIPEs). In this article, the synthesis of PS-based CNT-filled polyHIPEs, their structure, sulfonation, and conductivity are described. Adding CNT dispersions to the HIPEs produced polymer nanoparticle–covered polyHIPEs from polymerization within the water-soluble surfactant micelles in the internal aqueous phase droplets. The CNTs migrated from the HIPE's aqueous phase droplets into the HIPE's organic phase and formed interconnected bundles within the polyHIPE walls, reflecting a reduction in the surfactant's ability to disperse the CNTs. The water adsorption in the hygroscopic sulfonated polyHIPEs increased the conductivity by several orders of magnitude. The conductivity of the sulfonated polyHIPE containing CNTs was more than an order of magnitude greater than that of the sulfonated polyHIPEs with no CNTs. The CNTs act as “bridges,” enhancing the connection between existing conductive pathways. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4369–4377

Ultrasound Assisted-Temperature Controlled Ionic Liquid Microextraction of Trace Copper and Silver after Chelation with Dithizone and Their Determination by Flame Atomic Absorption Spectrometry in Food and Water Samples

Hydrophobic ionic liquid can be dispersed into infinite droplets in aqueous phase with sonication at 50°C, and then they can aggregate as large droplets at low temperature. Based on this phenomenon a new liquid-phase microextraction for preconcentration of copper and silver ions was developed. These ions were chelated by dithizone and extracted into the ionic liquid phase. Important parameters affected the extraction efficiency including pH, amount of chelating agent, volume of ionic liquid, extraction time, centrifugation time and temperature have been investigated. The interference study showed that common ions in real samples had no obvious negative effect on the recovery of analytes. The proposed method had a good linearity in range of 10 - 100 ng mL−1 for both ions. For copper the precision at 20 ng mL−1 was 3.0% (RSD, n = 5) and the detection limit was 2 ng mL−1 and for silver the precision at 50 ng mL−1 was 2.9% (RSD, n = 5) and the detection limit was 1.2 ng mL−1. The method was applied to the analysis of food and water samples.

Microorganism viability influences internal phase droplet size changes during storage in water-in-oil emulsions

Water-in-oil emulsions provide an alternative for long-term stabilization of microorganisms. Maintaining physical stability of the emulsion and cell viability is critical for large-scale application. Water-in-oil (W/O) emulsions were prepared with the biolarvacide Lagenidium giganteum and the green alga Chlorella vulgaris. Physical stability was measured via light scattering measurements of the internal phase droplets and cell viability was measured by plating and enumerating colony forming units. Emulsions were demonstrated to stabilize L. giganteum and C. vulgaris for more than 4 months without refrigeration. Introducing nutrients into the internal phase of W/O emulsions without cells had no significant effect on changes in aqueous phase droplet size dynamics. Internal phase droplet size changes that occurred over time were greater in the presence of cells. Increases in droplet size were correlated with cell death indicating measurement of internal phase droplet size changes may be an approach for monitoring declines in cell viability during storage.