Monodisperse w/w/w Double Emulsion Induced by Phase Separation

We develop an approach to fabricate monodisperse water-in-water-in-water (w/w/w) double emulsion in microfluidic devices. A jet of aqueous solution containing two incompatible solutes, dextran and polyethylene glycol (PEG), is periodically perturbed into water-in-water (w/w) droplets. By extracting water out of the w/w droplet, the solute concentrations in the droplet phase increase; when the concentrations exceed the miscibility limit, the droplet phase separates into two immiscible phases. Consequently, PEG-rich droplets are formed within the single emulsion templates. These PEG-rich droplets subsequently coalesce with each other, resulting in transiently stable w/w/w double emulsions with a high degree of size uniformity. These double emulsions are free of organic solvents and thus are ideal for use as droplet-vessels in protein purification, as microreactors for biochemical reactions, and as templates for fabrication of biomaterials.     

Water in oil (w/o) and double (w/o/w) emulsions prepared with spans: microstructure,stability, and rheology

The objective was to analyze the microstructure, stability, and rheology of model emulsions prepared with distilled water, refined sunflower oil, and different Spans (20, 40, 60, and 80) as emulsifiers. The effects of the water content and Span 60 concentration were studied. The lowest water contents led to w/o emulsions, whereas higher percentages gave w/o/w emulsions. Microscopy analysis showed that w/o/w emulsions of higher water contents had a lower number of internal water droplets. W/o emulsions were destabilized by coalescence and sedimentation, whereas creaming was observed in unstable w/o/w emulsions. In the last ones, the creaming stability decreased with increasing water content and enhanced with higher Span 60 concentration; the same effect was observed in their viscoelasticity: They were from unstable liquids to stable gels. Solid Spans (40 and 60) produced more consistent w/o/w emulsions at low water contents and more stable systems at high water percentages in comparison with liquid Spans (20 and 80).     

Preparation of metal nanoparticles in water-in-oil (w/o) microemulsions

The use of an inorganic phase in water-in-oil microemulsions has received considerable attention for preparing metal particles. This is a new technique, which allows preparation of ultrafine metal particles within the size range 5 nm相似文献   

Characterization of Interfacially Active Fractions and Their Relations to Water-in-Oil Emulsion Stability.

Natural surfactants from four crude oils have been extracted by adsorption on silica after precipitation of the asphaltenes by means of centrifugation or decantation. The extracted fractions have been characterized, analytically by FT-IR spectroscopy (chemical functions) and chromatography (molecular weight and polarity) and by their interfacial properties with emulsification and interfacial tension measurements on the model system water/decane with interfacially active fractions in different concentrations. The importance of these fractions (precipitated and adsorbed) on the stability of w/o emulsions is investigated. The influence of some extraction parameters (centrifugation or decantation, different adsorbents) on the nature and the emulsion behaviour of the fractions is studied and shows that the classification of the surfactants (asphaltenes, resins) is diffuse. It also shows that all the interfacially active constituents of the crude are interacting and are involved in the interfacial processes.     

部分析因法分析油包水型聚乙烯亚胺水溶液/石蜡乳液的稳定性

聚乙烯亚胺(PEI)及其乳状液被广泛用于酶固定化、基因治疗、污水处理等领域。 为提高PEI乳状液的稳定性,促进其应用,本文采用部分析因试验法考察了影响PEI水溶液/石蜡乳状液(W/O)稳定性的主因素和各因素间交互作用。 结果表明,乳化剂用量和PEI的水相质量分数是影响PEI水溶液/石蜡乳液稳定性的主因素。 PEI的水相质量分数和油/水体积比的交互作用最显著。 优化后,制备最稳定的PEI水溶液/石蜡乳状液(W/O)的条件是:m(Span-80):m(Tween-80)=6:1,PEI的水相质量分数为5%,乳化剂用量为0.07 g/mL,V(石蜡):V(PEI水溶液)=6:4,均质时间为3 min,转速为6000 r/min。 在优化条件下制备的PEI水溶液/石蜡乳状液在放置7 d后乳状液的外观无明显变化,这表明所制备的PEI水溶液/石蜡乳状液具有良好的稳定性。     

Lipophilicity assessment of basic drugs (log P(o/w) determination) by a chromatographic method

A previously reported chromatographic method to determine the 1-octanol/water partition coefficient (log P(o/w)) of organic compounds is used to estimate the hydrophobicity of bases, mainly commercial drugs with diverse chemical nature and pK(a) values higher than 9. For that reason, mobile phases buffered at high pH to avoid the ionization of the solutes and three different columns (Phenomenex Gemini NX, Waters XTerra RP-18 and Waters XTerra MS C(18)) with appropriate alkaline-resistant stationary phases have been used. Non-ionizable substances studied in previous works were also included in the set of compounds to evaluate the consistency of the method. The results showed that all the columns provide good estimations of the log P(o/w) for most of the compounds included in this study. The Gemini NX column has been selected to calculate log P(o/w) values of the set of studied drugs, and really good correlations between the determined log P(o/w) values and those considered as reference were obtained, proving the ability of the procedure for the lipophilicity assessment of bioactive compounds with very different structures and functionalities.     

Study and modeling of iron hydroxide nanoparticle uptake by AOT (w/o) microemulsions

Control over nanoparticle size is a key factor which labels a given preparation technique successful. When organic reactions are mediated by ultradispersed catalysts, the concentration of the colloidal nanoparticle catalysts and their stability become key factors as well. In this study, variables affecting iron hydroxide nanoparticle size, stability, and maximum possible colloidal concentration in AOT/water/isooctane microemulsions were investigated. Iron hydroxide was prepared in single microemulsions by first solubilizing iron chloride powder in the water pools, followed by addition of aqueous NaOH. Upon addition of NaOH, Fe(OH)3 nanoparticles stabilized in the water pools formed in addition to bulk precipitate of Fe(OH)3. The time-invariant concentration of the stabilized Fe(OH)3 is defined as the nanoparticle uptake, and it corresponds to the maximum possible concentration of the colloidal nanoparticles. The effect of the following variables on the nanoparticle uptake and size distribution was investigated: mixing time; surfactant concentration; water to surfactant mole ratio; and the initial concentration of the precursor salt. At 300 rpm of mixing a constant uptake of iron hydroxide nanoparticles was achieved in about 2 h and further mixing had limited effect on the nanoparticle uptake and particle size. An optimum R was found for which a maximum nanoparticle uptake was obtained. Nanoparticle uptake increased linearly with the surfactant concentration and displayed a power function with the initial concentrations of the precursor salt. The surface area/g of the nanoparticles was much higher than literature values, however, following a trend opposite to that of the nanoparticle uptake. The surface area/unit volume of the microemulsion, on the other hand, followed the same trend as the nanoparticle uptake. The particle size increased as R and/or the surfactant concentration increased. A mathematical model based on correlations for water uptake by Winsor type II microemulsions accurately accounted for the effect of the aforementioned variables on the nanoparticle uptake.     

Metal-ion retention properties of water-soluble amphiphilic block copolymer in double emulsion systems (w/o/w) stabilized by non-ionic surfactants

Metal-ion retention properties of water-soluble amphiphilic polymers in presence of double emulsion were studied by diafiltration. Double emulsion systems, water-in-oil-in-water, with a pH gradient between external and internal aqueous phases were prepared. A poly(styrene-co-maleic anhydride) (PSAM) solution at pH 6.0 was added to the external aqueous phase of double emulsion and by application of pressure a divalent metal-ion stream was continuously added. Metal-ions used were Cu(2+) and Cd(2+) at the same pH of polymer solution. According to our results, metal-ion retention is mainly the result of polymer-metal interaction. Interaction between PSMA and reverse emulsion globules is strongly controlled by amount of metal-ions added in the external aqueous phase. In addition, as metal-ion concentration was increased, a negative effect on polymer retention capacity and promotion of flocculation phenomena were produced.     

One-step formation of w/o/w multiple emulsions stabilized by single amphiphilic block copolymers

Multiple emulsions are complex polydispersed systems in which both oil-in-water (O/W) and water-in-oil (W/O) emulsion exists simultaneously. They are often prepared accroding to a two-step process and commonly stabilized using a combination of hydrophilic and hydrophobic surfactants. Recently, some reports have shown that multiple emulsions can also be produced through one-step method with simultaneous occurrence of catastrophic and transitional phase inversions. However, these reported multiple emulsions need surfactant blends and are usually described as transitory or temporary systems. Herein, we report a one-step phase inversion process to produce water-in-oil-in-water (W/O/W) multiple emulsions stabilized solely by a synthetic diblock copolymer. Unlike the use of small molecule surfactant combinations, block copolymer stabilized multiple emulsions are remarkably stable and show the ability to separately encapsulate both polar and nonpolar cargos. The importance of the conformation of the copolymer surfactant at the interfaces with regards to the stability of the multiple emulsions using the one-step method is discussed.     

Study and Modeling of Metal Oxide Solubilization in (w/o) Microemulsions

Water-in-oil (w/o) microemulsions are very appealing reaction media due to their ability to provide huge surface of contact between water-soluble and oil-soluble reactants. Their application as reaction media, including the preparation of nanoparticles, is, however, limited to water soluble precursors. In this study, we present a first step scheme in a two-step process for the preparation of metal oxide nanoparticles starting from their water-insoluble metal oxide bulk powder. This step involves solubilizing the metal oxide in the water pools of the microemulsion with the aid of a solubilizing agent. The variables affecting the solubilizing capacity of iron and copper oxides, as examples of important metal oxides, in single HCl-containing AOT/water/isooctane microemulsions were investigated. The effect of the following variables on the solubilization capacity is reported, namely, mixing time, surfactant concentration, water to surfactant mole ratio (R), and the nominal concentration of HCl in the water pool. At 300-rpm, time-invariant concentration of the metals in the microemulsions was achieved in about 6 hours. These values were quoted as the solubilization capacity of the metal oxide at the corresponding conditions. Solubilization capacity increased linearly with the surfactant concentration and R, and portrait a power function with the nominal concentration of HCl in the water pool. A mathematical model previously derived to describe nanoparticle uptake by single microemulsion accurately accounted for the effect of the aforementioned variables on the solubilization capacity.     

Degradation of kinetically-stable o/w emulsions

This article summarizes the studies on the degradation of the thermodynamically unstable o/w (nano)emulsion--a dispersion of one liquid in another, where each liquid is immiscible, or poorly miscible in the other. Emulsions are unstable exhibiting flocculation, coalescence, creaming and degradation. The physical degradation of emulsions is due to the spontaneous trend toward a minimal interfacial area between the dispersed phase and the dispersion medium. Minimizing the interfacial area is mainly achieved by two mechanisms: first coagulation possibly followed by coalescence and second by Ostwald ripening. Coalescence is often considered as the most important destabilization mechanism leading to coursing of dispersions and can be prevented by a careful choice of stabilizers. The molecular diffusion of solubilizate (Ostwald ripening), however, will continuously occur as soon as curved interfaces are present. Mass transfers in emulsion may be driven not only by differences in droplet curvatures, but also by differences in their compositions. This is observed when two or more chemically different oils are emulsified separately and the resulting emulsions are mixed. Compositional ripening involves the exchange of oil molecules between emulsion droplets with different compositions. The stability of the electrostatically- and sterically-stabilized dispersions can be controlled by the charge of the electrical double layer and the thickness of the droplet surface layer formed by non-ionic emulsifier. In spite of the similarities between electrostatically- and sterically-stabilized emulsions, there are large differences in the partitioning of molecules of ionic and non-ionic emulsifiers between the oil and water phases and the thickness of the interfacial layers at the droplet surface. The thin interfacial layer (the electrical double layer) at the surface of electrostatically stabilized droplets does not create any steric barrier for mass transfer. This may not be true for the thick interfacial layer formed by non-ionic emulsifier. The interactive sterically-stabilized oil droplets, however, can favor the transfer of materials within the intermediate agglomerates. The stability of electrosterically-stabilized emulsion is controlled by the ratio of the thickness of the non-ionic emulsifier adsorption layer (delta) to the thickness of the electrical double layer (kappa(-1)) around the oil droplets (delta/(kappa(-1))) = (deltakappa). The monomer droplet degradation can be somewhat depressed by transformation of coarse emulsions to nano-emulsion (miniemulsion) by intensive homogenization and by the addition of a surface active agent (coemulsifier) or/and a water-insoluble compound (hydrophobe). The addition of hydrophobe (hexadecane) to the dispersed phase significantly retards the rate of ripening. A long chain alcohol (coemulsifier) resulted in a marked improvement in stability, as well, which was attributed to a specific interaction between alcohol and emulsifier and to the alcohols tendency to concentrate at the o/w interface to form stronger interfacial film. The rate of ripening, according to the Lifshitz-Slyozov-Wagner (LSW) model, is directly proportional to the solubility of the dispersed phase in the dispersion medium. The increased polarity of the dispersed phase (oil) decreases the stability of the emulsion. The molar volume of solubilizate is a further parameter, which influences the stability of emulsion or the transfer of materials through the aqueous phase. The interparticle interaction is expected to favor the transfer of solubilizate located at the interfacial layer. The kinetics of solubilization of non-polar oils by ionic micelles is strongly related to the aqueous solubility of the oil phase (the diffusion approach), whilst their solubilization into non-ionic micelles can be contributed by interparticle collisions.     

Carbon nanotube capsules self-assembled by w/o emulsion technique

Carbon nanotube capsules (CNCs) with the diameter of 5-10 microm were fabricated from acid-modified multiwalled carbon nanotubes (CNTs) using water-in-oil (W/O) emulsion technique. The effects of the content of CNTs in water, the extent of acid treatment, and the length of CNTs used on the formation and morphology of CNCs were investigated. It was found that the amount of CNTs in water and the length of CNTs are the crucial factors for the formation of carbon nanotube capsules.     

离心-电导联用法快速评价O/W乳状液稳定性

建立了乳状液在重力场和离心力场中的沉降/分层速率模型,利用离心加速乳状液的沉降/分层,根据分层后富水相的电导随离心时间的变化关系得到乳状液在离心场中的稳定时间tc,进而推算出乳状液在重力场中的稳定时间tg。这种离心-电导联用方法可快速评价O/W乳状液的稳定性。例如,以质量分数为4%Pluronic F68、1.2%卵磷脂、8%甘露醇和10%IPM配置的乳状液,在8000r/min离心下测得tc为22min,计算出tg为69d;定性分析得到离心分层常数KA=48.0%,结果表明,该配方可得到稳定的O/W乳状液。     

Thermal Behaviour of Perfluoropolyether w/o Percolative Microemulsions

The thermal properties of a perfluoropolyether (PFPE) W/O microemulsion were investigated by Differential Scanning Calorimetry (DSC) both on freezing the liquid samples and upon their melting. PFPE systems as a function of increasing volume fraction (Φ=water+surfactant/total), were studied along a dilution line with a water/surfactant molar ratio W/S=11. The percolative nature of these systems emerged directly from the spreading of the exothermic peaks associated with the freezing of the dispersed phase. This behaviour was found to depend on whether the starting temperature of the DSC measure was at, below or above the percolative threshold temperature of the given sample. A low temperature 'needle-like' peak was found around 143 K, immediately after the glass transition due to the oil continuous phase. The low temperature peak was also present in other percolative, three-component microemulsions. The higher order phase transition at the percolation temperature was also evidenced. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and Evaluation of New Demulsifiers Incorporating Linear Alkyl Benzene Moiety for Treating Water-in-Oil Emulsion

In the present study, five types of water soluble demulsifiers based on linear alkyl benzene were prepared. The chemical structures of the prepared demulsifiers were elucidated using Fourier transform-infrared (FTIR) and ¹H NMR spectra. Different factors affecting demulsification efficiency such as; water content, demulsifier concentration, hydrophilic lipophilic balance (HLB), and ethylene oxide unit were investigated. Also, the rheological properties in relation to demulsification efficiency were studied. The surface and thermodynamic parameters of the prepared demulsifiers were determined at 25°C including, surface tension (γ) and effectiveness, maximum surface excess (Γ_max), and minimum surface area (A_min). From the obtained data, it was found that the demulsification efficiency increases with increasing the water content and concentration of the demulsifiers. Primarily evaluation study of demulsification performance of the new demulsifiers showed that as the ethylene oxide unit in the demulsifiers increase (10–40 ethylene oxide units), the performance of the demulsifiers increasing, however, it decrease in case of demulsifiers with (80 ethylene oxide unit).     

Cross-linked starch nanoparticles stabilized Pickering emulsion polymerization of styrene in w/o/w system

Here, we present a method to synthesize expandable spherical polystyrene beads containing well-dispersed water microdroplets. The beads, 2–3 mm in diameter, were prepared through surfactant-free Pickering emulsion polymerization in water-in-oil-in-water (w/o/w) system using cross-linked starch nanoparticles (CSTN) as emulsifier. The CSTNs were in situ surface-modified by styrene maleic anhydride copolymer as confirmed by infrared spectroscopy and contact angle analysis. The entrapped water microdroplets with the average size of 3–4 μm were shown to be surrounded by a dense layer of the CSTN. The number droplet density as well as water encapsulation efficiency in the polystyrene beads increased with the CSTN concentration. Furthermore, regardless of CSTN content, all samples exhibited high encapsulation stability of over 68 % after 3 months. These characteristics along with good expansion behavior suggest the synthesized beads as expandable polystyrene containing water as a green blowing agent.     

Mechanism of Electrical Percolation of w/o Microemulsions Formed by Nonionic Surfactants

A study was carried out on the mechanism of electrical conductivity percolation of H₂O/C₁₆EO₂₀/n-butanol/heptane microemulsions. Electrical conductivity, UV-vis spectroscopy and FTIR spectra were used to study the diluted “dry” microemulsions with the mass ratio of C₁₆EO₂₀/n-butanol/heptane = 3:3:4. The results of electrical conductivity showed that the percolation occurred around φ_w = 20 wt% and the transition of w/o microemulsions to bicontinueous microemulsions happened when φ_w = 45 wt%. From the UV-vis absorption spectra, it was found that the absorption of methyl orange (MO) in microemulsions shifted red than that of in oil phase, but the maximal absorption peak (λ_max) remained unchanged when φ_w > 20 wt%. It implied that the position of MO solubilized in microemulsions was unvaried after free water appeared in the core. FTIR spectra revealed that the OH band of water in microemulsions moved to high frequency at low φ_w (< 20 wt%) and became broader at high φ_w. It indicated that the added water only caused the hydration of EO at low φ_w, the hydration completed when φ_w > 20 wt% and then the residual water entered into the core with properties similar to bulk water. The presence of free water as ions exchange medium will cause the electrical conductance increased. The percolation appeared after the hydration of EO completed.     

Fabrication of polymersomes with controllable morphologies through dewetting w/o/w double emulsion droplets

In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The dewetting process can be tuned by solvation between solvent and amphiphilic block copolymer to get polymersomes with controllable morphology. Good solvent(chloroform and toluene) hinders dewetting process of double emulsion droplets and gets acornlike polymersomes or patched polymersomes. On the other hand, poor solvent(hexane) accelerates the dewetting process and achieves complete separation of inner water phase from oil phase to form complete bilayer polymersomes. In addition, twin polymersomes with bilayer membrane structure are formed by this facile method. The formation mechanism for different polymersomes is discussed in detail.     

Action of emulsifiers during homogenization of o/w emulsions

Droplet size and size distribution changes at homogenization of paraffin oil emulsions, stabilized by different concentrations of various emulsifiers, were investigated. During homogenization, samples were taken from emulsions and the most frequently occuring diameter, mean droplet diameter and standard deviation (distribution width) were determined. Mathematical relations describing changes of mean diameter and distribution width, as a function of the homogenization period and emulsifier concentration, were derived and applied to the experimental data. Emulsifier efficiencies and capabilities were characterized by physical constants and graphically. Optimal homogenization time interval, optimal emulsifier concentrations and corresponding droplet size distribution parameters were computed.