Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

A STUDY OF SILICONE OIL-IN-WATER EMULSIONS

Emulsions of silicone oil-in water were formed using a Brinkmann Polytron homogenizer with Igepal CO-530 as an emulsifier. Silicone viscosities ranged from 10 to 33,000 mPa.s at 25°C. Rheological characteristics and particle size analyses of silicone oil-in-water emulsions were studied. At high volume fraction of the dispersed phase (70%-75%), silicone oil-in-water emulsions were stable. At lower volume fractions (50%-60%), emulsions formed were less stable and the two phases easily separated in a few days. The emulsions formed with high volume fraction silicone oil show highly non-Newtonian behavior (shear thinning). Emulsions made with low viscosity oils had lower viscosities than those made from high viscosity oils. Relative viscosity-concentration data could be correlated by the Frankel and Acrivos Equation. Increasing the emulsifier concentration of 70% oil-in-water emulsions resulted in a decrease in mean droplet size and an increase in emulsion viscosity. Increasing the intensity of agitation also resulted in higher viscosity and smaller droplet size until a critical energy input above which droplet size increased. Emulsification with low shear mixing provides more control in decreasing mean droplet size with time.     

Spontaneous spreading of emulsions on solid surfaces: Morphology and dynamics

The spontaneous spreading of emulsions of water dispersed in silicone oil onto glass surfaces is examined using differential interference contrast (DIC) microscopy. Spreading occurs via a precursor film from which the emulsion droplets are excluded. The radius of the interline of the bulk drop is found to vary as (time)^1/10, as is commonly observed for the spontaneous spreading of pure liquids. The spreading rate constant decreases linearly with the volume percent of the dispersed phase, but drops suddenly to zero at approximately 73% dispersed phase. The width and spreading rate of the precursor film also is found to decrease with dispersed phase concentration. A fingering type of instability is evident at the leading edge of the precursor film, yet has little effect on the spreading rate of either the precursor film or the droplet interline. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1817–1825, 2001     

Intensification of production of O/W emulsions using oscillatory woven metal micro-screen (WMMS)

Using high porosity woven metal micro-screen (WMMS), a novel design oscillatory emulsifier had been used for intensification of production of relatively narrow size distribution oil in water (O/W) emulsions. The average droplet size increased with increasing the dispersed phase flow and decreased with increasing both the oscillation frequency and amplitude. The emulsion polydispersity decreased with increasing both oscillation intensities as well as dispersed phase flux. Although the change in droplet size with oscillation was reasonably predicted using a simple torque balance model based on Stokes oscillatory flow, both the flow patterns and the surface phenomena are more complex, and the final droplet size is affected by interactions between different operating and physical parameters.     

ABA low molar mass triblock copolymers in reverse emulsions: A rheological study

The effect of blocks length and molar mass of ABA triblock copolymers on the rheological behavior of water in oil (w/o) emulsions was investigated. Emulsion parameters such as water droplet concentration (and droplet size) of a series of inverted emulsion systems were evaluated. All copolymer/emulsion systems studied showed a non-Newtonian behavior, and the presence of the copolymer in the emulsion system led to an increase of the low shear viscosity when the size of the midblock of the copolymer was in a specific size range. This suggests the formation of a transient network through the interconnection, by the copolymer, of the smaller water droplets present in the emulsion. Consequently, the systems behave as w/o emulsions containing reversibly crosslinked oil-soluble polymers in the continuous phase, resulting in a pronounced shear thinning behavior. For the different emulsions studied, the relative viscosity increased, with few exceptions, with increasing droplet concentration. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Stabilization of liquid water-in-oil emulsions by modifying the interfacial interaction of glycerol monooleate with aqueous phase ingredients

Glycerol monooleate (GMO)-stabilized liquid water-in-vegetable oil emulsions are difficult to stabilize due to the desorption of GMO from the water-vegetable oil interface toward the oil phase. This work improved the stability of GMO-stabilized liquid 20 wt% water-in-canola oil (W/CO) emulsion by modifying the dispersed aqueous phase composition with hydrogen bond-forming agents. As a control, 20 wt% water-in-mineral oil (W/MO) emulsion was also utilized. Different concentrations of hydrogen bond-forming agents (citric acid (CA), ascorbic acid (AA), low methoxyl pectin (LMP)) with and without salts (sodium chloride (S) or calcium chloride (Ca)) were added to the aqueous phase before emulsification, which enhanced emulsifier binding to the water–oil interface. W/CO emulsion without any aqueous phase additive destabilized instantly, whereas W/MO emulsion stayed stable during the week-long observation. The addition of hydrogen bond-forming agents and salts significantly improved emulsion stability. LMP, with many hydrogen bond-forming groups, was able to provide the highest emulsion stability after 7 days in both oils compared to AA, CA and their mixtures with S. Emulsions with both oils formed weak gels due to the formation of an extensive network of water droplet aggregates. Overall, the hydrogen bond-forming agents interacted with GMO at the interface, thereby favoring their presence at the water droplet surface and significantly improving the stability of liquid W/CO emulsions. The knowledge developed in this research can be useful in utilizing GMO to stabilize liquid water-in-oil emulsions without using any fat crystal network.     

Physico-chemical properties of heavy crude oil-in-water emulsions stabilized by mixtures of ionic and non-ionic ethoxylated nonylphenol surfactants and medium chain alcohols

This work describes the formulation and evaluation of concentrated, heavy oil-in-water emulsions stabilized by mixtures of ethoxylated surfactants and normal alcohols. The rheology, stability and droplet size of these emulsions were investigated as functions of the emulsification process parameters. The parameters investigated for this study include emulsifier agent composition, presence of additives, pH and salinity of the continuous aqueous phase, emulsification temperature, oil content and emulsion aging. The produced emulsions had viscosities ranging from 30 to 150 mPa s and represent a 30-fold reduction of the crude oil viscosity. Sauter mean diameters of the droplets ranged from 10 to 50 μm. The emulsions were produced by mixing the oil with an aqueous solution containing medium normal-chain alcohols and small quantities of a mixture of ethoxylated nonylphenol and ethoxylated amine surfactants. The presence of these alcohols led to a sharp decrease in the droplet size of the emulsion. This size decrease had a direct impact on the emulsions’ stability and apparent viscosity. The rheological parameters of the aged emulsions were also essentially constant over a 42-day period.     

Gravity induced coalescence in emulsions with high volume fractions of dispersed phase in the presence of surfactants

We report studies on the effect of volume fraction and surfactant concentration on the kinetics of destabilization of emulsions under the influence of gravity. Model oil‐in‐water emulsions, designed to mimic crude oil–water emulsions, were prepared with varying volume fractions of dispersed oil but nearly identical normalized initial drop size distributions. The gravity separation process was observed by periodically withdrawing samples, and examining the droplet size distribution under the microscope. Experiments were performed for three volume fractions of dispersed phase and two surfactant concentrations (0.4 and 1.6% by weight). At higher oil fractions (20%) and a lower surfactant concentration (0.4%), it was observed that although the rate of coalescence increased, the actual oil separation was delayed. At higher surfactant concentrations (1.6%), the dominant factor in suppressing destabilization is the rate of drop to interface coalescence. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4379–4389, 2017     

Influence of oil phase concentration on droplet size distribution and stability of oil‐in‐water emulsions

The objective of this study was to investigate the effect of oil phase concentration, at different emulsification conditions concerning homogenization time and emulsifier content, on droplet size distribution and stability of corn oil‐in‐water emulsions. Emulsions were prepared with 3, 5, 10, and 20% w/w triethanolamine oleate (calculated on oil amount), 0.53% w/w carboxymethylcellulose (calculated on water amount), and 5, 10, 20, 30, or 40% w/w oil, and homogenized 5, 10, 20, and 60 min. It was found that increase in oil phase concentration led to decrease in specific surface area and increase in polydispersity of emulsion at lower emulsifier concentration and less intense homogenization. At emulsifier concentrations ≤10% and homogenization time ranges of 20–60 min the non‐monotonous variation in droplet size parameters with oil concentration was observed, as a result of the interaction between triethanolamine oleate and carboxymethylcellulose, which were confirmed by viscosity measurements. However, at emulsifier concentration of 20% an increase in specific surface area and decrease in polydispersity with the increase in oil concentration occurred due to an increase in equilibrium concentration of emulsifier in the continuous phase. Further, influence of oil concentration on emulsion creaming stability was found to be independent on emulsifier concentration and homogenization time. Therefore, a decrease in creaming with increase in oil concentration was observed in all the examined triethanolamine oleate (TEAO) concentration and homogenization time ranges. Practical applications: Emulsions are colloidal systems which can be encountered in different industrial sectors, such as food, pharmaceutical, cosmetics, oil industry, etc. Determination of the droplet size of emulsion is probably the most important way of their characterization, since it influences the properties of emulsion such as rheology, texture, shelf life stability, appearance, taste, etc. The size of the droplets depends on a wide range of parameters. One of them is certainly the concentration of the oil phase. However, since the impact of one parameter is often influenced with the intensity of the other variable involved in the emulsion generation, the aim of the present work was to examine the effect of corn oil concentration on droplet size parameters and stability of oil‐in‐water emulsions at different emulsification conditions. Therefore a step toward creation of emulsions with desired final properties was made.     

Effects of droplet size on the oxidative stability of oil-in-water emulsions

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806±0.0690, 3.28±0.0660, or 10.7±0.106 μm (mean ± SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 μm were significantly lower than those in the emulsion with a mean droplet size of 12.8 μm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 μm were lower compared with those of the emulsion with a mean droplet size of 12.8 μm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by ¹H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.     

Mass transfer coefficients of styrene and oxygen into silicone oil emulsions in a bubble reactor

The absorption of oxygen and styrene in water-silicone oil emulsions was independently studied in laboratory-scale bubble reactors at a constant gas flow rate for the whole range of emulsion compositions (0-10% v/v). The volumetric mass transfer coefficients to the emulsions were experimentally measured using a dynamic absorption method. It was assumed that the gas phase contacts preferentially the water phase. In the case of oxygen absorption, it was found that the addition of silicone oil hinders oxygen mass transfer compared to an air-water system. Decreases in k_La_oxygen of up to 25% were noted. Such decreases in the oxygen mass transfer coefficient, which imply longer aeration times to transfer oxygen, could represent a limiting step in biotechnological processes strongly dependent on oxygen concentration. Nevertheless, as the large affinity of silicone oil for oxygen enables greater amounts of oxygen to be transferred from the gas phase, it appears that the addition of more than 5% silicone oil should be beneficial to increase the oxygen transfer rate. In the case of styrene absorption, it was established that the volumetric mass transfer coefficient based on the emulsion volume is roughly constant with the increase in the emulsion composition. In spite of the relatively high cost of silicone oil, water-silicone oil emulsions remain relevant to treat low-solubility volatile organic compounds, such as styrene, in low-concentration gas streams.     

Emulgieren mit mikrostrukturierten Systemen

Emulsification using Microstructured Systems In the last century, research on several methods for the production of emulsions has been carried out. In order to disperse one phase into another phase which is immiscible or poorly miscible in the first phase, several kinds of processes are available. An example for emulsions where small oil droplets are dispersed into a continuous water phase is mayonnaise. In margarine, water droplets are dispersed into a continuous oil phase. In this publication, three emulsification methods are presented. First of all membrane emulsification was developed by Nakashima in the early 1990ies. This process uses microporous membranes to disperse one phase into another one. The disperse phase is pressed through the pores and detached by the flow of the continuous phase. This results in the production of an emulsion with a narrow droplet size distribution at mild process conditions. Another process using membranes for the production of emulsions is premix membrane emulsification, developed by Suzuki in the late 1990ies. Droplets of a coarse emulsion are disrupted by passing the entire emulsion through the pores of a membrane. Compared to the aforementioned method, higher production rates are possible. Nakajimaapplied the so called microchannels in emulsification technology. Compared to other emulsification methods, these three processes provide several advantages.     

Emulsifying and self‐emulsified properties of siloxane polymer grafted with easy hydrophile

A series of siloxane polymers (SHE) with varying weight percents of simple nonionic hydrophilic groups have been synthesized and characterized by FTIR and ¹³C‐NMR. Emulsions have been made by self‐emulsification of those polymers in pure water and also by emulsifying silicone oil using those polymers as oil‐in‐water type emulsifiers. The stability of those emulsions have been examined apparently from the phase separation and also from the particle size increase on storage by Transmission Electron Microscopy (TEM) and photo microscopy. The results reviled that SHE 40, having 40 wt % grafted hydrophile, formed the most stable self‐emulsified emulsion, and SHE30 and SHE40 could be used as effective emulsifiers for silicone oil emulsification. The possible use of those emulsions as a defoamer for water‐borne systems has also been investigated by measuring the reduction of foam height of a strongly foamed aqueous solution of sodium lauryl sulfate (SLS). The defoaming ability decreases with the increase in hydrophile wt % in the polymer backbone; however, it increases with the emulsion (defoamer) concentrations. When compared with respect to the total wt % of hydrophobe contents in the emulsion defomer, the self‐emulsified emulsion has shown better defoaming than the silicone oil emulsion, and the results are well in accord with the difference in size of the respective emulsion particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2408–2415, 2002     

Development of Nanoemulsion of Silicone Oil and Pine Oil Using Binary Surfactant System for Textile Finishing

Nanoemulsions of silicone oil and pine oil using a binary surfactant system were prepared. Silicone oil and pine oil were used to achieve softness and mosquito repellency and antibacterial activity respectively when the nanoemulsion was applied on the fabric. A silicone surfactant (AG-pt) and a hydrocarbon surfactant (TDA-6) were used in different proportions to obtain stable nanoemulsions at the lowest possible droplet size. The various emulsification process variables such as ratio of hydrocarbon to silicone surfactant, surfactant concentration, ratio of silicone oil to pine oil, oil weight fraction and sonication time have been studied. The optimal variables include the ratio of hydrocarbon to silicone surfactant of 80:20, surfactant concentration of 8%, ratio of silicone oil to pine oil of 80:20, oil weight fraction of 20% and 15 min of sonication time at 40% of the applied power. Nanoemulsions were found to be very stable with emulsion droplet size around 41 nm. In order to compare different emulsification techniques, emulsions were also prepared using the conventional method. Emulsions analyzed using SEM showed spherical droplets ranging from 40 to 120 nm. Atomic force microscopy was used to evaluate the bounciness, fluffiness and softness of fabric. From this study, it was found that stable nanoemulsion with a lowest possible droplet size of silicone and pine oil could be prepared by ultrasonic emulsification technique in order to deliver multiple properties when applied to fabric.     

Efficient Encapsulation of a Water-Soluble Molecule into Lipid Vesicles Using W/O/W Multiple Emulsions via Solvent Evaporation

We developed a novel method for preparing lipid vesicles with high entrapment efficiency and controlled size using water‐in‐oil‐in‐water (W/O/W) multiple emulsions as vesicle templates. Preparation consists of three steps. First, a water‐in‐oil (W/O) emulsion containing to‐be‐entrapped hydrophilic molecules in the water phase and vesicle‐forming lipids in the oil phase was formulated by sonication. Second, this W/O emulsion was introduced into a microchannel emulsification device to prepare a W/O/W multiple emulsion. In this step, sodium caseinate was used as the external emulsifier. Finally, organic solvent in the oil phase was removed by simple evaporation under ambient conditions to afford lipid vesicles. The diameter of the prepared vesicles reflected the water droplet size of the primary W/O emulsions, indicating that vesicle size could be controlled by the primary W/O emulsification process. Furthermore, high entrapment yields for hydrophilic molecules (exceeding 80 % for calcein) were obtained. The resulting vesicles had a multilamellar vesicular structure, as confirmed by transmission electron microscopy.     

Rotor‐Stator and Disc Systems for Emulsification Processes

Emulsions now find a wide range of applications in industry and daily life. In the pharmaceutical industry lipophilic active ingredients as well as many nutritional products such as vitamins are often formulated in the dispersed phase of oil‐in‐water emulsions. Emulsions can be produced with different mechanical emulsification techniques. In the following review, the process of rotor‐stator systems and disc systems are compared to other popular mechanical emulsification systems. On the basis of experimental results from the authors' laboratory, a discontinuous gear‐rim dispersing system, discontinuous disc system, and a continuous high pressure system are compared with regard to their attainable mean droplet diameter and drop size distribution in an oil‐in‐water emulsion. It can be shown that dissolver discs with a very simple geometry attain very small mean droplet diameters and a very narrow droplet size distribution, comparable to the emulsions obtained with established rotor‐stator systems such as gear‐rim dispersers.     

稠油包水乳状液的表观黏度

以渤海SZ36-1稠油、矿化水为工质配制了2组不同液滴直径的W/O型乳状液,研究了温度、含水率、剪切率和液滴直径对乳状液黏度的影响。结果表明,温度对乳状液表观黏度的影响非常明显,而对相对黏度的影响却较小;同时含水率、剪切率和液滴直径也是影响乳状液黏度的重要因素,低含水率下,剪切率、液滴直径对黏度的影响不明显,而当含水率较高时,剪切率、液滴直径的影响非常突出,乳状液呈现出强烈的剪切稀释特性。利用国内外现有的一些黏度模型对实验获得的黏度数据进行了预测分析,发现Brinkman(1952)模型具有较好的预测精度。     

Bubble/droplet formation and mass transfer during gas–liquid–liquid segmented flow with soluble gas in a microchannel

Microchannels have great potential in intensification of gas–liquid–liquid reactions involving reacting gases, such as hydrogenation. This work uses CO₂–octane–water system to model the hydrodynamics and mass transfer of such systems in a microchannel with double T‐junctions. Segmented flows are generated with three inlet sequences and the size laws of dispersed phases are obtained. Three generation mechanisms of dispersed gas bubbles/water droplets are identified: squeezing by the oil phase, cutting by the droplet/bubble, cutting by the water–oil/gas–oil interface. Based on the gas dissolution rate, the mass transfer coefficients are calculated. It is found that water droplet can significantly enhance the transfer of CO₂ into the oil phase initially. When bubble‐droplet cluster are formed downstream the microchannel, droplet will retard the mass transfer. Other characteristics such as phase hold‐up, bubble velocity and bubble dissolution rate are also discussed. The information is beneficial for microreactor design when applying three‐phase reactions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1727–1739, 2017     

玉米油W1/O/W2型多重乳状液稳定性的研究

高脂食品严重危害着人类健康,这引起人们对低脂食品的的不断追求,因此脂肪替代品的开发越来越受到人们重视。本试验以玉米油和生物高聚物为主要原料通过两步乳化法制备W1/O/W2多重乳状液作为脂肪替代品(FS),以离心稳定性为衡量标准,用显微镜直接观察,探讨了初复乳乳化工艺、各相相对体积比对玉米油W1/O/W2型多重乳状液体系稳定性的影响。结果表明:1.影响玉米油多重乳状液稳定性的主要因素有:复乳的乳化工艺,内水相与油相体积之比等。2.两步乳化工艺中第二步乳化工艺对复乳稳定性影响较大,其规律是随着乳化强度的提高,粒径减小,稳定性呈上升趋势,适宜的乳化条件为7200 r.min.1,13 min,而第一步乳化工艺对复乳稳定性几乎没有影响。3.内水相与油相、初乳与外水相均是影响复乳稳定性的主要因素,前者主要是依靠改变初乳黏度来影响复乳稳定性,后者主要是乳滴间范德华力与电排斥力共同作用的结果,适宜的体积比分别为1:4和1:1。