Coalescence Behavior of Pure and Natural Fat Droplets Characterized via Micromanipulation

For two approaching oil droplets, a region of arrested coalescence lies between full coalescence and total stability. Here the fusion of two droplets begins, but they are stopped from fully relaxing into one spherical droplet. The internal rigidity of the solid fat network within each droplet can provide the resistance necessary to arrest the shape change driven by Laplace pressure. These intermediate doublet structures lead to the partially‐coalesced fat networks important for the desired physical properties of ice cream and whipped topping. The use of micromanipulation techniques allows coalescence events between two oil droplets to be microscopically observed. In this study, oil droplets composed of different fats were manipulated at varying elastic moduli, interfacial tension, and radii. It was seen that increasing the elastic moduli of the droplets or increasing droplet radii resulted in coalescence being arrested earlier. Under these experimental conditions, different interfacial tensions did not change the coalescence behavior between two oil droplets.     

Water-in-triglyceride oil emulsions. Effect of fat crystals on stability

The influence of low concentrations (0.1-5%) of fat crystals on the stability of water-in-soybean oil emulsions was examined by light scattering and sedimentation experiments. Both the initial flocculation/coalescence rate and long-term stability against water separation were determined. The initial flocculation/coalescence rate increased upon addition of small amounts of fat crystals. When the crystal concentration was increased above a critical concentration (specific to a system), a decrease in the flocculation/coalescence rate occurred. The increased flocculation/coalescence rate is likely the effect of bridging of water droplets by fat crystals. Fat crystal wetting by water is an important criterion for this phenomenon to occur. Emulsion stabilization for crystal concentrations above critical is caused by a mechanical screening of water droplets. The presence of considerable amounts of crystals in oil also lowered the density difference between droplet and medium, and enhanced viscosity. The degree of increase in viscosity depended upon the emulsifier. Both a decrease in density difference and an increase in viscosity play a role in hindering flocculation/coalescence of droplets. In long-term studies of water separation, all concentrations of fat crystals stabilized the water-in-oil emulsions. The droplet size of these emulsions increased until the critical droplet size was approached where the screening effect of crystals on the droplets no longer stabilized the emulsions. The stabilizing effect for emulsions with monoolein was continuously improved by increasing the amount of crystals up to 5%. For lecithin-stabilized emulsions, an optimal effect was achieved for fact crystal concentrations of 1–2%.     

Interactions between fat crystal networks and sodium caseinate at the sunflower oil-water interface

A Couette-type torsion wire surface shear viscometer was used to measure the apparent interfacial shear viscosity of pH 7 (I=0.05 M) buffered solutions of sodium caseinate in contact with sunflower oil. The sunflower oil contained 1% fat crystals in either the β or β′ polymorphic form, or was crystal free. In all cases, the fat crystals increased the interfacial shear viscosity synergistically, with the β′ crystals causing the biggest increase. Substituting the protein for a small-molecule surfactant (Tween-40) showed that this was not simply due to the protein lowering the interfacial tension. Sedimentation studies of the different fat crystal slurries suggested that the extent of the interfacial shear viscosity increase was related to the strength of crystal-crystal interactions in the oil phase. It seems likely that when protein is present at the interface, it fixes the adsorbed layer of fat crystals to the cross-linked protein film at the interface. When this film was sheared, the strength of the crystal-crystal interactions in the oil phase became important. However, when Tween-40 was in the aqueous phase instead of the protein, the crystal-crystal interactions were not relevant, presumably because the Tween-40 interfacial film simply flowed around the adsorbed crystals     

Microchannel Emulsification Using Stainless‐Steel Chips: Oil Droplet Generation Characteristics

The first stainless‐steel microchannel (MC) emulsification chips with grooved MC arrays, each consisting of uniform‐sized parallel channels and a terrace, were developed. These chips enabled successful spontaneous‐transformation‐based generation of uniformly sized droplets of soybean oil and silicone oil. As for the influence of the dispersed‐phase velocity in a channel, the critical velocity below which uniform‐sized droplets were obtained from the channels depended on the interfacial tension between two phases. The maximum productivity of uniform‐sized oil droplets for the stainless‐steel MC emulsification chips was estimated to be several milliliters per hour. An adapted capillary number that considers the wettability of the dispersed phase of two different oils could be useful for understanding the flow state of the dispersed phase during droplet generation.     

驱油剂对三元复合驱含油污水中油滴稳定性的影响

三元复合驱技术已在大庆油田成功进行工业化应用。三元复合驱含油污水中由于含有残余的化学药剂，导致其很难处理，从而限制了三元复合驱技术的推广。本文首先采用室内实验制备模拟三元复合驱含油污水，然后通过沉降实验研究驱油剂对油滴稳定性的影响，最后结合驱油剂对油水界面张力、油滴Zeta电位、油滴粒径大小的影响来阐释驱油剂对油滴稳定性的作用机制。结果表明：油滴的稳定性随着NaOH浓度的增大先增大后减小，当NaOH浓度由0增大到400mg/L时，NaOH与原油中的酸性物质反应生成表面活性剂增强油滴的稳定性；当NaOH浓度大于400mg/L时，NaOH本身作为电解质压缩双电层，使油滴的稳定性减小。油滴的稳定性随着表面活性剂浓度的增大而增大，这是因为表面活性剂可以吸附在油滴表面，使油水界面张力减小，同时增大油滴表面的Zeta电位，从而使油滴的稳定性增强。油滴的稳定性随着聚合物浓度的增大先减小后增大，当聚合物的浓度小于300mg/L时，聚合物的桥接、絮凝作用起主导作用，聚合物分子可以吸附到油滴表面，将油滴连接到一起，同时聚合物分子可以压缩液滴表面的双电层，从而有利于油滴的聚结；当聚合物的浓度大于300mg/L时，体系的黏度增大，油滴的运动速度减小，此时聚合物分子占满油滴表面，表现出空间位阻作用，从而使油滴的稳定性增强，不利于油滴的聚结。     

Estimation of solid-liquid ratios in bulk fats and emulsions by pulsed nuclear magnetic resonance

Several pulsed nuclear magnetic resonance (NMR) methods were evaluated to estimate the solid fat content of fats and oil-in-water emulsions. The methods were checked with samples of paraffin oil or triolein containing known quantities of crystalline tristearate. A method based on the signal of solid fat (with use of a correction factor, the “f-factor”) was rejected in this work for general use. Correct results were obtained with methods that used only the signal of the liquid phase. With emulsions, disturbances could arise due to the surfactant present and to possible solubilization of water in the oil phase, presumably by monoglycerides. Without these disturbances, solid fat content in emulsions could be estimated as in bulk fats, after correction of the liquid phase signal for the contribution of protons from the aqueous phase. The signal from fat crystals inside emulsion droplets differed from that of crystals of the same fat in bulk, which may have been due to difference in crystal size but not to difference in crystal modification. Measurements on natural cream showed that disturbances were also possible in this type of emulsion.     

CFD analysis of microchannel emulsification: Droplet generation process and size effect of asymmetric straight flow-through microchannels

Asymmetric straight flow-through microchannel (MC) arrays are high-performance MC emulsification devices for stable mass production of uniform droplets. This paper presents computational fluid dynamics (CFD) simulation and analysis of the generation of soybean oil-in-water emulsion droplets via asymmetric straight flow-through MCs, each consisting of a microslot and a narrow MC. We also used CFD to investigate the effects of the channel size and the flow of the dispersed phase on MC emulsification using asymmetric straight flow-through MCs with a characteristic channel size of 5–400 μm. The overall shape of an oil–water interface and the time scale during droplet generation via a control asymmetric straight flow-through MC were appropriately simulated. Better insight was obtained on the flow profile of the two phases and the internal pressure balance of the dispersed phase during droplet generation. Comparison of the CFD and experiment results also provided insight into dynamic interfacial tension during droplet generation. Successful droplet generation was observed below a critical dispersed-phase velocity. In this case, the resultant droplet size was proportional to the channel size and was not sensitive to the dispersed-phase velocity applied. The maximum droplet generation rate per channel was inversely proportional to the channel size, unless the buoyancy force did not promote droplet detachment. The maximum droplet productivity per unit area of an asymmetric straight flow-through MC array was estimated to be constant, regardless of channel size.     

Interfacial Crystallization of Diacylglycerols Rich in Medium‐ and Long‐Chain Fatty Acids in Water‐in‐Oil Emulsions

The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.     

波纹板间油滴的Stockes浮升模拟分析

在分析油滴的Stockes浮升原理的基础上,应用Fluent6.0就波纹板间连续相入口速度、油滴粒径对Stockes浮升轨迹的影响,计算了多种工况,得到了油滴在波纹板间能否浮升到上板面聚集变大,除了取决于连续相的入口速度外,还取决于油滴的粒径。模拟结果表明,连续流场速度大小对油滴的Stockes浮升时间影响不太,浮升时间主要与油滴粒径有关,其计算结果为聚结波纹板的优化设计提供理论参考。     

电场作用下双液滴聚合特性

乳状液破乳分离是目前高含水期油田开采过程中难以解决的技术问题,电场破乳方法具有高效清洁等优点,是解决该问题的有效手段。采用数值模拟与试验验证相结合的方法研究电脱水过程中阶跃、斜坡电场诱导下双液滴的聚合与分离特性。结果表明,在斜坡电场作用下,界面张力引起的泵吸作用大于电场力引起的颈缩作用,有利于液滴聚并,且液滴发生二次乳化现象的概率降低。而施加阶跃电场时,一定范围内能够达到液滴破乳的目的,但液滴在聚并过程中易发生二次乳化现象。从电场对连续相影响的角度分析发现,阶跃电场不仅对液滴具有驱动作用,对连续相的影响也较为明显,阶跃电场会增大连续相内湍流作用,不利于电脱水过程。因此,采用斜坡信号诱导液滴聚合能够降低二次乳化现象发生的概率。     

AN EXPERIMENTAL STUDY OF DISPERSED LIQUID/LIQUID TWO-PHASE UPFLOW IN A PIPE

This paper presents experimental data for dispersed liquid/liquid upflows. Water was the continuous phase and mineral oil was the dispersed droplet phase. For this flow regime reduced gravity bubbly flow phenomena was simulated because the mineral oil and water had almost the same density. The mean velocity and turbulence fields, the size distributions of the oil droplets, the volume fraction, and interfacial area density distribution were measured using fiber optic Laser Doppler Anemometer (LDA) and phase Doppler Anemometer (PDA) systems. Significantly, the results presented in this paper are similar to those for bubbly air/water flows in microgravity conditions (Kamp el at., 1995).     

Formation and Microstructures of Whipped Oils Composed of Vegetable Oils and High-Melting Fat Crystals

This paper reports the experimental results of processes used for the formation of whipped oils composed of vegetable oils (salad oil) and high‐melting fat crystals [fully hydrogenated rapeseed oil rich in behenic acid (FHR‐B)]. No emulsifier was added to form this whipped oil. Microprobe FT‐IR spectroscopy, synchrotron radiation microbeam X‐ray diffraction (SR‐μ‐XRD), polarized optical microscopy, and differential scanning calorimetry (DSC) were employed to observe fine fat crystal particles of the most stable polymorph of β (β‐fat crystal), FHR‐B, and their adsorption at the air–oil surface before, during, and after the formation of the whipped oil. The results obtained revealed the following: (1) The preparation of an organogel composed of salad oil and small fibrous β‐fat crystals using a special tempering procedure was a prerequisite for forming whipped oil. (2) The β‐fat crystals were adsorbed at the air–oil surface to encapsulate the air bubbles during the formation process of whipped oil. (3) The values of overrun of the whipped oil reached >200 % after an aeration time of 30 min at 20 °C. (4) The SR‐μ‐XRD experiments demonstrated that the lamellar planes of the β‐fat crystals near the air–oil surface were arranged almost parallel to the air–oil surface plane. The present study provides the first evidence that tiny fat crystal particles may cause aeration in liquid oils without the addition of other whip‐assisting substances such as emulsifier crystals.     

Aging Effects on Surface Properties and Coalescence of Bitumen Droplets

The coalescence of emulsified bitumen droplets is examined, from the perspective of material surface properties, at temperatures of 22°C and 40°C over exposure periods of up to 8 h. The study was undertaken to better understand the nature of oil sands ore conditioning in the water‐based bitumen extraction processes of Syncrude Canada Ltd. Measurements of the bitumen droplet electrophoretic mobility showed only a slight degree of variation with temperature. The mechanical stress‐strain behaviour of the droplets was investigated using a micropipette‐based technique. These results indicate that the interfacial dilational elasticity of bitumen droplets depends on temperature and droplet age, while the tension is relatively invariant to duration of exposure. Interaction experiments between emulsified bitumen droplets quantify a coalescence probability that correlates with dilational elasticity at their surfaces.     

Lecithins in oil-continuous emulsions. Fat crystal wetting and interfacial tension

Lecithin is a powerful emulsifier widely used in foods, feeds and pharmaceuticals. Several analytical methods have been proposed to characterize lecithins, but they are often inadequate to determine the industrial functionality. The purpose of this study was to find a relationship between the interfacial properties of lecithins (adsorption to oil/water and fat crystal/oil/water interfaces), phospholipid composition and functionality. Results show that all lecithins adsorb to fat crystals at the triglyceride oil/water interface, making their surface more polar (observed as an increase in the contact angle measured through the oil at the interface: fat crystal/oil/water). This adsorption process is quick (less than five minutes) for relatively polar lecithins, such as soybean phosphatidylcholine (PC), and results in highly polar surfaces (contact angle ∼180°). Less polar lecithins give slow adsorption (some hours) and less polar crystals (contact angle ≤90°). The adsorption of different lecithins to the oil/water interface, observed as a decrease in interfacial tension, follows the adsorption pattern to the fat crystals. We found a relation between high-fat crystal polarity and poor lecithin functionality in margarine (margarines spatters during frying), and also between high-fat crystal polarity and a high polar to nonpolar phospholipids [Σ(PI + PA + LPC)/ΣPE; PI, phosphatidylinositol; PA, phosphatidic acid; LPC, lysoPC, PE, phosphatidylethanolamine] ratio in lecithin. The correlations might bevia aggregation properties of lecithin in the oil. We found also that monoolein shifted the adsorption kinetics of lecithin (soybean PC) to fat crystals and the hydrophilicity of adsorbed layers probably due to formation of mixed aggregates between monoolein and soybean PC.     

Preparation of monodispersed emulsion with large droplets using microchannel emulsification

Microchannel (MC) emulsification is a novel technique for producing monodispersed emulsions with coefficients of variation of less than 5%. To produce emulsions with large droplets, we designed three MC with large dimensions. The MC structure consists of two parts: a channel and a terrace. Terrace length was defined as the length from the exit of the MC to the end of the terrace. The MC plates used in this study have deeper channels and longer terraces. The size limit of droplets prepared by MC emulsification was studied. Monodispersed emulsions with droplets as large as 100 μm were prepared using an MC with a depth of 16 μm and a terrace length of 240 μm. The average diameter (coefficient of variation) of the emulsion droplets was 98.1 μm (2.5%). Emulsions with larger-diameter droplets were prepared using an MC with a longer terrace. The effect of the applied pressure on emulsification behavior was studied and discussed from the viewpoint of the droplet formation mechanism. At low applied pressures, droplet diameters were independent of the applied pressure, and monodispersed emulsions were produced. The pressure ranges of constant droplet diameter for large-droplet emulsions were narrower than those for the 5 to 30 μm droplet size emulsions because interfacial tension is more significant on a smaller scale compared with the other forces.     

Relationship between characteristics of oil droplets and solidification of thermally treated creams

The relationship between the characteristics of oil droplets and the change in appearance of cream was investigated. The model creams (40 wt% oil-in-water emulsion), similar to commerical products, were prepared with vegetable fat, milk protein, and emulsifier. The thermal treatment, in which the cream was exposed to a certain temperature and subsequently recooled, was performed on the assumption that the temperature was temporarily elevated during transportation and storage of commercial products. Solidification of the cream was observed when it was exposed to a temperature where there was a small percentage in solid fat content (SFC) of fat in oil droplets and recooled, whereas the cream remained in the liquid state when it was exposed to the temperature where SFC was zero and recooled. When the SFC of oil droplets was 0% at the treated temperature, greater supercooling prior to fat crystallization occurred and the crystallization rate after the initial formation of crystals was much higher. On the other hand, the polymorphism of fat in the droplets was not directly affected by the thermal treatment. These results indicate that the crystallization in oil droplets at the heating temperature may be closely connected with the destablization of oil droplets via a partial coalescence mechanism, which will cause the solidification of cream.     

Coalescence behaviour of water droplets in water‐oil interface under pulsatile electric fields

In this research, the deformation of water droplets in sunflower oil-interface under pulsatile electric field was studied experimentally. Three types of coalescence were observed:(i) complete coalescence, (ii) incomplete coalescence and (iii) no-coalescence. The first type is desirable because of leaving no secondary droplets. The second type that produced secondary droplets which caused by necking process, due to extreme elongation of droplets (mostly small droplets), was undesirable; because the small droplets were more difficult to coalesce and remove. The no-coalescence was caused by very fast coalescence and extensive pushing of droplet into the continuous phase. In this work the process was operated with the utilization of a batch cylindrical separator with high voltage system. The lower part of the cylinder was filled with the aqueous phase and its top part was filled with sunflower oil to form an interface between the two phases. The effects of electric field strength, frequency, and waveform types were investigated. It was found that, the ramp-ac waveform was the best waveform, avoiding the production of secondary droplets and in this case the frequency also played an important role.     

孔径梯度分布对亲油型滤材气液过滤性能的影响

在天然气净化、大型旋转机械曲轴箱通风和压缩空气过滤等领域,气液聚结过滤器具有广泛的应用。利用滤材过滤性能实验装置,分析了气液过滤过程中不同孔径梯度分布的亲油型滤材的压降、穿透率和饱和度变化,比较了其过滤性能、内部液体分布特性以及对液滴二次夹带现象的影响。结果表明：在气液过滤过程“通道压降”阶段,孔径递增滤材压降和0.8 μm以上液滴穿透率的变化曲线具有明显的分层特征。不同孔径梯度分布滤材的稳态过滤性能存在明显差异,主要原因是滤材内部存在液体运移通道的传递现象。通过与孔径递减和孔径均匀分布滤材的稳态过滤性能对比,发现孔径递增滤材在保证较低压降的同时具有最高的品质因子,有利于减少液滴二次夹带现象的发生,且对0.8 μm以上不同粒径液滴均具有最高的过滤效率,即孔径递增滤材在气液聚结过滤器设计中更具优势。     

Continuous-phase fat crystals strongly influence water-in-oil emulsion stability

To elucidate the role of continuous-phase fat crystals on emulsion destabilization, water-in-canola oil emulsions prepared with 0–2% (w/w) added solid fat (hydrogenated canola stearine or hydrogenated cottonseed stearine) were examined using pulsed NMR droplet-size analysis, sedimentation, and microscopy. Droplet-size analysis showed that addition of either fat prior to emulsification (precrystallized fat) or fat quench-crystallized in situ following emulsification (postcrystallized fat) decreased the degree of droplet coalescence, based on volume-weighted (d ₃₃) mean droplet diameters, with postcrystallized emulsions being more stable against coalescence. Sedimentation studies corroborated these results, with greatly enhanced stability against sedimentation in postcrystallized emulsions. Precrystallized fat had very little effect on emulsion sedimentation at levels as high as 2% (w/w). Postcrystallized cottonseed stearine produced slightly less resistant emulsions than did canola stearine, even if both were in the β-form. Surface energetics revealed that canola stearine had greater affinity for the oil/water interface and hence a greater displacement energy. The presence of micronsized (Pickering) crystals located directly at the droplet interface, resulting from in situ crystallization or generated by the shearing of precrystallized fats, provided enhanced stability vis-à-vis preformed crystals. These stabilized emulsions via the formation of crystal networks that partially immobilized droplets.     

工艺参数对层状液晶乳液结构的影响

讨论了由聚氧乙烯醚失水山梨醇脂肪酸酯、失水山梨醇脂肪酸酯、直链脂肪醇和挥发性物质组成的层状液晶乳液的制备过程中乳化时原料的加入顺序、乳化时间、冷却时搅拌速度及冷却时间对乳液的形态(脂质体结构,洋葱结构),特别是对乳液颗粒的粒径及粒径分布的影响。结果表明:乳化过程的时间对粒径的分布无明显影响;将水加入到含表面活性剂的油相中有利于形成完整结构的液晶乳液;冷却过程中的搅拌速度及搅拌时间对粒径的影响最大,为了得到较大颗粒为主的粒径分布,较佳冷却条件是搅拌速率在1 500 r/min、冷却60 min;慢速冷却有利于形成层间距较大的层状液晶,快速冷却易形成层间距略小的层状液晶。