Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

The rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.     

Dynamic behaviour of drops in oil/water/oil dispersions

The dynamic behaviour of drops of oil/water/oil (O/W/O) and water/oil (W/O) in abnormal polymer/water/surfactant systems was investigated. The size of internal oil droplets continuously decreased with time until it reached a steady-state value. Whereas the size of multiple water drops showed a minimum. After the minimum, the size of multiple water drops either reached a steady-state value or continued enlarging until phase inversion occurred. The phase inversion occurred because inclusion of oil droplets into water drops resulted in a continuous increase in effective volume fraction of dispersed phase. The time evolution of the size of multiple drops was described in terms of a balance between (a) drop break-up and escape and (b) drop coalescence and inclusion. The inclusion events retarded the initial decrease in the size of multiple water drops with time and increased the drop size after the minimum. By reducing the surfactant concentration, the ability of the dispersed phase to entrain the continuous phase decreased so that no minimum was achieved for the size of multiple drops with time, similar to conventional systems with simple drops. The size distribution of the multiple water drops initially narrowed and then widened again, whereas the size distribution of internal oil droplets continuously narrowed with time until it reached a constant value. Generally, the size distribution of drops narrowed as the average size of drops decreased. The possible mechanisms for complex drop formation were discussed and drop deformation was suggested as the main cause for inclusion at a low dispersed phase ratio.     

Influence of Different Silica Nanoparticles on Drop Size Distributions in Agitated Liquid‐Liquid Systems

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.     

An experimental study of Mesler entrainment on a surfactant‐covered interface: The effect of drop shape and Weber number

Mesler entrainment is the formation of large numbers of small bubbles which occurs when a drop strikes a liquid reservoir at a relatively low velocity. Existing studies of Mesler entrainment have focused almost exclusively on water as the working fluid in a nominally clean state, where even very small levels of contamination can cause significant changes in surface tension that affect the repeatability of the results. Herein water combined with the soluble surfactant Triton X‐100 is used as the working fluid in an attempt to stabilize the state of the water surface. Despite this approach, nominally identical drops did not always result in the same bubble formation event. Accordingly, Mesler entrainment was quantified by its frequency of occurrence for drops having the same nominal diameter and impact velocity. This frequency of occurrence was found to be well correlated to both the Weber number and the shape of the drop on impact. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

In situ visualization of drop deformation,erosion, and breakup in high viscosity ratio polymeric systems under high shearing stress conditions

In this paper, deformation and breakup under simple shear of single molten polymer drops in a polymer matrix were investigated. Flow visualization was carried out in a Couette‐Flow apparatus under relatively high shear rates and temperatures up to 230°C. Drop/Matrix combinations were composed of polystyrene drops of 0.5–0.6 mm in diameter in polyethylene matrix, and ethylene–propylene copolymer drops of approximately the same size in polypropylene matrix. The deformation and breakup processes were studied under steady state and time‐dependent shearing conditions. Either for steady state or time‐dependant shearing conditions, drop elasticity generated at relatively high shear rates helped the drops to align perpendicular to the flow direction, i.e., parallel to vorticity axis. Also, the most striking non‐Newtonian effects for the high viscosity ratio systems were the surface erosion and the drop splitting mechanisms. The particles eroded off the main droplet surface were very fine, in the range of 10–50 μm, and led to a significant reduction in main drop size before its final breakup. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2582–2591, 2006     

Interactions between two in-line drops rising in pure glycerin☆

The behaviors of time-dependent interaction between two buoyancy-driven in-line deformable drops rising in pure glycerin at Re b 1 were studied, where the diameter for the leading drops ranged from 9.51 mm to 12.6 mm and for trailing drops from 12.7 mm to 15.8 mm. The situation while a larger drop chasing a smal er one was specifically considered which typical y led to the smal er drop“coating”the larger one. Two approaches, the geometric feature approach and the energy change one, were used to judge the starting and ending times of the interaction between two drops. Based on a conical wake model, the drag coefficient of two approaching drops was calculated. Due to the approaching effect of the trailing drop, the leading drop was accelerated and the average drag coefficient was smal er than that for a free rising single drop. The frequency spectrums of the lateral oscillation of two drops during the interaction were obtained by using Fourier analysis. The oscillation frequency of the interactional drops was also different from that for a free rising single drop because of the wake effect produced by the leading drop. Due to a superposition of the drop shape oscil ation and the drop internal circula-tion, the transverse oscil ation frequencies of two drops have the same trend during the approaching process. ? 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

The dynamics of single air bubbles and alcohol drops in sunflower oil at various temperatures

Steady rises of a single air bubble, a methanol drop, and an ethanol drop in a vertical glass column of refined sunflower oil at temperatures of 25, 30, 40, and 50°C are investigated experimentally using photography. The Reynolds numbers obtained are 0.07–16, 0.02–13.43, and 0.017–11.18 for the air bubbles, methanol drops, and ethanol drops, respectively. Results for terminal velocity and drag coefficient are compared with the selected existing correlations for bubble and drop motions in immiscible liquids. Correlations by Rodrigue show good agreement for various bubble sizes and system temperatures. Experimental drag coefficients of methanol and ethanol drops show a systematic deviation from the Oliver and Chung and the Darton and Harrison correlations, respectively. Considering the effect of dissolution of alcohol in vegetable oil, which varies with temperature, on the drop dynamics, semiempirical correction factors are applied to the last two correlations to fit the experimental results. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Morphology of micron‐sized,monodisperse, nonspherical polystyrene/poly(n‐butyl methacrylate) composite particles produced by seeded dispersion polymerization

Nonspherical polystyrene (PS)/poly(n‐butyl methacrylate) (PBMA) composite particles with uneven surfaces were produced by seeded dispersion polymerization of BMA with 1.65‐μm, monodisperse, spherical PS seed particles. The composite particles consisted of a PS core and an incomplete PBMA shell. The formation mechanism of such nonspherical particles was discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2013–2021, 2002     

Contact of a spherical particle with a droplet

The collection of particles by liquid drops is profoundly influenced by the contact angle of the particles with the drops and the surface tension of the drops. The present investigation was undertaken to establish an equation with reference to the force which acts on a particle by surface tension after contact of a particle with a drop, and to simplify its solution. Moreover, the approximate equations obtained can be applied as regards the arbitrary contact angle of a particle with a drop and the arbitrary ratio of the radius of the drop to the particle. The agreement between theoretical and experimental values could be verified by this experiment.It is considered from these results that the approximate equations can be utilized when it is necessary to know the behaviour of a particle after contact with a liquid drop.     

ON THE EFFECTIVE CONDUCTIVITY OF A DILUTE SUSPENSION OF SPHERICAL DROPS IN THE LIMIT OF LOW PARTICLE PECLET NUMBER

In this paper we consider the effective conductivity of a dilute suspension of neutrally bouyant spherical drops which is undergoing a simple shear flow. The thermal conductivity, viscosity and specific heat capacity of the drops are assumed to be different from those of the suspending fluid, though it is assumed that the local Peclet and Reynolds numbers are small both inside and outside the drop. The analysis consists of three parts: a derivation of the relationship between bulk heat flux on the one hand and the thermal and momentum fields at the microscale of the suspended particles on the other; a calculation of the local temperature field near a single neutrally buoyant spherical drop in shear flow with an imposed transverse temperature gradient at large distances; and a synthesis of the general relationship for bulk heat flux and the calculated local temperature field to determine an effective conductivity for a dilute suspension of spherical drops.     

A NOTE ON LIGHT TRANSMISSION THROUGH AN EVOLVING SUSPENSION OF LIQUID DROPS

The intensity of light transmitted through an evolving suspension of two-dimensional deformable liquid drops in shear-driven or pressure-driven flow within a channel with parallel-sided walls is studied using a numerical method. The rays enter the suspension normal to upper wall, undergo reflections and refractions at the drop interfaces, and either return to the upper wall or leave from the lower wall. The motion and deformation of the drops are computed using a boundary integral method, and the optics is studied using a standard ray-tracing method. Evidence is presented that, in the case of shear-driven flow, a consistent correlation exists between the intensity of light transmitted through the channel, the geometry of the microstructure, and the global rheological properties of the emulsion. In the case of pressure-driven flow, a correlation between the transmitted intensity and the effective viscosity is also observed, but its features are not entirely consistent. These differences are attributed to the profound effect of variable flow rate or presence of a mean pressure drop on the state of the microstructure and accompanying dynamical features of an emulsion.     

Inducing arbitrary vapor pressures,and quantifying leakages

We generalize the Maxwell drop evaporation equation to cover the range from closed system to open system through semiclosed system where the evaporation is restricted to an arbitrary degree which we show how to characterize. We first consider a suspended drop, and then a drop contacting a surface where the surface's vicinity restricts the evaporation paths. We show how to use these results to obtain arbitrary values of vapor pressure by simple manipulations of the numbers and sizes of droplets added to the system for a constant leak size, or, alternatively, control the leak size with a valve for given sizes of drops. We further show how to use this result to quantify a leakage in a system. Such a leakage is characterized using a single parameter (leakage length) which the described method calibrates. The calibrated leakage length can be used for systematic control of vapor concentrations within the chamber. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4548–4553, 2016     

罐底油三相分离理论及实验研究

介绍了罐底油的现状及罐底油中渣颗粒和油滴及水在离心力场中的运动规律、受力情况,建立了相应的物理模型;推导出了渣颗粒的离心沉降分离速度、沉降层厚度和油滴的向心分离速度、向心层厚度的表达式;通过小型实验设备对罐底油进行了三相分离实验研究,分析了温度、分离转数等对分离效果的影响。实验与理论分析结果基本吻合,为罐底油的简单有效分离提供了依据。     

微细圆管及扁平管内液-液Taylor流动特性的数值研究

微细通道内Taylor流动广泛应用于能源化工领域,为分析其相界面及阻力特性,利用相对坐标系的方法,研究了竖直圆管及扁平管内的液-液Taylor流动,讨论了通道宽高比、Reynolds数（Re）及分散相体积分数对液膜厚度和两相压降的影响。结果表明：圆管内液滴头部和尾部可以膨胀至近似球形,而扁平管内壁面的限制作用较强,液滴呈现扁平状。随Reynolds数增大,两相界面逐渐收缩,液膜厚度逐渐上升。圆管内液膜厚度比较均匀,扁平管内液膜在通道顶部较薄,而圆弧部分较厚。两相压降随Re和宽高比的增大而增大,随分散相体积分数的增大而降低。相比连续相和分散相压降,界面压降所占的比重最高,并依据模拟结果,提出了圆管及扁平管内液-液Taylor流动的压降预测公式。     

The behaviour of large gas bubbles at a liquid-liquid interface. Part 2: Liquid entrainment

The roles played by large gas bubbles in the generation and coalescence of liquid drops at a liquid-liquid interface are elucidated. The amount of lower liquid entrained by individual bubbles and the resulting drop size distributions in the upper liquid phase are quantified for the three phase system: sunflower oil + 50 wt % decane, water + 50 wt % sugar, air, and qualitative theoretical models are presented. Drops settling to the interface were found to coalesce rapidly and bubble flux had no apparent effect on the rate of drop coalescence at the liquid-liquid interface.     

智能响应型Pickering乳液的制备及在物质分离中的应用进展

Pickering乳液是指由微纳米固体粒子代替传统表面活性剂作为乳化剂而稳定的乳液,具有较强的稳定性和超高油/水界面,能够为多相界面反应和物质传输提供高效稳定的场所。Pickering乳液的乳滴结构和性质与固体颗粒的尺寸形貌及表面性质密不可分,通过调控固体颗粒本身或表面的性质可以赋予Pickering乳液特定的响应性功能,拓宽其应用领域。本文对近年来不同响应型（磁性、CO₂、pH、光、温度等响应型）的Pickering乳液的主要研究成果进行了综述,重点介绍了Pickering乳液的稳定性原理、响应型Pickering乳液的制备方法和结构调控策略,以及近年来Pickering乳液在物质分离提取中的应用研究进展,最后对智能响应型Pickering乳液应用研究的发展趋势进行了展望。     

The effect of hydrodynamic parameters on the production of Pickering emulsions in a baffled stirred tank

Pickering emulsions are potential industrial scale alternatives to surfactant-based emulsions. The stability of Pickering emulsions depends on the physicochemical nature of the liquid–particle interface and the hydrodynamic conditions of the production process. This article investigates the effect of hydrodynamic conditions on the drop size of concentrated Pickering emulsions in baffled stirred tanks. Oil in water emulsions composed of silicon oil, water, and hydrophilic glass beads as stabilizing particles were produced. Two impellers were used at different sizes: Rushton turbine (RT) and pitched blade turbine. The effects of power per mass, Reynolds number, tip speed, and Weber number on the droplet sizes were studied. The energy dissipated around the impeller and the size of the impeller high shear zone were found to be critical to the emulsion droplet sizes. The breakup and droplet-particle contact mechanism of the RT was found to be more favorable for the production of the Pickering emulsions.     

小儿氨酚烷胺滴鼻剂的工艺研究

采用不同溶剂进行溶解情况筛选小儿氨酚烷胺滴鼻剂的处方工艺,合理处方进行药效学研究.处方的较佳辅料为:1,2-丙二醇:水=1:1的混合溶剂,该滴鼻剂具有较好的解热、镇痛和抗炎作用,无刺激性,配制工艺简单,使用方便,疗效确切,值得进一步研究.     

The tough microcapsules of acrylic acid–styrene–isoprene–styrene quadrablock copolymer shell via Pickering emulsion technique

Pickering emulsion technique has been demonstrated a simple method to fabricate the microcapsules. However, the resulted microcapsules are often fragile. This limits their applications. Here, we report that the microcapsules with the nanostructured shell of poly(acrylic acid‐b‐styrene‐b‐isoprene‐b‐styrene) (ASIS), which is of high toughness and elasticity, could be fabricated via Pickering emulsions using ASIS nanoparticles as stabilizing particles. The surfactant‐free ASIS latex (with theoretical molecular weight for each block: 1.5k–15k–55k–10k) was synthesized by reversible additional fragmentation transfer (RAFT) emulsion polymerization using amphiphilic macro‐RAFT agent [poly(acrylic acid)₂₀‐b‐polystyrene₅ trithiocarbonate] as both reactive surfactant and polymerization mediator. It was found that the ASIS nanoparticles were able to self‐assemble on oil/water interface to stabilize Pickering emulsion of hexadecane in the pH range from 8 to 12. The droplet diameter was finely tuned from 17 to 5 µm by increasing the ASIS particle levels from 0.13 to 12 wt % based on the mass of the ASIS aqueous dispersions. With toluene as a coalescing aid, the capsules with a coherent and nonporous shell were obtained with the dispersed phase volume percentage as high as 50%. The toluene treated capsules were so mechanically strong to survive the utrasonic treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46700.     

Sessile drops: Do they really stand on solid surfaces?

Bangham and Razouk [1] have described the decrease in free energy at a solid-vapor interface on adsorption of vapor to the solid from zero pressure (vacuum) to any pressure up to p^o, the saturation vapor pressure. Derjaguin and Zorin (DZ) [2] have proposed adsorption isotherms of vapor to solid surface which cross the p^o line and then return to p^o to form sessile drops. Adamson and coworkers [3] have presented a theory to generate a DZ type isotherm and point out that the isotherm implies formation of an autophobic layer on all solid surfaces that support sessile drops. Schrader and Weiss [4] have proposed an adsorption isotherm for sessile drop formation which crosses the p^o line but does not return to p^o on formation of the sessile drop. This last approach does not require ubiquitous formation of autophobic layers on solid surfaces in sessile drop systems. Free energy isotherms based on the last approach are presented to describe film formation (Type 1 free energy isotherm), sessile drop formation on low-energy surfaces (Type 2), and sessile drop formation on autophobic layers (Type 3). The approach also enablcs derivation of a new equation for the vapor pressure of sessile drops subject to contact angle hysteresis.