Precision emulsification for droplet and capsule production

Emulsions and microcapsules are typical structures in various dispersion formulations for pharmaceutical, food, personal and house care applications. Precise control over size and size distribution of emulsion droplets and microcapsules are important for effective use and delivery of active components and better product quality. Many emulsification technologies have been developed to meet different formulation and processing requirements. Among them, membrane and microfluidic emulsification as emerging technologies have the feature of being able to precisely manufacture droplets in a drop-by-drop manner to give subscribed sizes and size distributions with lower energy consumption. This paper reviews fundamental sciences and engineering aspects of emulsification, membrane and microfluidic emulsification technologies and their use for precision manufacture of emulsions for intensified processing. Generic application examples are given for single and double emulsions and microcapsules with different structure features.     

Analysis of rotating membrane emulsification performance for oil droplet production based on the Taylor vortices approach

Membrane emulsification processes generally employ a cross flow of the continuous phase in order to produce shear stress. Modification of membrane emulsification for the o/w emulsion using the rotating system has been introduced such as the use of stirred cells or a rotating tubular membrane in a stationary liquid. This paper presents an examination of membrane rotation speed on droplet characteristics. The performance of rotating membrane emulsification on o/w droplet size, the coefficient of variation, and size distribution was investigated. In addition, the operated flow regime in the rotating membrane emulsification is addressed. It has been found that overall the droplet size decreased with the increase of membrane rotation speed. The droplet size below the pore size could be produced when operating at a high rotation speed (1500?rpm). The decrease of droplet size was believed due to the action of Taylor vortices on droplet detachment. Analysis of membrane rotation speed proposed that action of Taylor vortices facilitates droplet detachment. Calculation of Taylor numbers (having a value of 0–629) confirmed that the rotating membrane emulsification produced laminar flow with vortices.     

乳状液制备新工艺——膜乳化过程实验研究

用膜乳化系统制备了Ｏ／Ｗ型乳状液,考察了乳化时间、平均膜孔径、壁面剪应力、膜两侧压差和乳化剂等因素对乳化效果的影响．实验显示,分散相液滴平均直径不随乳化时间而变化;在此条件下,该直径约是膜平均孔径的５～１２倍．随着连续相一侧壁面剪应力的增大液滴平均直径减小,但当壁面剪应力大到一定值后,减小的幅度变得很小．增大膜平均孔径和膜两侧压差都将增加分散相透过膜的通量．此外,乳化剂分子的吸附速度越快,分散相液滴平均直径越小．     

Preparation of monodisperse W/O emulsions using a stainless-steel microchannel emulsification chip

In this study, hydrophobically treated stainless-steel microchannel (MC) array chips were used for preparing monodisperse W/O emulsions. A water-saturated decane containing 5?wt% tetraglycerin monolaurate condensed ricinoleic acid ester was used as the continuous phase. A Milli-Q water containing 5?wt% polyethylene glycol (molecular weight 20,000) and 5?wt% NaCl was used as the dispersed phase. The stainless-steel MC array chips used for MC emulsification had a sufficiently high contact angle of the dispersed phase to their surface in the continuous phase. The resultant uniform-sized aqueous droplets with a coefficient of variation of <5% had average diameters of 100–300?µm, depending on the MC cross-sectional size. The maximum productivity of uniform-sized aqueous droplets reached higher than 1?mL?h^?1. The difference in the critical capillary number of the dispersed phase that flows in a 100-µm depth MC was 1.5 times greater than that in a 30-µm depth MC.     

Free jets spun from a prilling tower

A mathematical model of the dynamics of an inviscid liquid jet, subjected to both gravity and surface tension, which emerges from rotating drum is derived and analysed using asymptotic and computational methods. The trajectory and linear stability of this jet is determined. By use of the stability results, the break up length of the jet is calculated. Such jets arise in the manufacture of pellets (for example, of fertilizer or magnesium) using the prilling process. Here the drum would contain many thousands of holes, and the molten liquid would be pumped into the rotating drum. After the jet has broken up into droplets, these droplets solidify to form pellets. The jets in this prilling process are curved in space by both gravity and surface tension.     

厌氧膜生物反应器在食品废水处理中的应用研究

分别采用小试规模(50 L/d)外置错流管式厌氧膜生物反应器和中试规模(20 t/d)浸没式厌氧旋转膜生物反应器进行了食品厂废水的处理实验研究.结果表明,加入超滤膜单元提高了厌氧系统的总有机物去除率及甲烷产量,使系统出水水质更加稳定;外置错流式超滤膜随运行时间的延长通量明显下降,而旋转式超滤膜可通过膜片旋转速度提高和保持膜通量;浸没式旋转膜组件的运行能耗较外置管式膜组件至少降低30%;但不同形式的厌氧膜生物反应器对氨氮和总磷去除能力有限,需进一步处理.     

Dielectrophoresis of reverse phase emulsions

Reverse miniemulsions, emulsions of droplets of size 200 nm-1 microm of a polar liquid dispersed in an apolar continuous liquid phase, exhibit strong electrokinetic responses in low-frequency electric fields. The electrokinetic behaviour of a reverse miniemulsion, previously developed for use as electronic paper, has been investigated under static and flow conditions, in uniform and non-uniform electric fields. Results reveal that when using frequencies lower than 10 Hz strong aggregation of the droplets occurs. In uniform electric fields, under static conditions, droplets reversibly aggregate into honeycomb-like or irregular aggregates. Under flow conditions, droplets aggregate into approximately equidistant streams. In non-uniform electric fields the droplets reversibly aggregate in high-field regions, and can be guided along regions of high field strength in a flow. The potential of the technique for the formation of structured materials is discussed.     

DVB泡沫微胶囊的制备方法

根据密度匹配乳液技术设计开发了一套用于微胶囊制备的三喷嘴乳粒发生器,利用该装置实现了空心泡沫微球的可控连续制备。以二乙烯基苯(DVB)的邻苯二甲酸二丁酯(DBP)溶液为油相(O),双蒸水与重水的混合液为内水相(W1),质量百分比为5%的聚乙烯醇(PVA)水溶液作为外水相(W2)制作出水/油/水(W1/O/W2)双重微乳液。以偶氮二异丁腈(AIBN)为引发剂,通过水平旋转水浴加热方式使DVB凝胶固化,采用CO2超临界法干燥,最终制得直径(1.0mm～4.0mm)和壁厚(90μm～360μm)可调的DVB微胶囊。利用扫描电镜对微胶囊的形貌进行了研究,并归纳出影响微胶囊的粒径大小及单分散性的因素。     

Monodisperse, Submicrometer Droplets via Condensation of Microfluidic-Generated Gas Bubbles

Microfluidics (MFs) can produce monodisperse droplets with precise size control. However, the synthesis of monodisperse droplets much smaller than the minimum feature size of the microfluidic device (MFD) remains challenging, thus limiting the production of submicrometer droplets. To overcome the minimum micrometer-scale droplet sizes that can be generated using typical MFDs, the droplet material is heated above its boiling point (bp), and then MFs is used to produce monodisperse micrometer-scale bubbles (MBs) that are easily formed in the size regime where standard MFDs have excellent size control. After MBs are formed, they are cooled, condensing into dramatically smaller droplets that are beyond the size limit achievable using the original MFD, with a size decrease corresponding to the density difference between the gas and liquid phases of the droplet material. Herein, it is shown experimentally that monodisperse, submicrometer droplets of predictable sizes can be condensed from a monodisperse population of MBs as generated by MFs. Using perfluoropentane (PFP) as a representative solvent due to its low bp (29.2 °C), it is demonstrated that monodisperse PFP MBs can be produced at MFD temperatures >3.6 °C above the bp of PFP over a wide range of sizes (i.e., diameters from 2 to 200 μm). Independent of initial size, the generated MBs shrink rapidly in size from about 3 to 0 °C above the bp of PFP, corresponding to a phase change from gas to liquid, after which they shrink more slowly to form fully condensed droplets with diameters 5.0 ± 0.1 times smaller than the initial size of the MBs, even in the submicrometer size regime. This new method is versatile and flexible, and may be applied to any type of low-bp solvent for the manufacture of different submicrometer droplets for which precisely controlled dimensions are required.     

Nanoemulsions as delivery systems for lipophilic drugs

Nanoemulsions have received a growing attention as colloidal drug carriers for pharmaceutical applications. Their advantages over conventional formulations include drug enhanced solubility and bioavailability, protection from toxicity, improved pharmacological activity and stability, more sustained delivery and protection from physical and chemical degradation. Nanoemulsions can be prepared by two major techniques, high-energy and low-energy emulsification. Both these emulsification methods have proved to be efficient to obtain stable nanoemulsions with small and highly uniform droplets. Further research into nanoemulsions is important to develop novel liquid formulations with more efficient results in therapeutic.     

Polymer dispersion preparation by flow induced phase inversion emulsification. Part 1 The effect of silica on emulsification and dispersion characteristics

Low density polyethylene (LDPE) melt was emulsified in the presence of a hydrophobically modified water soluble polymer (HMWSP) and colloidal hydrophilic silica using the Flow Induced Phase Inversion (FIPI) emulsification technique. HMWSP was used as the surface active material. After the emulsification, LDPE melt was solidified to obtain a polymeric dispersion. Silica was used to aid the emulsification and improve the emulsion/dispersion characteristics. It was shown that the presence of silica increases the amount of aqueous phase necessary for phase inversion from water-in-LDPE melt to LDPE melt-in-water emulsion. The mean particle size and particle size span increased in the presence of silica. However, due to broader particle size distribution, the viscosity was lowered. The dispersions with silica appeared to form a more uniform film compared with the dispersion without silica. When the silica concentration is less than 1% in aqueous phase, an emulsion is obtained. At 2% silica level, a wet powdery material is obtained. This material can be diluted to obtain a dispersion or it could be used in powder coating.     

酵母中小分子糖渗滤特性研究

根据纳滤过程和渗透原理数学模型,采用一元线性方程推导出料液和渗滤液中葡萄糖、海藻糖浓度与累积渗透体积的指数曲线,并对糖浓度的实测值和预测值进行比较.经过渗滤处理,葡萄糖和海藻糖回收率分别达86.96%和83.64%,而其他低聚糖损失率小于3%,指数方程能较好预测渗滤过程浓度变化.     

基于脉冲微孔喷射的液滴沉积成型

基于脉冲微孔喷射法(POEM)开发均匀液滴喷射成型设备,可实现均匀微熔滴的逐滴三维沉积,并通过一系列实验研究一维柱沉积时微熔滴沉积位置的准确性以及一维线沉积时平台运动速率对微熔滴结合的影响。结果表明:微熔滴的沉积具有可重复性并且沉积位置准确;当平台运动速率为600μm/s时,微熔滴间的结合良好,表面光滑无明显缺陷。最后进行简单立体薄壁制件的沉积,制件结构稳定,熔滴排布均匀,因此该方法可实现金属均匀微滴的沉积成型。     

High-throughput single copy DNA amplification and cell analysis in engineered nanoliter droplets

A high-throughput single copy genetic amplification (SCGA) process is developed that utilizes a microfabricated droplet generator (microDG) to rapidly encapsulate individual DNA molecules or cells together with primer functionalized microbeads in uniform PCR mix droplets. The nanoliter volume droplets uniquely enable quantitative high-yield amplification of DNA targets suitable for long-range sequencing and genetic analysis. A hybrid glass-polydimethylsiloxane (PDMS) microdevice assembly is used to integrate a micropump into the microDG that provides uniform droplet size, controlled generation frequency, and effective bead incorporation. After bulk PCR amplification, the droplets are lysed and the beads are recovered and rapidly analyzed via flow cytometry. DNA targets ranging in size from 380 to 1139 bp at single molecule concentrations are quantitatively amplified using SCGA. Long-range sequencing results from beads each carrying approximately 100 amol of a 624 bp product demonstrate that these amplicons are competent for achieving attomole-scale Sanger sequencing from a single bead and for advancing pyrosequencing read-lengths. Successful single cell analysis of the glyceraldehyde 3 phosphate dehydrogenase (GAPDH) gene in human lymphocyte cells and of the gyr B gene in bacterial Escherichia coli K12 cells establishes that SCGA will also be valuable for performing high-throughput genetic analysis on single cells.     

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Suppressing vortex-induced vibration (VIV) has recently attracted numerous researchers due to its practical significance in many engineering applications. Most of the previous studies have focused on a passive or active flow control. A structurally active control approach to mitigate a two-dimensional, nonlinear coupled, cross-flow/in-line VIV has not been well studied. This paper presents a reduced-order fluid-structure dynamic model and combined analytical–numerical solutions for the efficient suppression of two-dimensional VIV of a flexibly mounted circular cylinder in uniform flows. The theoretical model is based on the use of coupled Duffing–Rayleigh oscillators with three variables describing the cylinder cross-flow/in-line displacements and the strength of the fluid vortex circulation in the cylinder wake. These equations of fluid-structure motions contain geometric and hydrodynamic nonlinearities. Closed-loop linear and nonlinear velocity feedback controllers are implemented in the transverse direction governing the larger cross-flow response than the associated in-line counterpart. Approximated analytical expressions are derived by using the harmonic balance to explicitly capture the system nonlinear dynamic features and the effects of key dimensionless parameters. Parametric investigations are carried out to evaluate the linear versus nonlinear controller performance in terms of the maximum response suppression capability and the power requirement in a wide range of reduced flow velocities, mass ratios, and control gains. Over the main lock-in resonance region with coupled cross-flow/in-line responses, the linear controller is found to be more efficient in suppressing the two-dimensional VIV by also modifying the system frequencies and phase relationships. Nevertheless, based on the power comparison, the nonlinear control is superior to the linear control for very small targeted controlled amplitudes of a very low-mass cylinder. These active control strategies may be further applied to the multimode VIV suppression of a long flexible cylinder with multi degrees of freedom.     

Preparation of ethylene vinyl acetate copolymer latex by flow induced phase inversion emulsification

Ethylene vinyl acetate (EVA) copolymer was emulsified in the melt state using hydrophobically modified water soluble polymers (HMWSPs) as surfactants and the flow induced phase inversion (FIPI) emulsification technique. The history of the emulsification and emulsion structure were monitored using a process rheometer and off-line scanning electron microscopy and particle size measurements. It was shown that low molecular weight surfactants could not be used to emulsify the polymer melt. When HMWSPs were used, the emulsion characteristics were strongly influenced by the molecular structure of the surfactant. Water-in-polymer melt emulsion was phase inverted to polymer melt-in-water emulsion at 20% water phase volume. When this emulsion was allowed to cool after further dilution (30% water) while mixing, a second phase inversion took place to obtain a water-in-polymer dispersion which has the consistency of a powder. When this dispersion was re-heated, while mixing, a third phase inversion occurred and a multiple emulsion system was obtained. Upon the solidification of the polymer, the structure of the dispersion was revealed as (water-in-polymer)-in-water. Water continuous latex from the first phase inversion and the powdery emulsion from the second phase inversion can be used in coating applications while the third phase inversion produces micro-porous polymer.     

Influences of combustion improver content and motionless time on the stability of two-phase emulsions

The heavy molecular bonds of liquid fuels can be broken with the assistance of a nitromethane fuel additive by virtue of its explosive and flammable properties to obtain greater heat release. Because of the immiscibility between nitromethane and petro-diesel, two-phase emulsions of nitromethane dispersed in the oil phase of a mixture of diesel and biodiesel were prepared. The experimental results show that microwave irradiation produced an emulsion with a larger number of dispersed nitromethane droplets in the continuous oil mixture, a smaller mean droplet size, and lower turbidity than magnetic stirring, and thus was a better method for preparation of the two-phase emulsion. The increase in the nitromethane weight fraction increased the number of dispersed nitromethane droplets and the emulsion turbidity. In addition, allowing the emulsion preparation to remain motionless for a longer period of time after either method resulted in an obvious reduction in the emulsification stability (ES).     

含油污水陶瓷膜处理工艺的数值模拟

陶瓷膜污水处理技术近年来在油田含油污水领域得到了迅速发展,跨膜压差、处理温度以及油滴和悬浮颗粒的浓度都直接关系到膜处理时对离散相粒子直径的选择性和处理效果.运用Fluent计算软件在微观上对含油污水的处理条件(包括跨膜压差、温度以及含油污水的浓度)进行了数值模拟研究,结果表明,在适当的跨膜压差下,提高污水处理温度,减小含油污水浓度(进行污水预处理)可以减小膜污染的程度,从而明显地提高污水处理的效果.     

Titania nanospheres from supercritical fluids

Surfactant-coated amorphous titania nanospheres have been synthesised using templating 'water-in-supercritical carbon dioxide' emulsion droplets; the process represents a clean and controlled method for the manufacture of high-purity nanoparticles.     

Droplet‐Based Microreactors for Continuous Production of Palladium Nanocrystals with Controlled Sizes and Shapes

Droplet‐based microreactors are used for the continuous production of Pd nanocrystals. Specifically, commercially available polytetrafluoroethylene (PTFE) tube and silica capillaries are utilized to fabricate a fluidic device capable of generating water‐in‐oil droplets. In addition to the feasibility of using such droplets as microreactors for conducting a synthesis, the ability to control the composition and concentration of reagents by adjusting the flow rates is demonstrated; reagents are mixed by periodically pinching the PTFE tube, and nanocrystals are produced with uniform size distribution in a continuous fashion. The capability to tailor the size and shape of the resultant nanocrystals is further demonstrated by introducing the reducing agent and capping agent at different flow rates to control the nucleation and growth processes. The ability to transform a bulk synthesis into a droplet‐based system holds great potential for the development of a new route to the high‐volume production of nanocrystals.