掺氮TiO_2纳米颗粒稳定的Pickering乳液制备及其触发酶反应

利用烷基硅烷接枝的掺氮TiO_2纳米颗粒稳定W/O型Pickering乳液,研究了TiO_2掺氮量对成乳的影响以及乳液的可见光响应性能,并将其作为微反应器应用于触发脲酶催化尿素生成碳酸铵的反应中。结果表明:在可见光照射下,烷基硅烷接枝的掺氮TiO_2纳米颗粒表面由疏水变为亲水,可引发乳液液滴聚并以及液滴内酶促反应发生。     

月桂酸改性氧化锌纳米颗粒的Pickering乳化性能研究

研究了不同程度月桂酸表面改性氧化锌纳米颗粒的Pickering乳化性能。通过调节月桂酸用量来改变氧化锌纳米颗粒表面亲疏水性(接触角θ),并探讨了不同接触角氧化锌纳米颗粒稳定的Pickering乳液的乳滴粒径、相转变及稳定性变化规律。结果表明,部分亲水的氧化锌纳米颗粒稳定(三相接触角40°～60°)的O/W型乳液具有最小的液滴尺寸和最优的稳定性。在最优条件下利用Pickering乳液聚合法制备了表面负载氧化锌纳米颗粒的有机硅弹性微球,粒径为5～20μm。     

微流控乳液模板法构建功能微颗粒过程中介尺度结构定向调控的研究进展

功能微颗粒材料因其微型化和多功能化等优点而在诸多领域具有广泛的应用。微流控技术可控制备的多样化乳液液滴体系为功能微颗粒材料的创新设计与可控制备提供了优良而独特的模板。深入研究乳液模板法构建功能微颗粒材料过程中介尺度结构的形成与演变规律,以及液滴界面介尺度结构与乳液动力学行为、界面传质与反应耦合对微颗粒介尺度结构的影响规律等,对于实现乳液模板结构调控与新型功能微颗粒材料创新制备具有重要意义。本文主要综述了微流控乳液模板法构建功能微颗粒过程中介尺度结构定向调控的研究进展,着重涵盖了两方面内容：（1）微流控法可控制备乳液模板的过程中,液滴界面两亲分子聚集态介尺度结构的调控与液滴运动、吞并、融合、相界面定向演变等动力学行为之间的相互影响关系和调控机制,以及上述调控对液滴形貌、结构和组成的影响规律;（2）乳液模板制备功能微颗粒的过程中,界面传质、反应,及两者耦合对微颗粒介尺度结构的定向调控,以期为新型功能微颗粒材料的高效制备与性能强化提供科学指导。     

利用有机化凹凸棒石颗粒制备W/O型Pickering乳液

选取我国储量丰富的凹凸棒石矿,对其表面进行十六烷基三甲氧基硅烷有机改性处理,将制备的纳米颗粒应用于乳液的制备。系统考察了体系pH、颗粒质量分数和油相体积分数等因素对Pickering乳液稳定性的影响。结果表明:随着分散体系pH的增加,乳液液滴尺寸先增大后减小又增大再减小;随着颗粒质量分数的提高,可用于稳定乳液的颗粒数量增多,乳液稳定性提高;随着油相体积分数的增大,乳液液滴尺寸先增大后减小又增大再减小。通过调节水相体系的pH,成功制备了由有机改性凹凸棒石颗粒单独稳定的W/O型乳液。     

液-液两相流体黏度对微通道内流型的影响

为了研究流体黏度对液-液两相流流型的影响，采用实验和数值模拟相结合的方法,研究十字型微通道内液-液两相流流型变化。结果表明，当两相流体系中存在高黏度流体时，会加剧两相界面的不稳定性，两相流流型极易向不规则流和环状流转换，且当连续相流体黏度较高时，液滴的形状更易为子弹流。通过引入毛细数和韦伯数，提出两相流流型转换关系。当连续相流体和分散相流体分别由水平通道和垂直通道流入时，通过合理调节两相流体流速，可在微通道下游实现大小液滴的融合。这一方式将为高黏度流体流动操控提供新思路，通过控制两相流速，可以实现不依赖于复杂微通道结构的液滴被动融合。     

微通道中原位分散技术可控制备氧化铜纳米流体及复合薄膜前体

疏水纳米颗粒分散于有机体系中形成的纳米分散体,具有独特的理化性质和重要的应用价值。其中,纳米颗粒的单分散性、均匀性和稳定性是决定纳米分散体性能的关键。以CuO纳米分散体作为纳米流体和复合薄膜前体这一典型体系为研究对象,通过设计平板型微通道实现了CuO纳米分散体制备过程中的液滴聚并和改性CuO纳米颗粒的原位分散。制备了颗粒体积分数达2%、平均粒径约30 nm的CuO-基础油纳米流体,该纳米流体具有良好的稳定性和达到0.184 W·m^-1·K^-1的较高热导率;制备的CuO-PDMS（聚二甲基硅氧烷）复合薄膜具有较强的抗菌性能和颗粒复合层稳定性。通过系统性实验研究,证明了原位分散方法在强化改性颗粒高效分散中的重要作用,确定了颗粒性能及分散行为对分散体性能的影响规律。     

微通道内传递对液液分散过程的影响规律

在同轴环管微通道中,采用水/正辛醇形成两相体系,利用硫酸向水中传质并释放热量以实现伴随传质传热的微分散过程,研究了两相流速、硫酸浓度对两相流型和液滴大小的影响规律。结果发现,传递会引发O/W/O新流型的产生和流型分布区域变化。探讨了传递强度对于分散液滴尺寸的影响,通过计算液滴脱落时的动态界面张力,分析了传质和传热对于液液微分散影响的大小。     

微流控技术中液滴聚并的研究进展

随着微流控技术的发展,在微通道内精确调控液滴行为的研究受到越来越多的关注。详细介绍了引发液滴聚并的方式,包括主动聚并和被动聚并。主动聚并是指施加电场、磁场、温度场等引起液滴融合,被动聚并是指通过改变通道结构或改变通道壁面润湿性促进聚并发生。此外,综述了液滴聚并动力学研究进展,例如：液膜排出时间和临界毛细管数。最后对聚并过程中的流场研究做了简要介绍。对液滴聚并的后续机理研究、探索高效的聚并方式和聚并的实际应用具有重要的指导意义。     

梳状并行微通道内液液分布规律研究

为了实现工业化应用,微反应器的并行放大已成为最有效的放大策略之一。在微反应器的放大过程中,相分布规律的研究是非常重要的。采用高速摄像仪研究了梳状并行微反应器的支通道间距和流量对液液两相分布的影响。当连续相和分散相流量Q_c及Q_d都较小时,不同支通道间距的微反应器内前方支通道的分散相含率较低,后方支通道的分散相含率较高,同时液滴长度的均匀性较差。随着Q_c与Q_d的增大,三种不同构型微反应器内分散相的体积相含率的数值分布逐渐趋于集中。在较高的两相流量下,支通道内液滴长度的均匀性显著提高,其变异系数小于0.15。在实验范围内,支通道间距S = 0.6 mm的微反应器中液滴尺寸均匀分布的操作范围最大。     

Alg@TiO2微球稳定的Pickering乳液用做防晒乳成分的研究

为了开发一种兼具防晒功能和乳液稳定性的防晒乳配方,设计了一种负载二氧化钛纳米颗粒的海藻酸钙微球（Alg@Ti O₂微球）来稳定Pickering乳液,用作防晒乳成分。考察了油水比和微球含量对Pickering乳液的影响,探究了乳液类型,并进行了长期保存稳定性测试。结果表明,Alg@Ti O₂微球形状为球形,大小为2～6μm;Alg@Ti O₂微球中二氧化钛纳米颗粒含量为43%;微球与油水的三相接触角为120°;当油水比为1∶1,微球含量为3%（w/%）时,稳定的白油/水体系Pickering乳液为油包水型（W/O型）,经100 d室温保存后乳液状态保持稳定。通过紫外吸收实验,和包括市售防晒乳在内的其他3种防晒乳相比,该Pickering乳液具有优异的防晒性能。通过皮肤表面清洗实验,该Pickering乳液具有易清洗的特性。     

Modeling of droplet-droplet interaction phenomena in gas-liquid systems for natural gas processing

The design of efficient gas liquid separation units for natural gas production lines depends on the accurate estimation of the droplet size distribution. The droplet size can be estimated by considering breakage and coalescence phenomena. In particular, off-shore separation units working at high pressure (100-200 bar) require special consideration of coalescence processes with multiple outcomes. This work discusses the introduction of multiple outcomes in the coalescence process. Numerical experiments are presented in order to highlight the effect of multiple coalescence behavior in the evolution of the droplet size distribution.     

Hydrophilic porous polymers based on high internal phase emulsions solely stabilized by poly(urethane urea) nanoparticles

Stable oil-in-water (o/w) Pickering high internal phase emulsions (HIPEs) having an internal phase of up to 95 vol% were prepared with a low-energy emulsification method. A poly(urethane urea) (PUU) aqueous nanodispersion was used as aqueous phase. The PUU nanoparticles of the aqueous nanodispersion acted as a mechanical barrier, and prevented droplet coalescence in the Pickering HIPEs. In addition, open porous hydrophilic polymer foams were obtained by polymerization of the Pickering HIPEs, and the morphology of the foams were tailored by changing the oil:water ratio, PUU nanoparticle and NaCl concentrations. The method used herein provides a simple way to prepare morphology controlled hydrophilic polymer foams using o/w Pickering HIPEs as template.     

Morphology evolution and dynamics of droplet coalescence on superhydrophobic surfaces

In this work, the coalescence of two equal‐sized water droplets on superhydrophobic surfaces (SHSs) is experimentally investigated. The morphologies of droplet coalescence are observed from side‐view and bottom‐view using high‐speed camera system. The related morphology evolution and dynamics of droplet coalescence are explored. The dynamic behaviors of droplet coalescence on SHSs can be decomposed into liquid bridge growth, contact line evolution, and droplet jumping. The liquid bridge radius is proportional to the square root of time, whereas the dimensionless prefactor is decreased from 1.18 to 0.83 due to the transition of interface curvature. The retraction velocity of the contact line shows limited dependence on initial droplet radii as the retraction dynamics considered here are governed by the capillary–inertial effect. The coalesced droplet finally departs the substrate with a dimensionless jumping velocity of around 0.2. A heuristic argument is made to account for the nearly constant dimensionless jumping velocity. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2913–2921, 2018     

Microdroplet coalescences at microchannel junctions with different collision angles

Microdroplet coalescence mechanism is very important for the miniaturization of multiphase chemical processes with microstructured devices. Using three working systems with different physical properties, this article presents an experimental study on the fluid dynamics of microdroplet coalescence at different microchannel junctions. The critical capillary number to distinguish coalescence or noncoalescence of microdroplet is investigated and its variations with droplet size, collision angle, and physical properties are analyzed with two important parameters – the film drainage time and droplet contact time. Experimental results indicate that microdroplet coalescence can be enhanced by reducing the droplet collision angle. The differences of microdroplet coalescences in confined microchannels and free‐flowing spaces are provided with the analysis of critical capillary number. A model equation is proposed to predict the critical capillary numbers in this study, which may provide valuable information for the design and development of new microstructured chemical device. © 2012 American Institute of Chemical Engineers AIChE J, 59: 643–649, 2013     

基于显微图像识别的微流控液滴聚并研究

微流控技术作为操控微米尺度液滴的重要手段,受到普遍关注。显微摄像是微流控过程的主要研究方法,以往主要通过人工观察识别的方式获取关键参数,工作效率低、数据量小,限制了针对复杂微流控过程的深入认识。提出了一种基于MATLAB图像处理程序的微流控液滴聚并研究方法,通过背景提取、背景扣除、掩膜二值化、噪声消除、区域填充、形态开启、边界物体移除、干扰滤除等过程,实现六边形扩大通道内液滴聚并显微实验视频的数值化,进一步通过识别液滴投影面积、质心、偏心率等信息,研究了液滴运动速度和液膜的排空时间等微流控聚并关键参数的变化规律。     

Hydrodynamics and morphologies of droplets coalescence on fiber

Fiber coalescence is an effective oil–water separation technology. In this article, the micro-coalescence process of droplets on fiber was studied through high-speed camera technology, and the hydrodynamics and morphology evolution in the process of droplet-fiber coalescence were explored and compared with non-fiber system. The results show that the change of the droplet surface morphology is local at the initial stage of the coalescence process. The droplet morphology changes obviously near the neck. The growth rate of the liquid bridge and the propagation speed of capillary wave in droplet-fiber system are higher than those in non-fiber system. At 0.8 ms, the capillary waves' polar angle difference between the two conditions reaches 10.44°. There is an obvious periodicity and damping attenuation mechanism in the oscillation process. In the droplet-fiber system, the oscillation process attenuates faster and the average oscillation period is shorter. The droplet relaxes to a stable state more quickly.     

Characteristics of Stable Pickering Emulsions under Process Conditions

Emulsions stabilized by solid particles are so called Pickering emulsions which are characterized by their high stability against coalescence. This type of emulsion can be used for a lot of applications. Very little is known about how reaction conditions affect their properties. In this study the influence of important reaction conditions like shear stress, pressure, temperature, and the influence of synthesis gas on Pickering emulsions is investigated. It is shown that the emulsions remain stable in terms of coalescence in a broad range of the reaction conditions and are suitable as reaction media for industrial processes and for a reaction optimization with a subsequent separation step.     

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.