用激光散射技术测定硝酸铵微滴的分解

在常温常压下,一个初始半径为5～30μm的硝酸铵水溶液微滴被悬浮在电动平衡仪内,同时该微滴受到一束激光的照射.在34.5°～68.4°散射角内使用一个512点线性光电列阵,测定不同时间里硝酸铵微滴的光散射强度变化.借助于计算机上Mie理论计算,可以容易地比较出硝酸铵微滴的尺寸.根据这种方法,可以精确地测定硝酸铵微滴在分解蒸发过程的尺寸变化.在实验基础上,提出了一个扩散控制的表面反应模型以描述硝酸铵微滴的分解蒸发过程,并得到硝酸铵微滴在25℃、26℃和27℃时的平衡压力.     

气溶胶微滴的蒸发及界面现象

用电动平衡仪和光散射技术研究气溶胶微滴蒸发及其伴随的界面现象.研究的系统有缓慢蒸发的有机物微滴、快速蒸发的水滴和含表面活性剂的水滴.实验结果表明:蒸发速率影响着微滴的温度;表面活性剂显著地降低了水滴的蒸发速率;表面电荷密度的增加会导致微滴的分裂.这些研究结论对控制工业装置中液滴的蒸发和燃烧过程有着重要意义.     

超细丙烯酰胺液滴光化聚合反应

在电动平衡仪中悬浮单个带电荷的丙烯酰胺单体或丙烯酰胺单体-甘油微滴。微滴约50μm直径受到两束激光照射。通过测量一束激光的弹性散射,可精确测定微滴的尺寸的变化。另一束激光是用来提供荧光的激发能。微滴中含有微量荧光物(Auramine-O),它的荧光光谱可以揭示微滴中的聚合反应过程。聚合反应会导致蒸发速率降低。测量微滴的蒸发过程,并用一个同时考虑蒸发和聚合反应的数学模型,就能计算出聚合反应速率常数。     

双散射角光学粒子计数器测量气溶胶折射率

本文提出了60°和90°双散射角OPC测量气溶胶折射率的新反演方法.利用60°和90°双散射角OPC样机进行了气溶胶折射率和粒子大小谱分布的实际测量.与滤膜取样积分片方法和Vaisala的能见度仪的测量结果对比表明,利用60°和90°双散射角OPC测量气溶胶折射率和谱分布结果是合理的,双散射角OPC方法是可行的.     

沉淀剂对超声雾化法制备CeO2纳米颗粒的影响

利用硝酸铈为原料,分别以碳酸氢铵和氢氧化钠为沉淀剂,采用超声雾化法制备了CeO2纳米颗粒.在室温将反应液体在超声雾化器中雾化成微滴,然后把微滴作为微反应器,使粒子在体积有限的微液滴内成核、晶化、长大.利用X射线衍射仪、Fourier红外变换仪、透射电镜对所制得样品的物相、结构和形貌进行了表征.结果表明:利用超声雾化法制备CeO2纳米粒子的颗粒均匀且分散性较好;以氢氧化钠为沉淀剂较以碳酸氢铵为沉淀剂制备的CeO2颗粒更均匀,粒径更小,约为3nm.     

卤化银乳剂微晶体的结构与性能研究 Ⅵ.八面体核壳乳剂的壳厚对微晶体的光吸收和电性质影响

应用双注仪制备了碘含量为30 mol％的碘溴化银乳剂微晶体,然后采用二次乳化法形成外壳,制备出核壳比分别为1:1,1:2,1:3,1:4的一组核壳乳剂。采用X射线能谱法对乳剂单个颗粒进行微区成份分析,证明乳剂微晶存在富碘核与贫碘壳,且随核壳比的增加。颗粒外缘碘离子浓度减小;应用UV-240紫外可见光度计和微波光导仪测定了乳剂微晶的光吸收和光电导。测量结果表明,由于碘含量减小与颗粒直径增加两因素的影响,乳剂的光吸收能量大致相同;随核壳比的增加,乳剂的光电导估号上升;当核壳比等于1:3时,光电子寿命最长。对乳剂的感光性能与上述各种性质的关系进行了讨论。     

以四氧化锇固定氯乙烯乳液

测定乳液聚合中单体微滴的大小是有意义的。与有些单体如苯乙烯和烷基丙烯酸酯不一样,在标准状况下氯乙烯呈气体状态。因此,使用任何常规方法测定微滴的大小是困难的。特别是当微滴小于1微米时就更加困难了。     

聚乳酸微球的制备工艺研究

以聚乳酸为基础材料,选择聚乙烯醇为乳化剂,采用O/W乳化-溶剂挥发法制备形态较好的聚乳酸微球.在可确定因素固定下来后,在保证成球质量的基础上,分别通过调节乳化剂的浓度和其它因素在一定范围内来控制微球的平均粒径.单因素实验结果表明,PLA浓度、乳化剂浓度、搅拌速度、滴加速度对微球性能影响显著.通过正交实验得出制备粒径大小为100 μm左右聚乳酸微球的最佳工艺方案为:搅拌速度600 r·min-1,PLA浓度9%(g·mL-1),PVA浓度0.5%(g·mL-1),滴加速度1.5 mL·min-1.     

玻璃料滴温度的测量

介绍了用光电温度计自动测量料滴表面温度的方法及其在实际应用中的情况。实践表明,用光电温度计配上快速显示记录仪,能连续、快速、准确地测量料滴温度。     

卤化银乳剂微晶体的结构与性能研究 Ⅶ.切角立方体乳剂微晶体的核壳复合结构

本工作应用双注仪制备了一系列不同碘含量的切角立方体核壳乳剂,用紫外光度法测定了它们的光吸收,用介电损耗法和微波光导法分别测定了它们的离子电导及光电导。结果表明,乳剂微晶体的光吸收和离子电导率都随着碘含量的增加而增加,光电导也随碘含量增加而增大,光电子衰减遵循二级反应动力学过程。碘的引入以及立方体切角使立方体乳剂微晶体的感光性能成倍地增长。     

T型微流控芯片中微液滴破裂的数值模拟

利用VOF模型对T型结构微流控芯片中微液滴的三维破裂过程进行了数值模拟,获得了液滴发生破裂和不会破裂两种流型。一定轴向长度的微液滴对应着一个临界毛细数,当主流流体的毛细数大于此临界毛细数时,微液滴发生破裂并分别流向T型结构两侧;否则不会发生破裂,微液滴流向任意一侧。通过多个工况的计算,拟合了临界毛细数与微液滴相对轴向长度的关系,探讨了黏度比对微液滴破裂的影响。发现黏度比越小,微液滴越易发生破裂。     

Preparation of tritium breeding Li2TiO3 ceramic pebbles via newly developed piezoelectric micro-droplet jetting

Wet methods as an emerging technique for the preparation of millimeter-sized tritium breeding ceramic pebbles, but the imposed air pressure as the driving forces to extrude slurry droplets are fluctuating during the reciprocating extrusion process, which caused a slight inconsistency in pebble sizes. In this study, a piezoelectric micro-droplet jetting approach was proposed by introducing a piezo-driven valve and modifying the slurry barrel mechanism to realize the air pressure invariable. A self-developed piezoelectric micro-droplet jetting device was successfully utilized to prepare Li₂TiO₃ green pebbles with coefficients of variation being lower than 2.7%. The size of the green pebbles could be precisely controlled in the range of 0.88–1.37 mm by manipulating the nozzle diameter, the air pressure, and the jetting time. The pebbles sintered at 1000°C for 3 h possessed a small grain size of ∼5.9 μm, a satisfied relative density of ∼84.8% T.D., and a high crush load of ∼25.7 N, implying the prepared pebbles could be used as a promising solid tritium breeding material in fusion reactors. These findings are anticipated to provide new opportunities for the highly efficient preparation of size-controllable tritium breeding ceramic pebbles.     

用化学交联法制备聚(4-乙烯基吡啶)纳米凝胶微球

在1,1,2-三氯乙烷/甲醇混合溶剂中用碘代甲烷使聚(4-乙烯基吡啶)(P4VP)线性高分子部分季铵化后，在水中制成微乳液，并用1,4-二碘丁烷交联剂对P4VP微乳液内部进行化学交联，得到固化凝胶微球. 考察了部分季铵化比率、交联温度以及聚合物浓度对微球直径和直径分布的影响，发现微球直径随季铵化比率的增加、交联温度的增加及聚合物浓度的减少而减小. 当季铵化比率为75%(摩尔比)、交联温度为60℃、聚合物浓度为1.0%(w)时，得到了直径为20 nm、粒径分布为±15%的凝胶微球. 本研究的重要特征是不加入任何乳化剂也能得到很小的纳米凝胶微球.     

Droplets generation under different flow rates in T-junction microchannel with a neck

The 2D top view of the droplet formation in microfluidic T-junction devices with a neck is recorded to estimate the droplet volume under different flow conditions. The channel with a neck at the T-junction, to provide a narrow structure, is proposed but has not been analyzed as the normal T-junction. The droplet generation process is separated into two stages, including the filling stage and the squeezing stage, to develop a droplet size predictive model based on the continuity of both liquids. In a wide range of flow conditions for multiphase microfluidics, this study validates and physically explains the model by analyzing the generation of droplets and coefficients of the model. Results of this study can help to design droplet microfluidic devices, where it is requisite to know the relation between flow conditions and the droplet size.     

The liquid–liquid flow dynamics and droplet formation in a modified step T-junction microchannel

The droplet generation mechanism in the asymmetrically enhanced step T-junction remains unknown, especially for the transition stage from dripping to jetting regimes. In this work, the droplet generation mechanism was systematically investigated in a modified step T-junction by modulating a large flowrate range and altering different interfacial tensions. We found that under different fluid regimes, both the capillary number and flow rate ratio of continuous and dispersed phase showcase completely different impacts over droplet generation. In dripping regime, the interfacial tension, which was controlled by changing the surfactant concentration, dominated the formation mechanism when the surfactant concentration was found below micelle concentration. In jetting regime, our experimental results showed that the influence of the surfactant concentration on the size of generated droplets was rather negligible while the flow rate ratio of continuous and dispersed phase indeed determined such a parameter. In the dripping-jetting transition stage, an increase of droplet size was observed despite the increase of continuous phase flow. After reaching a peak, the droplet dimension started to decrease with the increase of continuous phase flow as expected. To the best for our knowledge, it is the first study to report generation mechanism in modified step T-junction from dripping to jetting regimes.     

Fabrication of composite microcapsules by drop-on-demand inkjet: Effect of precursor composition on the process limits

The feasibility of using drop-on-demand inkjet technology for the fabrication of calcium alginate hydrogel microcapsules containing dispersed sub-micron solid particles (TiO₂ photocatalyst) was demonstrated. The influence of the printed solution viscosity on the micro-droplet size has been investigated and a study of the effect of solids fraction in the suspension on its printability was carried out. It was found that solutions with viscosities of up to 28 mPa s and solids content of up to 7.8 vol% can be reproducibly printed, resulting in droplets ranging from 45 to 105 μm depending on the inkjet operating conditions. In order to ensure stable and reproducible droplet formation, a pressure difference ranging from −200 to −1800 Pa had to be maintained in the nozzle. A uniform distribution of dispersed solids in the resulting microcapsules was achieved by adjusting pH and viscosity. The relationship between the printhead operating pressure, the fluid viscosity, the solids loading and the final size of the obtained microcapsules was established, allowing rapid prototyping of artificial cell-like structures with internal solid inclusions by the inkjet method.     

Preparation of ZrO2 beads by an improved micro-droplet spray forming process

Monodisperse ZrO₂ ceramic beads with size larger than 1 mm have been prepared by an improved micro-droplet spray forming process, through which a compressor and a dispenser were employed to produce droplets continuously. Furthermore, the slurry recipe and drying temperature have been optimized to enhance the sphericity and smoothness of the beads. The sintered ZrO₂ ceramic beads present promising mechanical performance, including a relative density of 84.6%, a crush strength of 256.2 ± 36.6 N as well as a Vickers hardness of 1344.4 ± 58.3 HV. Such procedure reveals great potential in mass production of ceramic beads.     

微流控芯片中微滴的形成及其在生物医学分析中应用

微流控芯片微滴技术具有可形成粒径均匀可控的微滴,能实现试剂快速混合、反应通量高、样品组分间无交叉污染等优点。综述微流控芯片中微滴的形成方法及微滴技术在生物分析及化学领域的应用研究进展。     

高效氯氟氰菊酯微乳剂的制备及其液径尺寸

[目的]为了考察微乳剂和乳油剂型的液径(MDS)尺寸和稀释喷洒后的农药形态,使用复合乳化剂和乙酸丁酯溶剂,制备了质量分数为3.0％的高效氯氟氰菊酯微乳剂(ME).经测试,各项性能达到国家标准.[方法]用激光光散射仪研究了不同水稀释倍数对3％高效氯氟氰菊酯微乳剂的MDS、多分散指数(PDI)和Zata电位值的影响,以2.5％高效氯氟氰菊酯乳油(EC)作为对比.[结果]研究发现MDS随不同稀释倍数稍微增大,且微乳剂的MDS/小于乳油剂型.放置时间对其液径的影响显示21后微乳剂不同稀释倍数的液径均在100 nm以下.对2种剂型的30 mg/L稀释液,经喷施和干燥后进行扫描电镜观察.[结论]微乳剂形成棒状或块状结晶,晶体尺寸在几微米到十几微米范围;而2.5％高效氯氟氰菊酯乳油则形成树枝状结晶,晶体尺寸在50 μm以上,这对药效发挥不利.