溶液浓度和载气流量对气溶胶特性的影响

随着PM 2.5成为热点,PM 2.5口罩的测试手段也开始受到广泛关注,气溶胶粒子浓度及粒径分布则是口罩过滤效果测试中最重要的参数。为了使测试条件更为贴近口罩的实际工况,针对口罩测试中常用的NaCl固体气溶胶和DEHS油性气溶胶,探讨了气溶胶发生器的溶液浓度和载气流量对气溶胶粒子计数浓度及粒径大小特性的影响。结果表明,溶液浓度和载气流量对气溶胶粒子计数浓度有明显影响;NaCl溶液浓度对气溶胶的粒径大小有影响;载气流量对NaCl气溶胶的粒径大小无明显影响,而对DEHS气溶胶粒径大小有影响。     

n-BMA/MMA共聚核壳乳液的合成研究

通过半连续种子乳液聚合的方法,制备了具有核壳结构的丙烯酸酯聚合物乳胶粒子。采用甲基丙烯酸甲酯(MMA)、甲基丙烯酸酯正丁酯(n-BMA)等单体进行共聚。研究了共聚合过程中,乳化剂浓度、引发剂等对聚合物乳液粒径大小、凝胶量等的影响,并利用动态光散射(DLS)、透射电镜(TEM)和差示扫描量热仪(DSC)对乳胶粒子进行表征。结果表明:核乳液聚合阶段乳化剂浓度增大,乳液粒子的粒径变小,引发剂用量对粒径及分布影响不大;TEM观察到核乳胶粒径大小及变化趋势与DLS测得的结果相一致,并且核乳胶粒子和核壳乳液粒子都呈规则的圆球状,分布均一;DLS测试核壳丙烯酸酯乳胶粒子粒径的变化呈逐渐增长的趋势;DSC测试发现制备的核壳粒子有2个玻璃化转变温度(Tg),验证了胶乳粒子核壳结构的存在。     

溶析结晶法制备聚苯乙烯微粒

采用溶析结晶法制备了球形聚苯乙烯(PS)亚微米粒子,并用激光粒度仪、FESEM等分析方法对粒子大小、粒度分布以及粒子形貌等进行了表征,对料液浓度、搅拌速度、料液/反溶剂体积比、结晶温度对粒径的影响进行了考察.结果表明,溶析结晶法制备的PS粒子为球形,粒径分布比较窄,平均粒径在500nm左右,比文献报道的超临界流体技术法制备的PS颗粒小;料液浓度是影响粒径的重要因素,其他因素对粒径影响较小.     

浅谈稳定剂对MMA/MA分散共聚合的影响

以乙醇/水混合溶剂为分散介质,偶氮二异丁腈、聚乙烯吡咯烷酮和双甲基丙烯酸乙二醇酯分别为引发剂、稳定剂和交联剂进行了甲基丙烯烯酸甲酯/丙烯酸（MMA/AA）的分散共聚合研究。用透射电子显微镜和离心式粒径分布仪测定了粒子大小和粒度分布,重点讨论了稳定剂浓度对聚合速率,共聚物微球粒径及粒径分布的影响。发现随着稳定剂浓度的增加聚合速率增加,转化率提高,微球的粒径变小而分散性变好。     

稳定剂对MMA/MA分散共聚合的影响

以乙醇 /水混合溶剂为分散介质 ,偶氮二异丁腈、聚乙烯吡咯烷酮和双甲基丙烯酸乙二醇酯分别为引发剂、稳定剂和交联剂进行了甲基丙烯烯酸甲酯 /丙烯酸 (MMA/AA)的分散共聚合研究。用透射电子显微镜和离心式粒径分布仪测定了粒子大小和粒度分布 ,重点讨论了稳定剂浓度对聚合速率 ,共聚物微球粒径及粒径分布的影响。发现随着稳定剂浓度的增加聚合速率增加 ,转化率提高 ,微球的粒径变小而分散性变好。提出了该体系分散聚合的接枝稳定机理。     

超细TATB制备方法对粒子结构的影响

采用几种方法制备了超细TATB样品，并对粒子大小、粒径分布、粒子形状、孔容及孔隙分布等进行了表征。结果表明：亚微米TATB样品中有97％以上的粒子粒径小于0．2μm，气流粉碎法和合成法制备的样品粒子形貌呈球形，粒径分布宽，大小不均匀，表面有凹痕；重结晶法制备的样品粒子形貌呈条形，粒子大小比较均匀，粒径分布较窄，冷冻干燥有助于减轻超细粒子间的聚集。     

聚甲基丙烯酸甲酯共聚物微乳液粒径控制研究

本文对聚甲基丙烯酸甲酯共聚物微乳液聚合工艺、单体用量、反应型乳化剂、阴离子乳化剂用量及配比对粒子大小及分布的影响进行了研究。结果表明,通过半连续滴加聚合工艺制备的微乳液乳胶粒粒径小,分布窄;随着混合单体用量的增加,乳胶粒呈现粒径逐渐变大,分布逐渐变宽趋势;随着乳化剂用量的增加,乳胶粒径呈现不断减小的趋势;随着AA用量的增加,乳液的粒径及其分布呈增大的趋势。通过采用半连续滴加法获得了粒径大小可控(42.6~51.9 nm)的聚甲基丙烯酸甲酯共聚物微乳液。     

PSt乳胶纳米粒子的制备

采用乳液原子转移自由基聚合法,成功制备出了聚合物乳胶纳米粒子。用光子相关光谱(PCS)和透射电子显微镜(TEM)对聚合物乳胶粒子的形貌、粒径和粒径分布进行了表征,结果表明:聚合物乳胶粒子的粒径小于100nm。研究了乳化剂的用量对乳胶粒子粒径大小的影响,研究发现:聚合物乳胶粒子的粒径随乳化剂用量的增大而减小。     

相反转法水性环氧树脂的制备

以Span-80和SDS为复合乳化剂,将环氧树脂E-51用相反转法乳化成水包油的稳定乳液。研究了复合乳化剂的亲水亲油平衡值(HLB)、乳化剂的浓度以及乳化温度对环氧树脂E-51相反转点时含水量R_f值、乳液的粒径及粒径分布和乳液离心稳定性的影响,并通过透射电镜(TEM)对乳液粒子的大小、形貌进行表征。结果表明:当复合乳化剂的HLB值为16.2,即Span-80与SDS的质量比为2:1时,乳化剂的质量分数为9%,乳化温度为50℃时,得到的乳液稳定性最好,乳液粒子大小均匀、粒径分布较窄。     

聚氯乙烯糊树脂颗粒形态与增塑糊性能关系的研究

用激光散射法对聚氯乙烯糊树脂 (PPVC)浆料粒径及其分布和粉料颗粒粒径及其强度进行了测定和研究。结果表明 :初级粒子的粒径大小和分布是决定 PPVC树脂糊性能的关键因素 ;在一定范围内 (3 0～ 60μm) ,二次粒子颗粒强度即二次粒子的解碎程度是影响 PPVC树脂成糊性能的重要因素之一     

Measurement of the floating particle size distribution by a buoyancy weighing-bar method

The particle size distribution of cylinder-shaped solid particles was measured using a buoyancy weighing-bar method where the liquid phase density was adjusted to settle or float the particles. The particle size distribution obtained in our experiment agrees with the particle size measured by other method. The present study demonstrates that a buoyancy weighing-bar method, a novel method for measuring the particle size distribution, is suitable for measuring the particle size distribution of a floating solid. The precision of the resulting particle size distribution is comparable to that of a laser diffraction/scattering method as well as a direct measurement with a micrometer. Moreover, this buoyancy weighing-bar method can measure the particle size distribution even in a mixture of two particles with different sizes.     

Effect of particle size distribution on stress development and microstructure of particulate coatings

The role of pigment particle size distribution on stress and microstructure development was studied for coatings prepared from aqueous suspensions of ground calcium carbonate (GCC) and latex binder. Stress development was monitored using a modified beam deflection technique under controlled environment. Microstructure was characterized by scanning electron microscopy (SEM) and cryogenic SEM. For coatings containing only GCC particles and no latex, a wide particle size distribution resulted in a significant particle size gradient in the cross-sectional microstructure and irregular stress development. With latex addition, uniform microstructures were observed in coatings with either wide or narrow GCC particle size distribution. GCC/latex coatings prepared using GCC with a wide particle size distribution developed a higher stress than those prepared using GCC with a similar average particle size but a narrow particle size distribution. The higher stress is related to the particle packing that results in smaller pore sizes and larger capillary pressures that drive compaction. In coatings prepared with the same GCC particles but different latex binders, the stress and cracking behavior of the coating depends on the latex properties.     

水泥颗粒群粒度分布宽度的表征及其应用研究

用分形理论阐述了将水泥颗粒群粒度分布的分形维数作为定量表征其粒度分布宽度的正确性和可行性,测量了16种水泥颗粒群的粒度重量累积分布,在双对数条件下,水泥颗粒群的粒度重量累积含量与粒径之间呈直线关系,表明水泥颗粒群粒度分布结构具有分形特征,其分形维数可以定量表征水泥颗粒群粒度分布宽度;研究了水泥颗粒群粒度分布宽度与其空隙率的关系,结果表明,随着水泥颗粒群粒度分布宽度的增加,其空隙率减小,二者呈负相关。     

Optimizing the balance between viscosity/modulus and impact in particulate composites

The objective of this study was to develop some new concepts of importance when trying to optimize the viscosity/modulus and impact relative to the particle‐size distribution in suspensions and particulate composites. The results of this study appear to indicate that, conceptually, it is possible to significantly improve the viscosity versus the impact balance for material formulations by optimizing the particle‐size distribution. For binary particle‐size distributions, the influence of the preferred particle‐size distribution, as determined using a square‐root distribution, did not yield the most desirable particle‐size distribution if the particle‐to‐particle component of the interaction coefficient was high. However, if three or more particles were utilized in the distribution, then the optimum particle‐size distribution utilized can apparently be characterized using the square‐root distribution even when the particle–particle component, σ_pc, of the interaction coefficient, σ, was found to be quite high. In addition, this same square‐root particle‐size distribution can also satisfactorily predict a probability of impact that can remain consistently high as long as the particles utilized are well chosen and not too close in size. Thus, this preferred particle‐size distribution can be utilized to predict at least one of the preferred distributions to optimize the balance of properties between impact and the viscosity/modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 291–304, 2002     

THE EFFECTIVENESS FACTORS FOR VARIOUS SIZE DISTRIBUTIONS OF CATALYST PARTICLES

In general, catalyst beds are made up of a size distribution of particles. Often the distribution of particle sizes can be well represented by either a rectangular or triangular size distribution. This paper shows that characteristic mean particle sizes can be defined for both the rectangular and triangular distributions such that the effectiveness factor based on this single particle size lies close to the effectiveness factor for the distribution. Thus, by using the correct mean particle size a quick and reasonably accurate evaluation of the effectiveness factor for the particle size distribution can be made.     

纳米金溶胶的合成及紫外-可见吸收光谱的研究

在弱酸性或近中性条件下,用化学还原剂还原较高浓度的氯金酸溶液,制得纳米金种子溶液,然后用晶种法制备金溶胶。通过透射电镜、激光粒度分布仪等测定了纳米颗粒的粒径和分布情况,并对纳米金溶胶的紫外可见吸收曲线进行了研究。结果表明,以硼氢化钠为还原剂可以得到粒径小且分布均匀的产品,采用不同大小的晶种制备的纳米金颗粒的粒径不同,且随粒径变大紫外-可见吸收曲线上的最大吸收波长红移也越大,分布变宽。     

THE EFFECTIVENESS FACTORS FOR VARIOUS SIZE DISTRIBUTIONS OF CATALYST PARTICLES

In general, catalyst beds are made up of a size distribution of particles. Often the distribution of particle sizes can be well represented by either a rectangular or triangular size distribution. This paper shows that characteristic mean particle sizes can be defined for both the rectangular and triangular distributions such that the effectiveness factor based on this single particle size lies close to the effectiveness factor for the distribution. Thus, by using the correct mean particle size a quick and reasonably accurate evaluation of the effectiveness factor for the particle size distribution can be made.     

二项式分布在种群平衡模型模拟粒度分布中的应用

提出了一种适用于几何网格的子粒子二项式分布函数,并应用于种群平衡模型模拟活性污泥絮凝后的粒度分布。结果表明：与二元分布相比,该二项式分布可以得到更准确的粒度分布和平均粒度模拟值;通过校核二项式分布参数C_p的取值,可以提高粒度分布和平均粒度的模拟精度。相比于二元分布或正态分布只能描述一种类型的子粒子分布,该二项式分布具有较强的适应性,调整参数C_p的取值,可以得到更多可能的子粒子分布;参数C_p还可以表征粒子的破碎方式--较小的C_p值表征粒子具有较强的稳定性,易破碎生成较大的子粒子;较大的C_p值表征粒子具有较弱的稳定性,易破碎生成较小的子粒子。     

聚乙烯粉料粒径分布对熔体质量流动速率的影响

选择不同生产工艺的4种聚乙烯粉料，使用振筛机和不同孔径筛网进行筛分，得到不同粒径范围的聚乙烯粉料，用熔融指数仪测试这些粉料的熔体质量流动速率（MFR），考查不同粒径范围的聚乙烯粉料MFR的差异以及聚乙烯粉料粒径分布与MFR的关系，分析了聚乙烯粉料MFR测试结果的重复性与粉料粒度分布的关系，提出了在测试过程中如何正确操作减小MFR测试误差的方法，为粉料MFR的测定提供指导。结果表明，聚乙烯粉料的粒径分布对MFR有较大影响，通过测试前处理和规范称量时取样，可显著提高MFR测定结果的重复性。