Liquid Chromatographic Fractionations of Mixtures of Polystyrene Oligomers

Abstract

Oligomer mixtures of 800, 2200, and 4000 molecular weight polystyrene have been fractionated using silica and bonded phase columns under similar conditions of solvent gradient and flow rate. Using a hexane tetrahydrofuran gradient, the silica and nitro phases were best in that they separated 41 and 43 oligomers, respectively. At the other extreme, a phenyl bonded phase column gave virtually no resolution using a water/THF gradient, and a cyano bonded phase column, using the earlier hexane/tetrahydrofuran system, resolved only 10 oligomers. Amino and octadecyl bonded phase columns gave results intermediate between these two extremes. The strength of the solvent used to dissolve the sample was found to be of critical importance. Use of too good a sample solvent seriously degraded the attainable resolution. When number-average and weight-average molecular weights for an 800 molecular weight polystyrene sample were calculated from the oligomer distribution, the silica column gave values which were most consistent with those reported from other methods.     

Surface Area Study of Pretreated Silica Gels

Abstract

The surface areas of a series of pretreated silica gels were measured by a frontal-analysis chromatographic technique using benzene for which the cross-sectional area had been obtained by adsorption measurements on a sample of Sterling MT carbon black as a standard. Much smaller surface areas were found than when nitrogen was used. The chromatographic equilibrium constants for aromatic adsorbates, calculated using the surface areas measured with benzene, point to a change in the adsorption mechanism which was not apparent when nitrogen surface areas were used.     

硅灰和减缩剂对混凝土自收缩和孔隙的影响

硅灰和低水胶比会降低混凝土总孔隙率,但增加了混凝土自收缩,使其产生微裂纹。本文研究了掺入硅灰和减缩剂(SRA)对不同水胶比的混凝土自收缩和微观、宏观尺度孔径分布的影响。结果表明：掺入10%(体积分数)的硅灰会使混凝土自收缩增加27.3%～28.8%;而加入减缩剂使混凝土自收缩降低68.0%～85.1%,且对含有硅灰的混凝土样品降幅更大。此外,掺入硅灰和减缩剂可以使混凝土总孔隙率分别降低5.1%～6.0%和35.9%～39.7%,但硅灰会增大混凝土100 nm以下孔隙和100μm以上孔隙的体积占比,而减缩剂对这两类孔隙的体积则会起相反作用。同时,自收缩与100μm以上孔隙体积分数呈明显正相关关系。     

Synthesis of Si-N and B-N Preceramic Coatings on Silica Gel by Chemical Surface Coating: A Porosity Study

Silica gel has been modified by successive gas reactions with (SiCl₄-NH₃) and (BCl₃-NH₃) in order to obtain Si-N and B-N preceramic polymers, which are chemically bound to the substrate surface. The effect of the polymer synsthesis on the porosity characteristics of the substrate is determined as a function of the number of applied modification cycles, using N₂ adsorption-desorption isotherms recorded at 77 K. The elemental analysis data in combination with the adsorption isotherms yield a more detailed picture of the density and the homogeneity of the coatings. Using the pore size distributions, the contribution of pore blocking and pore narrowing can be calculated as a function of the amount of reaction cycles. A new calculation method for the pore blocking and pore narrowing, which is not based on any pore shape model, is also presented and compared with the former calculation method.     

Preparation and Characterization of Confined Atactic Polystyrene in Ordered Silica/Polystyrene Composites

Ordered silica/polystyrene composites were prepared via radical polymerization in silica colloidal crystal templates, and ordered macroporous polymers were accordingly obtained after removing the silica templates. The confinement effect of the templates on the polymers in the composites was investigated. NMR results indicated that the polystyrenes formed both inside and outside the template were atactic. The polystyrene inside the template possessed a higher molecular weight and a narrower molecular weight distribution than the bulk one outside the template. The glass transition temperature of the confined polystyrene increased significantly with decreasing silica sphere size of the templates, and so did the contraction of polymer pores. The smaller the silica sphere size of the templates, the more remarkable is the confinement, which could be explained by entropic confinement of the polymer chains within a fixed inorganic meso‐framework (T. P. Russell, Science 2001 , 293, 446).     

不同比表面积白炭黑并用对胶料性能的影响

研究不同比表面积白炭黑并用对胶料性能的影响。结果表明,在高填充白炭黑的配方体系中,通过低比表面积白炭黑与高比表面白炭黑的并用,胶料的硫化速率得到提升,胶料的Payne效应降低,白炭黑絮凝减少,轮胎滚动阻力降低,耐磨性能和抗切割性能提高。     

白炭黑比表面积对轮胎胎面胶性能的影响

研究不同比表面积的白炭黑对胎面胶性能的影响。结果表明:比表面积大的白炭黑1165MP胶料门尼粘度普遍较高,加工性能较差;比表面积大的白炭黑表面具有较多的羟基,缩短了焦烧时间,延长了硫化时间,降低了胶料的加工安全性;相对于比表面积较小的白炭黑1115MP胶料,白炭黑1165MP胶料的硬度、拉伸强度、拉断伸长率、撕裂强度和阿克隆磨耗量略有增大,其他性能接近。白炭黑1165MP的补强效果优于白炭黑1115MP。     

BET Sample Pretreatment of Synthetic Ferrihydrite and its Influence on the Determination of Surface Area and Porosity

Ferrihydrite is a poorly-ordered iron oxyhydroxide which possesses a high specific surface area (>200 m²/g). This makes it an important constituent for surface related processes in nature and catalysis. This study focuses on the precautions that have to be taken in the sample preparation prior to BET measurements in order to avoid essential structural transformations. The experiments showed that temperatures between 90 and 120°C are necessary to remove surface contaminations and simultaneously prevent structural transformation of the ferrihydrite during the outgassing procedure. Furthermore, care has to be taken to keep the humidity low in the immediate proximity of the sample, due to the strong impact of this parameter on the structural stability of ferrihydrite.     

相对压强对白炭黑氮吸附表面积测试稳定性的影响

研究相对压强对白炭黑氮吸附表面积测试稳定性的影响。结果表明:在相同液氮纯度、脱气温度、脱气时间、氮吸附点数量条件下,与相对压强范围为0.05~0.1时相比,相对压强范围为0.05~0.2时白炭黑的氮吸附表面积测量值偏低,且差值随氮吸附表面积的增大呈增大趋势;相对压强范围较小时,氮吸附表面积测试结果的线性相关因数较大,再现性较好,测试结果较稳定。     

Synthesis of High Surface Area Silica Gels Using Porous Carbon Matrices

Porous silica was prepared using the sol-gel synthesis with porous carbon matrices as a pore-forming support. Tetraethoxysilane (TEOS) was hydrolyzed in an acid medium in the presence of a substoichiometric amount of water. Various carbon materials were used, among them Sibunit and catalytic filamentous carbon. Carbon matrices were impregnated with hydrolyzed TEOS and dried, then carbon was removed by burning out in air at 873 K. The obtained porous silica samples were studied by adsorption and electron microscopic methods. The specific surface area as high as 1267 m²g and pore volume as high as 5.7 cm³/g were determined for some silica samples. Thus deposited SiO₂ was found to cover the carbon surface copying its surface. With CFC used as carbon matrix, silica nanotubes were obtained. Thermostability of such silica is significantly greater as compared to silica gels reported earlier.     

核-壳型聚苯乙烯/二氧化硅复合微球的制备

利用层层自组装的方法制备了粒径和组成可裁剪、具有核-壳式结构的单分散聚苯乙烯(PS)／二氧化硅(SiO2)复合微球．对复合微球进行热处理除去有机物中心，制备出壁厚可剪裁的空腔硅球，并对复合微球的热分解过程进行了研究．透射电镜(TEM)照片显示二氧化硅纳米颗粒在中心外生成均匀壳层，而煅烧后则可得到轮廓分明的球形空腔；比较PS，SiO2和复合球体及热处理后的粉体的红外光谱，可分别验证二氧化硅的成功组装和热处理过程中作为中心的PS的完全去除．在吸附相同层数的前提下，随着所选用的二氧化硅纳米粒子的粒径的增大(10-40nm)，复合微球的粒径增大，空腔球体的壁厚增加，中心粒子热分解的活化能增大．复合微球的热分解机理符合三维扩散机理．     

Preparation of Aluminum Hydroxide Gels by Precipitation: Effect of Proton Acceptors on Surface Area and Porosity

This work has been undertaken to study the effect of varying chain length of primary amines on the preparation of aluminum hydroxide gels by precipitation. The aluminum hydroxide gels have been prepared by precipitation from ethanolic solutions of AlCl₃.6H₂O adding primary amines (propylamine, octylamine, dodecylamine) which acted as proton acceptors during the hydrolysis reaction and made the precipitation possible. The prepared samples were freezedried and activated to temperatures of up to 773 K. This technique produced in general amorphous samples of high specific surface area (up to 570 m² g%^?1). The specific surface area measured by nitrogen adsorption and the pore size distribution determined by mercury porosimetry were differentiated according to the chain length of the amine used. These differences were further enhanced on thermal activation to the aforementioned temperatures.     

大孔容高比表面积硅胶的制备

采用硅酸钠和硫酸为原料,无水乙醇为交换剂,通过微波干燥制备大孔容高比表面积硅胶。研究了醇泡浴比、醇泡时间、微波干燥强度、微波干燥时间对硅胶孔径、孔容和比表面积的影响。研究结果表明,在醇泡浴比为2.5∶1.0,醇泡时间为30h,微波强度为550W,微波干燥时间为20min时可制备大孔容高比表面积的硅胶。     

碳化合成纳米SiO2颗粒比表面积的控制机理

以Na2SiO3为前驱物,研究了碳化合成纳米SiO2颗粒比表面积的控制机理. 正交实验结果表明,影响其比表面积的次序为Na2SiO3浓度>PEG6000添加量>反应温度>CO2/N2混合气流量. 当反应温度80℃、Na2SiO3浓度40 g/L、PEG6000 4 g/L、CO2/N2混合气流量1.2 L/min时,所制SiO2颗粒的比表面积为318.9 m2/g. 随Na2SiO3 浓度增大,SiO2胶粒在pH>7的碳化液中Ostwald凝聚生长过程相对延长,颗粒的一次粒径增大,比表面积却随之减小. 由于温度对SiO2溶解度和胶粒Brownian运动的影响,降低反应温度可促进SiO2成核、减少Si(OH)4和≡SiOSi(OH)3的聚合,SiO2颗粒的比表积增大. 添加剂PEG6000的空间架构效应抑制纳米SiO2颗粒团聚,从而促进SiO2颗粒比表面积增大;但当其浓度大于7 g/L时,Na2SiO3分子进入缠绕着的PEG长链架构内部,所得SiO2颗粒比表面积有所降低.     

Preparation of Copper Oxide with High Surface Area Associated with Mesoporous Silica

Copper oxide was synthesized by the one-pot synthesis methods associated with mesoporous silica in different synthetic conditions. The SBA route with Cu citrate sol was the most effective to prepare CuO with high surface area, where its crystallite size could be controlled with the pore size of the mesoporous structure. It also showed better catalytic activity for toluene oxidation.     

氧化硅片表面配基疏水性及含量对蛋白质吸附行为的影响

采用双偏振极化干涉分析技术研究了氧化硅片表面配基疏水性及含量对蛋白质质吸附行为的影响,用3种不同疏水性配基3-(氨丙基)三乙氧基硅烷(APTES)、3-(N-甲氨基丙基)三甲氧基硅烷(MAPTMS)和3-(N,N-二乙基氨丙基)三甲氧基硅烷(DAPTMS)修饰氧化硅片,通过修饰时间控制硅片表面配基含量,研究了配基疏水性对牛血清白蛋白质(BSA)的影响和配基含量(N含量)对BSA、细胞色素C和糜蛋白酶吸附行为的影响. 结果表明,BSA在疏水性最强的DAPTMS修饰的氧化硅表面吸附量及吸附动力学常数最大,分别为1.371 ng/mm2和0.056 s?1; DAPTMS含量对3种蛋白质吸附的影响与蛋白质疏水性密切相关,疏水性中等的BSA和细胞色素C为单分子层吸附,吸附量随N含量增加先增大后减小,N含量2.1%时吸附量最大,分别为16.9和60.2 nmol/m2. 疏水性较强的糜蛋白酶为多分子层吸附,吸附量随N含量增大而减小,N含量1.1%时吸附量及吸附动力学常数分别为78.6 nmol/m2和0.040 s?1.     

Influence of DCCAs on Optical Transmittance and Porosity Properties of TMOS Silica Aerogels

In the present paper, the experimental results on some physical properties of silica aerogels modified by four different drying control chemical additives (DCCAs): (i) oxalic acid (OXA), (ii) glycerol (GLY), (iii) N,N-dimethylformamide (DMF) and (iv) formamide (FA) are reported. The molar ratio of tetramethoxysilane (TMOS), methanol (MeOH), water (H2O) and ammonia (NH4OH) was fixed at 1 : 12 : 4 : 3.6 × 10–3 respectively, throughout our experiments, and the DCCA/TMOS molar ratio was varied accordingly. The DCCA/TMOS molar ratio at around 0.4 was found to be the limiting value for almost all the modified aerogels, above which the cracking probability of the aerogels increased drastically. Further, the DCCA modified aerogels were characterized by optical transmittance and porosity measurements. Physical properties such as bulk density, volume shrinkage and specific surface area were also determined for all the modified aerogels. The pore size distribution (PSD) was found to shift towards smaller pore radii for acidic (OXA) DCCA and larger pore radii for basic (FA, DMF) DCCAs. The results have been supported by particle and pore sizes observed using Scanning Electron Microscopy (SEM) and BET analysis.     

Nanonickel Particles Supported on Silica. Morphology Effects on Their Surface and Hydrogenating Properties

The combustion of light hydrocarbons finds an important application in volatile organic compounds (VOCs) abatement. Catalytic combustion is interesting in this domain, because it may be carried out at relatively low temperatures and under large air excess. For this purpose, precious metal-based catalysts are very performing, but the quest for a lower-cost alternative solution is necessary. In this field, conducting mixed oxides such as perovskites are good candidates, especially when they are electrochemically promoted. The present work shows that electrochemical promotion of catalytic activity (NEMCA effect) in propene total combustion can be carried out with La_0.8Sr_0.2Co_0.8Fe_0.2O₃, an electron-conducting perovskite-type oxide, deposited on YSZ.     

Monodisperse Porous Silica/Polymer Nanocomposite Microspheres with Tunable Silica Loading,Morphology and Porosity

Hybrid organic/inorganic nanocomposites combine the distinct properties of the organic polymer and the inorganic filler, resulting in overall improved system properties. Monodisperse porous hybrid beads consisting of tetraethylene pentamine functionalized poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) particles and silica nanoparticles (SNPs) were synthesized under Stoeber sol-gel process conditions. A wide range of hybrid organic/silica nanocomposite materials with different material properties was generated. The effects of n(H₂O)/n(TEOS) and c(NH₃) on the hybrid bead properties particle size, SiO₂ content, median pore size, specific surface area, pore volume and size of the SNPs were studied. Quantitative models with a high robustness and predictive power were established using a statistical and systematic approach based on response surface methodology. It was shown that the material properties depend in a complex way on the process factor settings and exhibit non-linear behaviors as well as partly synergistic interactions between the process factors. Thus, the silica content, median pore size, specific surface area, pore volume and size of the SNPs are non-linearly dependent on the water-to-precursor ratio. This is attributed to the effect of the water-to-precursor ratio on the hydrolysis and condensation rates of TEOS. A possible mechanism of SNP incorporation into the porous polymer network is discussed.     

Novel Hybrids of Polystyrene Nanoparticles and Silica Nanoparticles-Grafted-Graphite Via Modified Technique

We have designed polystyrene nanoparticles through modified nanoprecipitation cosolvent evaporation technique and conventional nanoprecipitation and solvent evaporation. Polystyrene nanoparticles were embedded with silica nanoparticles and graphite to analyze scope of nanoprecipitation cosolvent evaporation. Ultraviolet–visible spectroscopic revealed decreased band gap of polystyrene nanoparticles obtained via nanoprecipitation cosolvent evaporation. Scanning electron microscopic showed uniform morphology of polystyrene nanoparticles and polystyrene nanoparticles-based nanocomposites engendered by nanoprecipitation cosolvent evaporation. X-ray diffraction disclosed presence of crystalline domains due to silica nanoparticles content in amorphous structure. Glass transition temperature was increased from 94 (polystyrene) to 124°C (PSNPs/SiNPs 0.6) and 137°C (PSNPs/SiNPs/G 0.6) with filler loading. Electrical conductivity of PSNPs/SiNPs/G 0.6 was also found to be higher (1.53 S/cm).