Preparation of SiO2/PMMA composite particles via conventional emulsion polymerization

A series of SiO₂/PMMA composite particles with different morphologies were prepared by conventional emulsion polymerization by the aid of acid–base interaction between the silanol groups of unmodified silica particles and the amino groups of 4‐vinylpyridine. In this approach, no surface treatment for nanosilica particles was required. The morphologies of composite particles, for example, multicore–shell, raspberry‐like, and conventional core–shell, could be controlled by modulating emulsifier content, monomer/silica ratio, silica size, and monomer feed method. The possible particle formation mechanisms were discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3807–3816, 2006     

Formation of an in situ nanosilica nanomatrix via graft copolymerization of vinyltriethoxysilane onto natural rubber

Natural rubber (NR) with an in situ nanosilica nanomatrix was characterized in present work. The in situ nanosilica nanomatrix was prepared via graft copolymerization of a silane monomer, vinyltriethoxysilane (VTES), onto deproteinized NR (DPNR) in latex stage using tetrapentamine (TEPA)/tert‐butylhydroperoxide (TBHPO) as initiators. VTES conversion of more than 80% was obtained, and it depended on VTES concentration. The graft copolymer structure was characterized by Fourier transform infrared (FT‐IR), solution‐state proton nuclear magnetic resonance (¹H‐NMR), and solid‐state ²⁹Si‐NMR spectroscopy. FT‐IR analysis of the graft copolymer confirmed the formation of in situ silica particles, while solution‐state ¹H‐NMR and solid‐state ²⁹Si‐NMR revealed the partial hydrolysis of the ethoxy groups and polycondensation of the silanol groups. The formation of nanosilica particles enhanced thermal and mechanical properties of the graft copolymer. Morphology observations of the in situ nanosilica nanomatrix through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the spherical nanosilica particles form a nanomatrix surrounding NR particle. The formation of the nanomatrix was proved to enhance mechanical properties for NR materials.     

Adsorption equilibriums in a silica-poly(vinyl alcohol)-gelatin system

The interaction of gelatin with nonporous nanosized amorphous silica containing poly(vinyl alcohol) (PVA) preliminarily adsorbed on its surface is studied. It is established that the modification of the nanosilica via PVA adsorption does not influence its ability to adsorb the protein. It is shown that, during adsorption, gelatin partly displaces PVA molecules from the silica surface. It is assumed that hydroxyl groups of strongly retained PVA macromolecules may play the role of active sites of protein adsorption along with free silanol groups.     

Correlating the Morphological Properties and Structural Organization of Monodisperse Spherical Silica Nanoparticles Grown on a Commercial Silica Surface

A variety of nanosilicas have been widely used to fabricate rough surfaces with superhydrophobic and superhydrophilic properties. In this context, we prepared mixed silica and mixed nanosilica that were generated by the growth and self‐assembly of synthesized monodisperse silica nanospheres (11–30 nm, 363 m² g^?1) on the surface of Sylopol‐948 and Dispercoll S3030 by using a base‐catalyzed sol–gel route. Using this process, the interactions and hierarchical structure between the nano‐ and microsized synthesized silica particles were studied by changing the amount of tetraethoxysilane. The resulting materials were characterized by BET analysis, small‐angle X‐ray scattering (SAXS), dynamic light scattering, FTIR spectroscopy, and SEM. The mixed silica presented a higher specific surface area (326 m² g^?1), a six‐fold higher percentage of (SiO)₆ (44–68 %), and a higher amount of silanol groups (14.0–30.7 %) than Sylopol‐948 (271 m² g^?1, 42.6 %, and 12.5 %, respectively). The morphological and hierarchical structural differences in the silica nanoparticles synthesized on the surface of commercial silica (micrometric or nanometric) were identified by SAXS. Mixed micrometric silica exhibited a higher degree of structural organization between particles than mixed nanosilica.     

Physical and optical properties of organo-modified silica nanoparticles prepared by sol–gel

A comparative study on the physical and optical properties of silica nanoparticles prepared by sol–gel has been carried out. Post-modification of as-synthesized silica nanoparticles produced organo-functionalized silica nanoparticles slightly increased in size (~20%) and relatively high aggregation. However, in situ method produced sixfold bigger functionalized particles with good dispersion and less aggregation. Higher organic content was observed for in situ modified nanosilica, leading to a higher surface hydrophobicity that improved compatibility and dispersion in preparation of silica-polymer nanocomposite. Furthermore, in situ and post-modified nanosilica demonstrated a distinct optical activity, photoluminescence and UV compared to the unmodified nanoparticles.     

原位聚合法制备纳米二氧化硅/聚氨酯复合树脂

采用高压剪切分散（HPSH）的方法先将纳米SiO2分散在合成聚氨酯原料中,再应用原位聚合的方法制备了纳米SiO2/聚氨酯复合树脂。 用热重分析、动态机械热分析（DMTA）和扫描电子显微镜等测试技术研究了纳米SiO2的用量及其分散方法对聚氨酯树脂的热稳定和力学性能的影响。 结果表明,二苯甲基二异氰酸酯（MDI）中的-NCO和纳米SiO2表面的-OH发生了化学反应,SiO2表面的包覆率约为7%;通过高压剪切分散的方法能够使纳米SiO2在聚氨酯基体中均匀的分散开来,粒径为30~40 nm,而超声处理的纳米SiO2会聚集约为200 nm聚集体。 当SiO2的添加质量分数为3%时复合树脂（HPSH处理SiO2）的拉伸强度和断裂伸长率均达到最大值,分别为84.3 MPa和438.7%。 此外,与纯树脂相比,复合树脂(4%纳米SiO2)的Tg、Td和T-50%分别增加了17.2、9和21 ℃。     

Tris(2-methyl-8-quinolinolato)iron(III) as a novel spectrophotometric probe for silanol detection.

Tris(2-methyl-8-quinolinolato)iron(III) was proposed as a sensitive spectrophotometric silanol-detecting probe based on the coordination ability of silanol groups on the surface of octadecylsylanized silica gel (ODS silica gel) for reversed-phase high-performance liquid chromatography. A peak of the iron(III) complex on a chromatogram abruptly collapsed as the silanol content in an ODS column increased, indicating that the iron(III) complex could sense trace amounts of silanol groups. The change of the peak parameters, such as the peak height and the peak area was highly related to the output of some nitrogen-containing compounds used as silanol-detecting probes as a function of the silanol content in an ODS column. The response of the peak height of the iron(III) complex to the silanol content was much more sensitive than the response of the nitrogen-containing probes, and was comparable to that of tris(2-methyl-8-quinolinolato)gallium(III), which had been proposed as a fluorometric silanol-detecting probe based on the coordination ability of the silanol groups.     

Electron spin resonance studies of spin-labelled polymers—18: Adsorption of spin-labelled poly(vinyl acetate) on silica surfaces

The adsorption of spin-labelled poly(vinyl acetate) from dilute solutions in ethyl acetate, chloroform and toluene onto three silica adsorbents of different surface silanol contents was studied. The adsorption capacities of the three silica samples, which decreased with decreasing surface silanol content, were dependent on the nature of the solvent, being greatest in the poor solvent toluene and least in the good solvent ethyl acetate. The ESR spectra of the polymer adsorbed on the silica of highest silanol content suggested that the polymer had a relatively flat conformation when toluene or chloroform was solvent and a more looped conformation when ethyl acetate was solvent. With the silica of intermediate silanol content, the polymer adsorbed from chloroform solution also had a loopy conformation. The silica of lowest silanol content was prepared by treating the first silica absorbent with trimethylchlorosilane. The line-shapes in the ESR spectrum of the labelled polymer adsorbed on this modified silica indicated a change in mode of adsorption.     

Surface and interface characterization of polyester‐based polyurethane/nano‐silica composites

Polyester‐based polyurethane/nanosilica composites were prepared via in situ polymerization and investigated by contact angle measurement, transmission electron microscopy (TEM), atomic force microscopy (AFM) and peel testing in an Instron testing machine. The contact angle and surface free energy results show that nanosilica tended to enrich at the interface between nanocomposite polymers and the substrates, TEM indicated that nanosilica particles were evenly dispersed in the bulk and AFM demonstrated that nanoparticles were located at both the surfaces and interfaces of nanocomposite polymers and that the roughness of both the surfaces and interfaces had a decreasing tendency as the nanosilica content increased, as did the adhesion strength between the nanocomposite polymers and substrates. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermal pretreatment of silica composite filler materials

Three different silica filler materials were thermally treated in order to effect dehydration, dehydroxylation, and rehydroxylation. Samples were characterized by thermogravimetry (TG), pycnometry, elemental analysis, and scanning electron microscopy (SEM). For all fillers, our results indicate incremental removal of silanol groups at higher heating temperatures and irreversible dehydroxylation at over 673 K. To remove the organic content and maintain adequate silanol density for subsequent silanization on Stöber-type silica, we suggest heating at 673 K followed by overnight boiling in water.     

Polar contributions of the stationary phase to the reversed-phase ion-pair high-performance liquid chromatographic separation of quaternary ammonium drugs

The chromatographic reproducibility of a methodology, developed for the separation and determination of quaternary ammonium drugs by reversed-phase ion-pair column liquid chromatography, was studied. The results in terms of retention dependence on the residual silanol content of the octadecyl stationary phase and column aging were compared with those obtained with conventional separation techniques. By on-column silylation with N-trimethylsilylimidazole, it was demonstrated that eluents containing both amines and alkanesulphonates, beside a higher resolving power, provide reproducible separations which are far less dependent on the residual and generated silanol groups compared to those obtained with eluents containing only an organic amine.     

Influence of the Curing Temperature in the Mechanical and Thermal Properties of Nanosilica Filled Epoxy Resin Coating

0.5–3 wt% nanosilica was added to an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) and cured at 25, 40 or 60 °C using isophoronediamine (IPDA) as hardener. Aggregates of nanosilica were properly dispersed into the DGEBA-IPDA resin and agglomerates formation was avoided. Addition of nanosilica increased the storage modulus E′ and the area and height of the tan δ curve of DGEBA-IPDA resin cured at 25 °C, but no significant differences were found by curing at higher temperature. Gel time measurements and the results obtained by applying the Kamal model to isotherm DSC curing of DGEBA-IPDA-nanosilica revealed that nanosilica catalysed the curing reaction between DGEBA and IPDA, in less extent by increasing the curing temperature.     

Highly toughened poly(lactic acid) (PLA) prepared through melt blending with ethylene-co-vinyl acetate (EVA) copolymer and simultaneous addition of hydrophilic silica nanoparticles and block copolymer compatibilizer

In this study, a highly toughened PLA was prepared through physical melt-blending with EVA at the presence of hydrophilic nanosilica and SEBS-g-MA block copolymer compatibilizer. The effect of nanosilica and compatibilizer on the morphology, mechanical properties, and linear rheology of the PLA/EVA blends was also investigated. According to TEM images, nanosilica was selectively located in the PLA matrix while some were placed on the interface between the two polymers as was also predicted by thermodynamic and kinetic analysis. Upon the addition of nanoparticles, the interfacial adhesion between the phases was enhanced and the average droplet size decreased. Interestingly, incorporation of SEBS-g-MA induced morphological changes as the spherical EVA droplets turned into a cylindrical shape. DSC results indicated that blending with EVA copolymer resulted in the reduction of crystallization of PLA matrix; however, the crystallinity increased at the presence of nanoparticles up to 5 wt%. The addition of compatibilizer considerably hindered the crystallization of the PLA phase. PLA/EVA blend containing optimum levels of nanosilica exhibited considerably enhanced tensile toughness, elongation at break, and impact strength. On the other hand, the simultaneous addition of nanoparticles and SEBS-g-MA led to synergistic toughening effects and the compatibilized blend containing nanosilica exhibited excellent impact toughness. For instance, the elongation at break of the compatibilized PLA/EVA blend containing the optimal content of nanosilica was increased from 7% to 121% (compared to neat sample). The notched Izod impact strength was also increased from 5.1 to 65 kJ/m². Finally, the microstructure of the blends was assessed by rheological measurements.     

化学反应-顶空气相色谱法测定气相二氧化硅表面硅羟基

建立了一种基于化学反应-顶空气相色谱测定气相二氧化硅表面硅羟基含量的新方法。实验取气相二氧化硅放入顶空瓶中于105 ℃烘箱中加热2 h去除水分,将甲苯稀释的格氏试剂注入密闭的顶空瓶中,格氏试剂与气相二氧化硅表面硅羟基快速反应产生甲烷(CH₄),甲烷量与气相二氧化硅表面硅羟基含量成正比。经过气相色谱-氢火焰离子化检测器测定甲烷,通过外标法定量,根据化学反应方程式计算出样品中羟基含量。同时对反应溶液用量与反应时间等条件进行优化,确定2.0 mL反应溶液,反应15 min为最优的前处理条件。结果表明,硅羟基含量与气相色谱信号值之间存在良好的线性相关性,相关系数为0.9990,相对标准偏差小于3%,本方法的检出限为0.30 mg/g,定量限为1.00 mg/g,开展了4家实验室对5个不同比表面积的样品测试,数据结果的重复性限(r)小于2.5%,再现性限(R)小于6.5%。该方法结合自动化技术,顶空反应操作简单,样品量和试剂用量少,准确性高,重复性好,优于酸碱滴定法,适用于快速检测气相二氧化硅表面硅羟基的含量,解决了硅羟基利用传统方法难以准确测定的难题。该方法的建立对我国二氧化硅产业硅羟基检测标准的制定和产业技术优化,均具有重要的理论和现实意义。     

Classification of reversed-phase materials by means of selected chromatographic data

Summary Using n-heptane as eluent a direct linear correlation was found between the logk’ values of various polar test compounds and the silanol content determined by the methyllithium method. The peak asymmetries pass through a maximum at a medium silanol content. Peak asymmetries and logk’ values depend also on the chain length of the bonded alkyl group. A computer program was used to classify 25 home-made RP materials, 7 commercial products and the starting silica to achieve a hierarchical classification of them. The arrangement provides some detailed information about the presence and the effect of silanol groups. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

A Study on the Surface Silanol Groups Developed by Hydrothermal and Acid Treatment of Faujasite Type Zeolites

The surface silanol groups on faujasite type zeolites, which were formed by hydrothermal and acid treatments and considered to be lattice defect, were characterized. IR measurements of silanol groups were made in situ and thermogravimetic analysis was conducted under vacuum so as to quantify their content. It was thus possible to quantify separately the concentration of silanol groups forming hydroxy nests and the concentration of terminal silanol groups present on the secondary pores and crystal external surfaces. As the evacuation temperature increased, silanol groups forming hydroxy nests were found to decrease as a result of dehydroxylation condensation. The number of terminal silanol groups on the secondary pores and external surface remained virtually unchanged. The concentration of terminal silanol groups agreed well with the value calculated according to the proposed destruction model of the zeolite framework. This justified the model that there remained the double 6-ring structure on the secondary pore surfaces after the sodalite cage was collapsed as a result of the treatments. The effect of silanol groups forming hydroxy nests on the zeolite surface polarity was examined by measuring immersional heats in various solvents. It turned out that the extremely localized silanol groups forming hydroxy nests in the framework were linked via hydrogen bond to each other and showed nonpolar behavior. Copyright 1999 Academic Press.     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

Synthesis and characterization of high surface area nanosilica from rice husk ash by surfactant-free sol–gel method

A nanosilica powder was obtained by thermal treatment of rice husk ash using the sol–gel method without adding any extra surfactant, and was characterized by several techniques. Fourier transform infrared measurements revealed the similarity of the absorption curves of both standard nanosilica and synthesized nanosilica. From the nitrogen adsorption–desorption analysis followed that the nanosilica showed very high surface area of 653 m²/g, total pore volume of 0.64647 mL/g, and narrow pore radius of about 1.98 nm. Scanning electron microscopy of the nanosilica sample dried at 120 °C showed separated particles, while the particles of the sample sintered at 700 °C were aggregated. The analysis of transmission electron microscopy (TEM) micrographs and showed that about 69 % of particles had their sizes in the range of 20–25 nm. X-ray diffraction measurements showed the amorphous nature of the synthesized silica. Applying the Debye–Scherrer formula provided the value of the mean crystallite size around 26 nm which agreed with the one determined from TEM. The purity of the prepared nanosilica was higher than 95 % silica which was confirmed by means of energy dispersive X-ray analysis.     

Synthesis and Characterization of Polystyrene/Nanosilica Organic-Inorganic Hybrid

IntroductionIn the past two decades, because of its potentialindustrial applications, organic-inorganic compositeshave attracted the attention of both researchers andacademicians. Organic-inorganic hybrids offer the pos-sibility to combine both the advant…     

Accessible silanol sites - beneficial for the RP-HPLC separation of constitutional and diastereomeric azaspirovesamicol isomers

Different RP-HPLC columns (phenyl, conventional ODS, cross-linked C(18) and special end-capped C(8) and C(18) phases) were used to investigate the separation of four basic ionizable isomers. Using ACN/20mM NH(4)OAc aq., a separation was observed exclusively on RP columns with higher silanol activity at unusual high ACN concentration, indicating cation-exchange as main retention mechanism. Using MeOH/20mM NH(4)OAc aq., another separation at low MeOH concentrations was observed on both, RP columns with higher as well as RP columns with lower silanol activity, which is mainly based on hydrophobic interactions. The isomers were also separated on a bare silica column at higher MeOH content using NH(4)OAc. Since cation-exchange governs this retention, the elution order was different compared to the RP phases. A strong retention on the silica column was observed in ACN, which could be attributed to partition processes as additional retention mechanism.