Interactions Between an Ionic Liquid and Silica,Silica and Silica,and Rubber and Silica and Their Effects on the Properties of Styrene-Butadiene Rubber Composites

An investigation of the effect of an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMI), on the properties of silica reinforced styrene-butadiene rubber (SBR), aimed to correlate the interactions between the ionic liquid and silica, silica and silica, and silica and rubber with the macro-properties and microstructure of SBR and SBR/silica vulcanizates is described. The interaction between the ionic liquid and silica was characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), the interaction between silica and silica was characterized by a rubber processing analyzer (RPA), and the interaction between rubber and silica was characterized by the bound rubber content. The FTIR analysis revealed that BMI can react with the hydroxyl groups on the surface of silica, improving the compatibility between the rubber and silica. The RPA and bound rubber testing indicated that the interactions between silica and silica particles were weakened and the interaction between silica and rubber increased with the incorporation of BMI into the SBR rubber. The bound rubber content showed a maximum with a BMI content of 3 phr. At the same time, the dispersion of silica in SBR was improved with the incorporation of BMI. With the increase of BMI content, the curing rate was greatly improved and the crosslink density increased. BMI also increased the tensile strength and abrasion resistance of the SBR vulcanizates. Most important, the BMI significantly improved the dynamic properties of the rubber composites, especially the wet-skid resistance and rolling resistance. However, excessive BMI (beyond 3 phr) acted as a plasticizer and was detrimental to the mechanical properties, resulting in a decrease of tensile strength and abrasion resistance.     

Preparation and Properties of Polylactic Acid (PLA)/Silica Nanocomposites

Surface-modified silica was incorporated into bio-based polylactic acid (PLA) to improve its performance. The modification by aminosilane on the silica was confirmed through FTIR (Fourier transform infrared) spectra. Following the aminosilane modification, polyethylene glycol methyl ether (PEGME) was grafted, via the aminosilane, on the silica to form the desired surface-modified silica (PEGME-silica). The grafting percentage of polyethylene glycol methyl ether was about 6.9 wt%. Unmodified silica, having underwent a similar treatment to maintain the same thermal history but without adding silane and PEGME, was also prepared. The PEGME-silica system had slightly higher tensile strength than the unmodified silica system, with a rheological study showing an enhanced polymer matrix-dispersed silica interaction and better dispersion in morphology observations being proposed as the cause. The dynamic storage modulus in the terminal zone was reduced for large amounts of highly dispersed surface-modified silica in comparison with unmodified silica. Tan δ decreased significantly with increasing unmodified silica contents in the low frequency region, resulting in solid-like behaviors. On the other hand, there was only a limited decrement for modified silica-filled samples in the corresponding ranges, especially for low dosages of the modified silica. The shear thinning phenomenon appeared to be more pronounced for unmodified silica at high silica content, but not for modified silica. To the best of our knowledge, this is the first report of the effect of polyethylene glycol methyl ether (PEGME)-modified nanosilica on the properties of PLA/silica nanocomposites prepared under a melt mixing process to illustrate the significance of surface modification via Cole–Cole plots.     

Harvesting silica nanoparticles from rice husks

Biogenic silica nanoparticles were synthesized using rice husks (RHs) as the raw material via controlled pyrolysis. The characterization results showed that the morphology of the synthesized silica was highly related to the pretreatment of RHs and the pyrolysis conditions. Particularly, potassium cations in RHs were found to catalyze the melting of silica, during which the amorphous silica were converted to crystalline phase. Two hours of pyrolysis at 700 °C appeared to be ideal to synthesize silica nanoparticles with a diameter of ca. 20–30 nm. Higher temperature and longer duration of pyrolysis led to undesired melting of silica nanoparticles, while too low a temperature cannot effectively remove carbonous residues. Such amorphous silica nanoparticles with narrow size distribution and high purity are expected to replace silica gel and fumed silica for various applications.     

Photocatalytic characterization of silica coated titania nanoparticles with tunable coatings

Photocatalytic experiments were conducted using the silica coated titania nanoparticles with tunable coatings to photocatalytically degrade methyl orange in water solutions. When the silica loading on titania nanoparticles was 4.67 wt%, the silica coating layer was incomplete and the photocatalytic activity of coated nanoparticles was higher than titania nanoparticles. However, when the silica loading on titania nanoparticles increased to 9.33 wt%, the thickness of silica coatings was 1.5 nm and the photocatalytic activity of coated nanoparticles sharply decreased. When the silica loading on titania nanoparticles increased to 25.19 wt%, the coated nanoparticles still exhibited a certain photacatalytic activity due to the porosity of silica coatings. The change of the effective tiania surface area available for methyl orange caused by silica coatings and the dispersion stability were used to explain the difference in photocatalytic activity.This revised version was published online in August 2005 with a corrected issue number.     

Suspended bridge-like silica 2×2 beam splitter on silicon

We report a successful experimental realization of a 2×2 suspended silica splitter integrated on a silicon substrate. The silica splitter was photo-lithographically patterned, etched, and reflowed to form the suspended and rounded silica waveguide channels. The silica splitter showed a flat splitting ratio and excess loss over a wide wavelength range from 1520 to 1630 nm with a low crosstalk. Additionally, as a result of the very low nonlinear coefficients of silica, the splitting ratio is independent of input power.     

Subsurface defect characterization and laser-induced damage performance of fused silica optics polished with colloidal silica and ceria

This paper mainly focuses on the influence of colloidal silica polishing on the damage performance of fused silica optics. In this paper, nanometer sized colloidal silica and micron sized ceria are used to polish fused silica optics. The colloidal silica polished samples and ceria polished samples exhibit that the root-mean-squared(RMS) average surface roughness values are 0.7 nm and 1.0 nm, respectively. The subsurface defects and damage performance of the polished optics are analyzed and discussed. It is revealed that colloidal silica polishing will introduce much fewer absorptive contaminant elements and subsurface damages especially no trailing indentation fracture. The 355-nm laser damage test reveals that each of the fused silica samples polished with colloidal silica has a much higher damage threshold and lower damage density than ceria polished samples. Colloidal silica polishing is potential in manufacturing high power laser optics.     

Photocatalytic characterization of silica coated titania nanoparticles with tunable coatings

Photocatalytic experiments were conducted using the silica coated titania nanoparticles with tunable coatings to photocatalytically degrade methyl orange in water solutions. When the silica loading on titania nanoparticles was 4.67 wt%, the silica coating layer was incomplete and the photocatalytic activity of coated nanoparticles was higher than titania nanoparticles. However, when the silica loading on titania nanoparticles increased to 9.33 wt%, the thickness of silica coatings was 1.5 nm and the photocatalytic activity of coated nanoparticles sharply decreased. When the silica loading on titania nanoparticles increased to 25.19 wt%, the coated nanoparticles still exhibited a certain photacatalytic activity due to the porosity of silica coatings. The change of the effective tiania surface area available for methyl orange caused by silica coatings and the dispersion stability were used to explain the difference in photocatalytic activity.     

二氧化硅增透膜微观结构与激光损伤阈值的调控

采用溶胶-凝胶技术制备了二氧化硅增透膜,通过向溶胶中添加高分子聚乙烯醇缩丁醛（PVB）,调控胶体的粒径,进而控制膜层微观结构,研究膜层微观结构与激光损伤阈值的关系。纳米粒度仪和扫描探针显微镜测试表明:PVB加入溶胶后,控制了二氧化硅胶粒的生长,使二氧化硅胶粒生长更均匀,因而膜层的微观结构更均匀。当PVB质量分数为1%时,胶体粒径为15 nm,分散系数小于0.1。用该胶体镀膜,膜层均匀,表面粗糙度小于3.25 nm。并且PVB加入后增加了膜层胶粒间的黏附性,使得膜层强度增大。PVB加入使膜层的激光损伤阈值有所增加。当PVB的添加量为1%时,膜层的激光损失阈值从30.0 J/cm2增加到40.1 J/cm2。膜层激光损伤阈值的增加与膜层微观均匀性和物理强度的增加有关。     

The charging stability of different silica glasses studied by measuring the secondary electron emission yield

This paper reports that the charging properties of lead silica,Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission(SEE) yield.At a primary electron beam energy of 25 keV,the intrinsic SEE yields measured at very low injection dose are 0.54,0.29 and 0.35,respectively for lead silica,Suprasil and Infrasil silica glass.During the first e-beam irradiation at a high injection current density,the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state.At the steady state,the SEE yields of lead silica and Suprasil are 0.94 and 0.93,respectively.In Infrasil,several charging and discharging processes are observed during the experiment.This shows that Infrasil does not reach its steady state.Two hours later,all samples are irradiated again in the same place as the first irradiation at a low current density and low dose.The SEE yields of lead silica,Suprasil and Infrasil are 0.69,0.76 and 0.55,respectively.Twenty hours later,the values are 0.62,0.64 and 0.33,respectively,for lead silica,Suprasil and Infrasil.These results show that Infrasil has poor charging stability.Comparatively,the charging stability of lead silica is better,and Suprasil has the best characteristics.     

Superhydrophobicity of silica nanoparticles modified with polystyrene

Polystyrene/silica nanoparticles were prepared by radical polymerization of silica nanoparticles possessing vinyl groups and styrene with benzoyl peroxide. The resulting vinyl silica nanoparticles, polystyrene/silica nanoparticles were characterized by means of Fourier transformation infrared spectroscopy, scanning electron microscopy and UV-vis absorption spectroscopy. The results indicated that polystyrene had been successfully grafted onto vinyl silica nanoparticles via covalent bond. The morphological structure of polystyrene/silica nanoparticles film, investigated by scanning electron microscopy, showed a characteristic rough structure. Surface wetting properties of the polystyrene/silica nanoparticles film were evaluated by measuring water contact angle and the sliding angle using a contact angle goniometer, which were measured to be 159° and 2°, respectively. The excellent superhydrophobic property enlarges potential applications of the superhydrophobic surfaces.     

Properties and Preparation of Chitosan/Silanol Quaternary Ammonium Modified Silica Hybrids Using Sol–Gel Process

Chitosan/modified silica nanocomposites, with a sol–gel process being used to prepare a silanol quaternary ammonium modified silica possessing antimicrobial activity, were investigated, as well as the thermal properties, morphology, optical, mechanical, antimicrobial, and adsorption properties of this type of nanocomposite. Grafting of the modifier onto nanosilica was confirmed through the Fourier transform infrared (FTIR) spectra. X-ray diffraction patterns indicated that the chitosan structure was not disrupted from the incorporation of the modified silica. Fracture surfaces with no clear micro-phase separation were observed by scanning electron microscopy (SEM), which indicated the good interaction of chitosan and the modified silica. The organic modifier tended to cause the aggregation of the modified silica at higher content on a submicron scale based on transmission electron microscopy (TEM) analysis, which might be due to a decrease of the stability factor originating from the negative charges on silica. With the introduction of modified silica, the optical transmittance decreased at higher organic modifier content in agreement with TEM analysis. The elongation at break remained largely unchanged, but tensile strength and Young's moduli deteriorated in modified silica filled systems in comparison with pure silica filled systems. The introduction of the organic modified silica gave a higher antibacterial activity. All nanocomposites were capable of chelating Cu (II) as well as Fe (III) at a different degree. Thus, the prepared chitosan/modified silica nanocomposites exhibited both antimicrobial and chelating properties.     

Spatial and geometrical control of silicification using a patterned poly-l-lysine template

A simple process to achieve patterned silica films is described. The patterning of the catalyst poly-l-lysine via photolithography and liftoff enables the spatial and geometrical control of silicification. Microscopy and chemical characterization demonstrate that this process enables consistent patterning of silica with 10 μm resolution in a variety of geometries. In addition, the spatial and geometrical control of the silica is demonstrated under different reaction conditions and yields various silica morphologies. The ability to simultaneously pattern bio-inspired silica and control its morphology may allow the tailoring of silica and other silicon-based materials for future applications.     

The influence of filler modification on its aggregation and dispersion behaviour in silica/PBT composite

In this work, highly dispersed silica is obtained using a precipitation technique from emulsion medium. The selected emulsifier, applied in the process, allows production of silica with almost ideally spherical particles. To examine the tendency to aggregation, the silica powder is treated with commercially available silane coupling agents: 3-mercaptopropyltrimethoxysilane (A-189), N-2-(aminoethyl)-3-aminopropyltrimethoxy silane (A-1120) and 3-methacryloxypropyltrimethoxysilane (A-174). The silica microstructure is characterised by scanning electron microscopy (SEM). Size distribution of primary particles, aggregates and agglomerates structures is determined using dynamic light scattering (DLS) method. Surface treatment of silica generally enhances powder dispersibility. The pristine spherical silica and silica modified with silanes are introduced to poly(butylene terphthalate) (PBT). Dispersion of nanosize precipitated silica particles in PBT matrix is studied by SEM technique. For the visualisation of silica particles covered by polymer layer, the composite fracture surfaces are etched by air-plasma. The agglomerates of untreated silica are not efficiently destroyed during the extrusion process, whereas surface treatment by selected silanes leads to a significant reduction of agglomerate number. However, a large number of small, strongly bonded aggregates still occupied the composite structure.     

Silica-covered Au nanoresonators for fluorescence modulating of a graphene quantum dot

We synthesize Au@SiO2composite particles with a core-shell structure, and utilize the Au@SiO2nanoparticles to modulate the fluorescence emission of the graphene quantum dot(GQD) through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.     

Magnetic nanocomposite spinel and FeCo core-shell and mesoporous systems

The fabrication of condensed silica and mesoporous silica coated spinel CoFe₂O₄ and FeCo alloy magnetic nanocomposites are reported. The encapsulation of well-defined 5 nm thick uniform silica layer on CoFe₂O₄ magnetic nanoparticles was performed. The formation of mesopores in the shell was a consequence of removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the mesoporous silica. The mesoporous silica shells leads to a larger coercivity than that of pure CoFe₂O₄ magnetic nanoparticles due to the decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated by condensed and mesoporous silica. The condensed silica can protect the reactive FeCo alloy from oxidation up to 300 °C. However, saturation magnetization of FeCo nanoparticles coated by silica after 400 °C annealing is dramatically decreased due to the oxidation of the FeCo core. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product could be used in the field of biomedical applications.     

PMMA/凝胶玻璃复合材料作为非线性有机分子掺杂基质的研究

对分散红1（DR1）掺杂聚甲基丙烯酸甲酯（PMMA）／凝胶玻璃复合材料的光学二阶非线笥及其热稳定性进行了研究。结果表明,PMMA／凝胶玻璃作为一种有机／无机复合材料,是介于胶玻璃和PMMA之间的一种非线性有机分子掺杂基质。随复合材料中凝胶玻璃含量增多,所制备的非线性材料的热稳定性能变好。对非线性和热稳定性的折衷考虑,获得了制备光学二阶非线笥基质材料先体PMMA和正硅酸乙酯（TEOS）的最佳混合比例。     

Formation of hook-shaped and straight silica wires by a thermal vapor method

Hook-shaped and straight silica wires have been successfully synthesized on silicon wafer through a simple thermal vapor method with or without assistance of Al, respectively. The hook-shaped silica wires have amorphous structures with nearly 100 μm long and about 4 μm in average diameters, while the straight silica wires are hundreds of micrometers long and approximately 50–300 nm in diameters. The composition analysis revealed that larger Al/SiO_x islands can form on the silicon substrate with Al catalysts, whereas tiny silica clusters form without Al catalysts. They could act as the nucleation centers for the growth of silica wires with different shapes. The formation process of hook-shaped silica microwire results from a thermal gradient on the silicon substrate. The thermal gradient may be caused by the cold gas flowing during the process or other factors that lead to uneven temperature. On the contrary, straight growth of silica submicrowire is unacted on the thermal gradient factor due to the tiny silica clusters as nucleation centers. The present simple and low-cost process of producing hook-shaped and straight silica wires in bulk may lead to potential applications in catalysts, electrode materials, biosensing, etc.     

Non-Isothermal Crystallization Kinetics of Poly(Butylene Terephthalate)/Silica Nanocomposites

Poly(butylene terephthalate)/silica nanocomposites were prepared by in situ polymerization of terephthalic acid, 1,4-butanediol and silica. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of silica in the PBT matrix. The non-isothermal crystallization behavior of pure PBT and its nanocomposites was studied by differential scanning calorimetry (DSC). The results show that the crystallization peak temperatures of PBT/silica nanocomposites are higher than that of pure PBT at a given cooling rate. The values of halftime of crystallization indicate that silica could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization. The non-isothermal crystallization data were analyzed with the Avrami, Ozawa, and Mo et al. models. The non-isothermal crystallization process of pure PBT and PBT/silica nanocomposites can be best described by the model developed by Mo et al. According to the Kissinger equation, the activation energies were found to be ?217.1, ?226.4, ?259.2, and ?260.2 kJ/mol for pure PBT and PBT/silica nanocomposites with silica weight content of 1, 3 and 5 wt%, respectively.     

Synthesis of nanostructured polymer materials with different morphologies: Nanoporous ordered networks and hollow capsules

Nanostructured polymer materials with interesting morphological variation, which include three dimensionally interconnected uniform nanoporous network arrays (volume- and surface-templated ordered arrays) and hollow core spheres were synthesized by inducing different polymerization process of phenol and formaldehyde as a precursor over silica templates (ordered silica colloidal crystals or individual silica particles). The pore sizes of the resulting nanostructured polymer materials can be easily controlled by monitoring the sizes of silica spheres, while their morphologies were modulated by controlling the initiation sites of the acid-catalyzed condensation reaction of the same polymer precursor and by modifying silica templates.     

Applied electric field to fabricate colloidal crystals with the photonic band-gap in communication waveband

The macropore silica colloidal crystal templates were assembled orderly in a capillary glass tube by an applied electric field method to control silica deposition. In order to achieve the photonic band gap (PBG) of colloidal crystal in optical communication waveband, the diameter of silica microspheres is selected by Bragg diffraction formula. An experiment was designed to test the bandgap of the silica crystal templates. This paper discusses the formation process and the close-packed fashion of the silica colloidal crystal templates was discussed. The surface morphology of the templates was also analyzed. The results showed that the close-packed fashion of silica array templates was face-centered cubic (FCC) structure. The agreement is very good between the experimental data and the theoretical calculation.