Surface modification of cellulose nanocrystals

In order to improve the dispersibility of cellulose nanocrystal (CNC) particles, three different grafted reactions of acetylation, hydroxyethylation and hydroxypropylation were introduced to modify the CNC surface. The main advantages of these methods were the simple and easily controlled reaction conditions, and the dispersibility of the resulting products was distinctly improved. The properties of the modified CNC were characterized by means of Fourier transform infrared spectroscopy (FT-IR), ¹³C nuclear magnetic resonance (NMR), transmission electron microscopy (TEM) and thermogravimetric analyses (TGA). The results indicated that after desiccation, the modification products could be dispersed again in the proper solvents by ultrasonic treatments, and the diameter of their particles had no obvious changes. However, their thermal degradation behaviors were quite different. The initial decomposition temperature of the modified products via hydroxyethylation or hydroxypropylation was lower than that of modified products via acetylation. Translated from Acta Polymerica Sinica, 2006, (8): 982–987 [译自: 高分子学报]     

Stabilization of cubic phase in scandium-doped zirconia nanocrystals synthesized with sol-gel method

A new room-temperature synthesis of nanocrystals of scandium-doped zirconium oxide by sol-gel method is reported. The structure of the obtained product is checked with standard structural analysis methods. The crystal phase of ZrO₂-Sc₂O₃ nanocrystals changes from monoclinic to tetragonal and cubic with the increase in scandium concentration. The importance of the cubic phase, which appears at 10 mol% and refines at 16 mol% of Sc₂O₃ concentration, is emphasized. The UV-Vis absorption spectra of the product are measured, and its bandgap is evaluated from the fundamental absorption edge. The value of the bandgap was calculated as 5.65 eV for the cubic phase.     

Processing and properties of polycrystalline cubic boron nitride reinforced by SiC whiskers

Dense polycrystalline cBN (PcBN)–SiCw composites were fabricated by a two-step method: First, SiO₂ was coated on the surface of cubic boron nitride (cBN) particles by the sol-gel method. Then, silicon carbide whisker (SiC_w)- coated cBN powder was prepared by carbon thermal reaction between SiO₂ and carbon powders at 1500°C for 2 hour. Then, cBN–SiC_w complex powders were sintered by high-pressure and high-temperature sintering technology using Al, B, and C as sintering additives. The phase compositions and microstructures of cBN–SiC_w composites were investigated by X-ray diffraction and scanning electron microscopy, respectively. It was found that the SiC_w and Al₃BC₃ had been fabricated by in situ reaction, which cannot only promote densification but also improve mechanical properties. The relative density of PcBN composites increased from 96.3% to 99.4% with increasing SiC_w contents from 5 to 20 wt%. Meanwhile, the Vickers hardness, fracture toughness and flexural strength of as-obtained composites exhibited a similar trend as that of relative density. The composite contained 20 wt% of SiC_w exhibited the highest Vickers hardness and fracture toughness of 42.7 ± 1.9 GPa and 6.52 ± 0.21 MPa•m^1/2, respectively. At the same time, the flexural strength reached 406 ± 21 MPa.     

聚甲基丙烯酸甲酯对碳化硅表面改性的研究

制备了低分子量的聚甲基丙烯酸甲酯,用其对碳化硅粉进行表面处理。改善了粉体的流动性,为制备高固相含量浆料奠定了基础。     

Ozonide ions on the surface of MgO nanocrystals

The adsorption properties of oxygen radicals on the surface of polycrystalline oxides can provide relevant information about the functionality of specific surface sites in oxidation catalysis. Using electron paramagnetic resonance spectroscopy, we investigated O₂ adsorption at MgO nanocrystal surfaces which were previously enriched with O⁻ radicals i.e. trapped hole centers. On dehydroxylated particle surfaces, two ozonide radical types O ₃ ⁻ were isolated as adsorbates and the related energies for O₂ adsorption were found to be 55 ± 5 kJ mol⁻¹ and 100 ± 5 kJ mol⁻¹. The respective adsorption sites are assigned to hole centers trapped on oxygen terminated corners and cation vancancies, respectively. In addition, O ₃ ⁻ ions were also employed as probes for electron trapping sites on partially hydroxylated sample surfaces. Five types of O⁻ radicals emerge from surface colour centre bleaching with N₂O, but only two of them adsorb O₂ at room temperature. A connection between the well-characterized (H⁺)(e^-) defect – an electron trapped in close vicinity of a nearby proton [Chiesa et al. J. Phys. Chem. B 109 (2005) 7314] – and one ozonide type which exhibits significant magnetic coupling with an adjacent proton, was established on the basis of their production parameter dependence. Although the g tensor of an O₃ ⁻ species reflects the properties of the radical itself rather than the structure of the adsorption site, the related signatures are proposed to serve also as spectroscopic fingerprints for catalytically relevant surface anion environments.     

纳米碳化硅的表面改性和分散性研究

采用氢氟酸对原始纳米SiC颗粒进行表面改性,以制备稳定分散的纳米SiC浆料。借助XRD、比表面仪、FT-IR和扫描电子显微镜等对改性前后纳米SiC颗粒进行了表征,发现SiC颗粒表面的Si—O键消失,表明表面的SiO2薄层被去除了,颗粒之间无明显团聚现象。根据比表面积结果,确定改性时间为15 min最好。借助分光光度法,对不同分散剂和超声时间进行研究,确定乙醇为分散剂,超声时间为5 min时,纳米SiC浆料具有较强的分散稳定性。     

Surface modification of cellulose nanocrystals towards new materials development

Cellulose nanocrystals (CNCs) are a kind of sustainable nanoparticle from biomass, which are widely used as reinforcing filler and assembly building block for high-performance composites and function materials including biomaterial, optics, and so forth. Here, their unique advantages in material applications were reviewed based on their rod-like morphology, crystalline structure, dimension-related effects, and multi-level order structure. Then, we focused on the molecular engineering of CNCs, including the structure and physicochemical properties of their surface, along with surface modification methods and steric effects. We further discussed the performance-improvement and functionalization methods based on multi-component complex systems, together with the effects of surface molecular engineering on the performance and functions. Meanwhile, methods of optimizing orientation in uniaxial arrays were discussed along with those of enhancing photoluminescence efficiency via surface chemical modification and substance coordination. In the end, we prospected the design, development, and construction methods of new CNCs materials.     

SiC反射镜表面改性研究进展

采用SiC陶瓷作反射镜是目前国际上的一个研究热点。但是SiC陶瓷用作反射镜时存在各种类型的缺点,必须对SiC反射镜表面进行改性。本文综述了各种表面改性方法、制备机理以及优缺点,最后展望了未来SiC反射镜的发展方向：即低成本化和大型化。     

Photochemical Etching of Silicon

Silicon that was immersed in hydrofluoric acid can be etched photochemically by laser, and it was found to produce long and regular columnar structure, if the laser power density is greater than 10 mW/mm². Another criterion is that the laser wavelength should be at the blue end of visible spectrum. Fine wires with diameter 300–200 nm were also observed at the top of these columns. The dimension of these fine wires is near to quantum confinement dimension, thus can be taken as supporting evidence for quantum confinement. The photoluminescence spectra full width half maximum was narrower than that from porous silicon fabricated from conventional anodisation method. The narrower full width was attributed to the uniformity of the porous silicon structure. A physical model is proposed to explain the observed strong directional etching. The model showed that once the etch sites have randomly initiated, the etching rate becomes directional under the influence of laser. The intensity of laser controls the etching direction such that silicon columns are formed if the intensity of the laser is strong enough.     

Emulsifier-free emulsion copolymerization of styrene with two different amino-containing monomers: II. Surface and colloidal characterization

The colloidal and surface properties of copolymer latex particles prepared by batch emulsifier-free emulsion polymerization of styrene with two different amino-containing monomers (Amino Ethyl Methacrylate Hydrochloride (AEMH) and Vinyl Benzyl Amine Hydrochloride (VBAH)), and 2,2′-azobis(2-amidinopropane) dihydrochloride (V50) as initiator were investigated. The final particle size was found to decrease with increasing the functional monomer concentration. Different titration methods were used to quantify the surface amino (brought by the monomer) and amidino groups (originated from the initiator) on the latex particles. The same behavior was observed on both type of latexes: increasing the functional monomer concentration caused the surface amino groups density to increase from 0 to a plateau value at 8.2 μC/cm², whereas the surface amidino groups density decreased from 18.5 to 2 μC/cm². These results were confirmed by electrophoretic measurements and they corroborated those obtained in a previous kinetic study (Part 1) concerning the role of functional monomers as transfer agents. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2331–2342, 1997     

表面修饰CdTe量子点的合成及其光学特性

在水相中合成高发光性能的CdTe量子点,研究以巯基乙酸(TGA)为稳定剂对CdTe表面进行修饰,制备在水中分散性良好的纳米晶,通过对CdTe量子点合成反应条件的摸索,掌握了其合成的反应规律.同时用紫外分光光度计、荧光分光光度计和透射电子显微镜对其进行了表征.结果表明,回流时间、n(Cd2+):n(HTe-)、反应物浓度、TGA用量、反应体系pH值,对纳米晶的光学性质具有显著影响.回流2 h制得的CdTe纳米粒子直径约为5 nm,其发射峰窄且对称,表现出良好稳定的光学性质.     

纸浆纤维的表面电荷分布及测定

分析了漂白马尾松化学浆、漂白芦苇化学浆、马尾松热磨机械浆和废纸浆的长、中、短纤维含量以及它们的总电荷量和表面电荷量。结果表明浆种间纤维组分存在着较大的差别。纸浆纤维的总电荷量远大于表面电荷量,浆种间的电荷分布也大不相同,微细纤维的表面电荷量较高,木浆和废纸浆的表面电荷分布较均匀,芦苇浆的表面电荷量比木浆、机械浆和废纸浆的高,其长纤维组分与短纤维组分的表面电荷量相差较大。     

酸碱处理对SiC粉体表面性质的影响研究

本文建立了一种对SiC表面羟基浓度定量检测的方法,利用卡尔费休微量水分测定仪直接测量出SiC表面羟基浓度.经计算,本方法RSD为3.8％,对于SiC粉体表面羟基浓度测定能够得到满意的结果.通过X射线能谱仪(EDS)进行表面元素分析,表明酸碱处理使SiC粉体表面碳硅比趋向于符合化学式的1∶1.测量相同固相含量的SiC浆料粘度,数据表明经过酸碱处理过的SiC粉体使相同固相含量的浆料粘度降低.改变浆料的pH值可改变其粘度,找到了使SiC粉体流变性能最适宜的pH值.     

Surface modification of cellulose nanocrystals by grafting with poly(lactic acid)

The use of biopolymers obtained from renewable resources is currently growing and they have found unique applications as matrices and/or nanofillers in ‘green’ nanocomposites. Grafting of polymer chains to the surface of cellulose nanofillers was also studied to promote the dispersion of cellulose nanocrystals in hydrophobic polymer matrices. The aim of this study was to modify the surface of cellulose nanocrystals by grafting from L‐lactide by ring‐opening polymerization in order to improve the compatibility of nanocrystals and hydrophobic polymer matrices. The effectiveness of the grafting was evidenced by the long‐term stability of a suspension of poly(lactic acid)‐grafted cellulose nanocrystals in chloroform, by the presence of the carbonyl peak in modified samples determined by Fourier transform infrared spectroscopy and by the modification in C1s contributions observed by X‐ray photoelectron spectroscopy. No modification in nanocrystal shape was observed in birefringence studies and transmission electron microscopy. © 2013 Society of Chemical Industry     

Chemical vapor deposition derived ultralong SiC nanofibers: structural characterization and growth mechanism

In this study, the ultralong SiC nanofibers (SiC NFs) were synthesized through the sol–gel method assisted the chemical vapor deposition technique. The scanning electron microscope, transmission electron microscopy, X-ray diffraction, Raman, Fourier transform infrared, and X-ray photoelectron spectroscopy techniques were systematically employed to investigate the microstructure, morphology, and phase composition of the as-prepared products. The results demonstrated that the as-obtained products were β-SiC nanofibers with face-centered cubic crystal structure. Meanwhile, the ultralong SiC NFs present an average diameter of about 18 nm and a length up to several hundreds of micrometers and grew along the [1 1 1] direction with a planar stacking faults. In addition, we also investigated the formation mechanism and growth process of the ultralong SiC NFs. The successful preparation of such ultralong SiC NFs provides new idea for fabricating of other silicon-based ultralong nanofibers.     

Photoelectrochemical properties of hybrid junctions based on zinc phthalocyanine and semiconducting colloidal nanocrystals

In this paper, a photoelectrochemical study of hetero-junctions formed by zinc phthalocyanine (ZnPc) and semiconductor oxide nanocrystals (NCs), is reported. To this purpose, thin films composed of either size- and shape-controlled ZnO or TiO₂ NCs, synthesized by both hydrolytic and non-hydrolytic colloidal methods, were investigated as photo-anodes with ZnPc as the sensitizer. The effects of the oxide nature, of the nanocrystal shape and surface chemistry, and of the modality of photo-anode preparation on the resulting photoelectrochemical response were evaluated. In general, the photoactivity was found to be significantly enhanced when ZnO NCs were used as compared to TiO₂ NCs. In the latter case, the hetero-junctions based on non-hydrolytically prepared TiO₂ provided remarkably lower photocurrents with respect to those formed by its hydrolytically synthesized analogous. Moreover, a slight improvement of photoactivity was observed if spherical TiO₂ NCs were replaced by rod-like particles. Finally, as opposed to expectations, photo-anodes deposited from NC-ZnPc blended solutions exhibited a photoelectrochemical response comparable to that of sensitized films prepared by layer-by-layer procedure.     

基于核应用下碳化硅陶瓷及其复合材料的连接研究进展

SiC陶瓷及其复合材料凭借其自身固有的核辐射下的稳定性而有望成为新一代核裂变以及未来核聚变反应堆中重要的结构材料.能否满足核应用环境下各种苛刻条件而实现完美连接是其能够得到最终应用的关键.本文综述了目前国际上基于核应用上SiC陶瓷及其复合材料的几种连接工艺的发展情况.     

碳化硅量子点表面物化特性调控及其光学特性

采用化学偶联法,通过调整腐蚀剂组分及其相对含量,一步法实现了碳化硅量子点(SiC-QDs)表面物化特性的有效调控。研究表明:经硝酸(HNO_3)和氢氟酸(HF)混合腐蚀剂腐蚀纳米β-SiC粉末,通过超声空化破碎分散及高速离心处理,可获得SiC-QDs水相溶液,并一步法实现了表面修饰,在其表面形成了—COO、—OH等亲有机物功能基团。采用浓硫酸(H_2SO_4)为偶联剂,制备出表面具有巯基(—SH)的SiC-QDs水相溶液。腐蚀剂组分的相对含量对于SiC-QDs的光致发光强度与表面巯基的形成影响较大。在波长为340 nm的激发光激发下,SiC-QDs具有最大的发光强度,随着腐蚀剂中H_2SO_4含量的增加,其光致发光强度呈现降低趋势。当腐蚀剂的体积比为V(HF):V(HNO_3):V(H_2SO_4)=6:1:1时,制备的水相SiC-QDs表面既能稳定耦合—SH,又可以获得较高的光致发光强度。另外,对表面物化特性调控及其形成机制进行了分析研究。     

表面处理对碳化硅浆料流变性的影响

本文通过对SiC粉体洗涤、表面氧化和聚乙二醇(PEG)包覆等处理后制得的SiC浆料的zeta电位和粘度的测试,研究了表面处理对SiC粉体流变性能的影响.研究表明:通过用酸碱洗涤过后再经过在780℃氧化处理或经PEG包覆所得的SiC粉体,都可以使其浆料的zeta电位的等电点向酸性方向偏移,从而使在pH值为11.8时的电位差大幅度增加,改善了浆料的流变性能.而且用PEG包覆过的SiC粉体浆料的电位差增幅达20左右,使其流变性改善的效果更佳.     

非晶碳化硅量子点的制备及其光学性质研究

采用脉冲激光烧蚀法,以多晶3C-SiC陶瓷片为靶材,制备了悬浮于去离子水中的非晶SiC纳米颗粒.利用透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、傅里叶变换红外吸收光谱(FTIR)、紫外可见吸收光谱(UV-Vis)和光致发光谱(PL)等测试手段对其形貌、结构和光学性质进行了分析.结果表明:这些纳米颗粒由大量的非晶SiC构成,粒径在8～9 nm,光学带隙为3.28 eV;样品表现出较强的光致发光,发光峰位于415 nm处,这主要是由于量子限制效应造成的.