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991.
Crystal growth and morphology of colloidal crystals of silica spheres (81.2 nm in diameter) are observed directly on a video-tape camera. Crystal growth from the round-shaped, small single crystals to the angular-shaped ones is clear. It is observable that the single crystals are packed densely and separated from each other with the grain boundaries. The morphology of colloidal crystals is quite similar to that of typical crystals such as metals, proteins, and ice. 相似文献
992.
Surface Modification of Nanometer Silica by N, N''''-dicyclohexyl- carbodiimide Mediated Amidation 总被引:1,自引:0,他引:1
Zhao Xia GUO Jie YU Jian YU* Institute of Polymer Science Engineering Department of Chemical Engineering Tsinghua University Beijing 《中国化学快报》2001,(10)
Nanometer silica has gained ever more attention for its superior properties over conventional micrometer particles and has been widely used as a filler in the manufacture of paints, rubber, plastics and so on1. However it is difficult to get silica mono- dispersed in the matrix due to heavy agglomeration. Surface modification through organic reactions is an efficient way to improve the dispersibility and compatibility with the matrix, thus improving the mechanical properties of the composite… 相似文献
993.
Rigidities of colloidal alloys of binary mixtures of colloidal silica spheres (CS82; 103 nm in diameter) with larger silica
spheres (CS91; 110 nm, CS121; 136 nm and CS161; 184 nm) have been measured by reflection spectroscopy in sedimentation equilibrium.
Substitutional-solid-solution-type alloy structures are formed for mixtures of CS82 and CS91 and for CS82 and CS121. A superlattice,
probably MgCu2 type, is formed for CS82 and CS161 mixtures. The rigidities of the colloidal crystals of the single component of the spheres
increase as the sphere size increases at the same number density of spheres. The rigidities of the colloidal alloys decrease
when a comparatively small number of the larger spheres are mixed with the small spheres at the same total sphere number density.
Received: 14 June 2000 Accepted: 3 November 2000 相似文献
994.
P. S. Thomas P. Šimon A. Smallwood A. S. Ray 《Journal of Thermal Analysis and Calorimetry》2007,88(1):231-235
The dehydration of an opal specimen was investigated
by thermogravimetric analysis (TG) in powder and bulk forms. The change in
geometry resulted in a significant difference in the temperature range in
which dehydration occurred with peak temperatures in the differential TG (DTG)
curve for the hand ground opal at 203°C and for the bulk opal at 340°C.
This difference was attributed to time taken for diffusion of free water in
the bulk opal to the specimen surface prior to evolution as a registered mass
loss. A model was proposed to account for the diffusion of water and was used
to estimate the diffusion coefficient. 相似文献
995.
Chenchen Zhou He Jia Shuaishuai Liang Yongjian Li Jiang Li Haosheng Chen 《Journal of polymer science. Part A, Polymer chemistry》2022,60(11):1750-1757
Polyhedral milliparticles (PMPs) have promising applications in self-assembly, tissue engineering, mechanical engineering, and photonics. The shapes and sizes of the PMPs have great impact on their functions. To date, the reported methods for adjusting the shapes and sizes of PMPs are still limited. Especially, it remains a challenge to fabricate the PMPs with high asymmetry. Here, we present a facile and efficient approach that focuses on the alteration of the relative positions between the microchannel and the UV light to tailor the shaping process of the PMPs. By tuning the rotation angle and translation displacement, a variety of monodisperse PMPs with both centrosymmetric and noncentrosymmetrical structures are synthesized, including tetrahedra, pentahedra, hexahedra, and so forth. Moreover, the polymeric PMPs are loaded with silica nanoparticles and further sintered into silica. The obtained silica PMPs hold great potential for the applications such as machining tools, abrasives, and electronics. 相似文献
996.
Satoshi Horino Tomoya Nishio Shinji Kawanishi Shinya Oki Koichi Nishihara Dr. Takashi Ikawa Dr. Kyohei Kanomata Karla Wagner Prof. Dr. Harald Gröger Prof. Dr. Shuji Akai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202202437
Natural lipases typically recognize enantiomers of alcohols based on the size differences of substituents near the carbinol moiety and selectively react with the R enantiomers of secondary alcohols. Therefore, lipase-catalyzed dynamic kinetic resolution (DKR) of racemic secondary alcohols produces only R enantiomers. We report herein a method for obtaining S enantiomers by DKR of secondary 3-(trialkylsilyl)propargyl alcohols by using a well-known R-selective Pseudomonas fluorescens lipase in combination with a racemization catalyst VMPS4, in which the silyl group reverses the size relationship of substituents near the carbinol moiety. We have already reported R-selective DKR of the corresponding propargyl alcohols without substituents on the ethynyl terminal carbon, and the presence of an easily removable silyl group has enabled us to produce both enantiomers of propargyl alcohols in high chemical yields and with high enantiomeric excess. In addition, immobilization of the lipase on Celite was found to be important for achieving a high efficiency of the DKR. 相似文献
997.
Martin Brodrecht Bharti Kumari Dr. A. S. Sofia Lilly Thankamony Dr. Hergen Breitzke Dr. Torsten Gutmann Prof. Dr. Gerd Buntkowsky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(20):5214-5221
The structure and surface functionalization of biologically relevant silica-based hybrid materials was investigated by 2D solid-state NMR techniques combined with dynamic nuclear polarization (DNP). This approach was applied to a model system of mesoporous silica, which was modified through in-pore grafting of small peptides by solid-phase peptide synthesis (SPPS). To prove the covalent binding of the peptides on the surface, DNP-enhanced solid-state NMR was used for the detection of 15N NMR signals in natural abundance. DNP-enhanced heterocorrelation experiments with frequency switched Lee–Goldburg homonuclear proton decoupling (1H–13C and 1H–15N CP MAS FSLG HETCOR) were performed to verify the primary structure and configuration of the synthesized peptides. 1H FSLG spectra and 1H-29Si FSLG HETCOR correlation spectra were recorded to investigate the orientation of the amino acid residues with respect to the silica surface. The combination of these NMR techniques provides detailed insights into the structure of amino acid functionalized hybrid compounds and allows for the understanding for each synthesis step during the in-pore SPPS. 相似文献
998.
Millimeter size γ‐Al2O3 beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al2O3 bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al2O3 beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al2O3 beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C16‐SO3H‐γ‐Al2O3–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H2O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr. 相似文献
999.
Chenchen Xing Dr. Jianlin Deng Wenlong Fu Dr. Jichao Li Lijie Xu Ruihao Sun Dan Wang Chengwen Li Prof. Kang Liang Meng Gao Prof. Biao Kong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(6):e202103642
Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu2+. DHBM-MSN exhibits an obvious quenching effect on Cu2+ in aqueous solutions, and the detection limit can be as low as 7.69×10−8 M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu2+ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications. 相似文献
1000.
Justin M. Gorham Tinh Nguyen Coralie Bernard Debbie Stanley R. David Holbrook 《Surface and interface analysis : SIA》2012,44(13):1572-1581
The photo‐induced, physicochemical surface transformations to silica nanoparticle (SiNP) ‐ epoxy composites have been investigated. The silica nanocomposites (SiNCs) were prepared using a two‐part epoxy system with a 10% mass fraction of SiNPs and exposed to varying doses of high intensity, ultraviolet (UV) radiation at wavelengths representative of the solar spectrum at sea level (290 nm to 400 nm) under constant temperature and humidity. Visibly apparent physical modifications to the SiNC surface were imaged with scanning electron microscopy. Surface pitting and cracking became more apparent with increased UV exposure. Elemental and surface chemical characterization of the SiNCs was accomplished through X‐ray energy dispersive spectroscopy and X‐ray photoelectron spectroscopy, while attenuated total reflectance Fourier transform infrared spectroscopy revealed changes to the epoxy's structure. During short UV exposures, there was an increase in the epoxy's overall oxidation, which was accompanied by a slight rise in the silicon and oxygen components and a decrease in overall carbon content. The initial carbon components (e.g. aliphatic, aromatic and alcohol/ether functionalities) decreased and more highly oxidized functional groups increased until sufficiently long exposures at which point the surface composition became nearly constant. At long exposure times, the SiNC's silicon concentration increased to form a surface layer composed of approximately 75% silica (by mass). Published 2012. This article is a U.S. Government work and is in the public domain in the USA. 相似文献