共查询到20条相似文献,搜索用时 15 毫秒
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Ceren Susut Thuy Dang Nguyen George B. Chapman YuYe Tong 《Journal of Cluster Science》2007,18(4):773-780
Based on a polyol process, one-step synthetic procedures were investigated for concomitant control of the shape and size of
platinum nanoparticles (Pt NPs). Cubic and octahedral/tetrahedral particles of different sizes (5–10 nm) were synthesized
using these procedures. Further attempts to control the shape of the NPs below 3–4 nm failed. It was found that 3–4 nm is
the particle size limit for Pt NPs above which the particle size and shape can be concomitantly controlled. 相似文献
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Knecht MR Sewell SL Wright DW 《Langmuir : the ACS journal of surfaces and colloids》2005,21(5):2058-2061
One of the most significant challenges facing the biomimetic synthesis of materials is achieving the requisite level of dimensional and spatial control. Typical reaction conditions for biomimetic silica synthesis allow for continued growth and ripening leading to the formation of larger nanospheres on the order of 200-600 nm in diameter. Herein, we have used polyamidoamine and polypropylenimine dendrimers as templates to expand the reaction conditions of biogenic silica production to produce a more robust synthesis leading to size-selective precipitation of silica nanospheres. Through the use of defined concentrations of phosphate buffer and main group metal chloride salts, we have shown that the biomimetic silica growth process is controlled by cationic neutralization of the anionic silica nanosphere surface. Neutralization minimizes electrostatic repulsions, allowing for agglomerization and continued growth of nanospheres. By controlling these concentrations, we can selectively produce silica nanospheres of desired dimensions between 30 and 300 nm without adversely affecting the template's activity. 相似文献
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V. A. Kuznetsov A. G. Lipson V. A. Klyuev D. M. Sakov Yu. P. Toporov Yu. S. Simakov 《Russian Chemical Bulletin》1989,38(7):1340-1343
1. | It has been determined experimentally that for a given level of power input, the limiting surface area Smax achieved in size-reduction increases, and the rate constant for the size-reduction of metal halide crystals decreases with increasing bond energy of the crystal lattice in the order KCl < nacl="">< naf="">< lif.=""> |
2. | A parameter is proposed for describing the size-reduction of metal halides both in the step in which destruction is overcome, and in the process in which dynamic equilibrium is established between the processes of particle dispersion and aggregation. |
3. | Relationships have been obtained that make it possible to calculate precisely Smax for any metal halide with the NaCl structure by using the Smax value of any other metal halide regardless of its defect structure. |
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GuoKangLI XiaoFangLI YongJIANG MeiZhenZENG EnYongDING 《中国化学快报》2003,14(9):977-978
Natural cellulose with the crystal form of cellulose I, when treated with condensed lye(e.g. 18% NaOH), can change into new crystal form of cellulose II. But the nano-crystaUinecellulose (NCC) can do it when only treated with dilute lye (e.e. 4%NaOH) at room temperature and even can dissolve into slightly concentrated lye (e.g.4%NaOH). 相似文献
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《液相色谱法及相关技术杂志》2012,35(16):3305-3319
Abstract We report here a new chromatographic method for characterization of polyamides and polyether-block-amide copolymers by Size Exclusion Chromatography. First, it concerns absolute characterization of polyamide probes by classical light scattering and Ubbelohde viscometry measurements and the choice of narrow distribution standards to calibrate the GPC system. The GPC analysis of polyamides 6, 11, 12 and copolymers is based upon the dual detection refractometer/on-line continuous viscometer at 130°C using columns packed with cross-linked polystyrene gels, benzyl alcohol as mobile phase and polytetrahydrofuran standards for calibration. The main results are absolute average molecular weights and distribution curve, intrinsic viscosity and viscosity law. In addition, viscometric data produced evidence of long-chain branching occuring beyond a limiting molecular weight in some polyamide 12 samples. 相似文献
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使用4种应用较为广泛的激光粒度仪(Mastersizer2000、Bettersize2000、Horiba LA950和LS13320)对粒度差异较小的下蜀土(土塘剖面)进行了测试,从而对比分析不同激光粒度仪对于下蜀土的粒度组成测试差异及其这种差异对研究结果可能产生的影响.结果表明:对粉砂颗粒组分的分析,4种激光粒度分析仪分析结果的差异最小,而对砂和粘土颗粒组分分析的差异最大.就粒度频数曲线、概率累积曲线、粒度组分、C-M图、粒度参数散点图及粒度参数剖面垂向变化等统计参数与统计方式而言,4种仪器的测试结果均有一定的差异,其中,概率累积曲线、粒度参数散点图差异较大.粒度参数的剖面变化差异也较大,影响了对剖面的阶段性划分,这在一定程度上影响了研究结果,造成使用不同仪器,可能会得出不同的结果. 相似文献
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Leonardo Soriano Petri P. Ahonen Esko I. Kauppinen Jorge Gómez-García Carmen Morant Francisco J. Palomares Marta Sánchez-Agudo Patrick R. Bressler José M. Sanz 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):849-857
Summary. A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present
the characterization of TiO2 nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed
by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles
crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase
and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM
images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles
formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data.
Received October 5, 2001. Accepted (revised) December 6, 2001 相似文献
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Molecular weight distributions of the cationic polyelectrolyte poly(2-trimethylammonium ethyl methacrylate chloride) were determined via size exclusion chromatography (SEC) for a very broad molecular weight range (). Non-size exclusion effects (ion inclusion, ion exclusion, adsorption) were controlled by special surface treatment of the stationary phase (DMAE-FractosilR, E. Merck) and by proper selection of the mobile phase. A non-linear effective molecular weight calibration procedure was applied to account for the high polydispersity of the polyelectrolyte standard polymers. data from SEC experiments agree with results from light scattering, and the molecular weight distributions obtained from SEC and sedimentation velocity analysis compare well. 相似文献
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K Kooser DT Ha E Itälä J Laksman S Urpelainen E Kukk 《The Journal of chemical physics》2012,137(4):044304
The electronic structure and photofragmentation in outer and inner valence regions of Se(n) (n ≤ 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectron-photoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se(n) microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se(n) clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies. 相似文献
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Isabelle Lisiecki 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):499-507
In this review, we show that the use of AOT reverse micelles favors the formation of spherical metallic nanomaterials, magnetic or not, such as cobalt and copper. The size is controlled by varying different parameters like the water content of the micelles, the intermicellar interactions, the capping with the AOT surfactant and the reducing agent concentration. As expected theoretically, the change in size of copper nanocrystals induces changes in their optical properties. By controlling both the size and the size distribution of cobalt nanocrystals, well-defined, two-dimensional superlattices can spontaneously form. 相似文献
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《Journal of Dispersion Science and Technology》2013,34(5):726-735
ABSTRACT The principles of aerodynamic time-of-flight particle size characterization are reviewed, and the associated mechanics are illustrated for a commercially available instrument system. Examples are illustrated for pharmaceutical and titania samples. Future applications for time-of-flight measurements in combination with other measurement techniques are discussed. 相似文献
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在制备高硬度、高热导、耐磨、耐腐蚀、耐高温的新兴陶瓷材料氧化硼、氮化硅的固相反应中,氮化镁是不可缺少的烧结助剂[‘,’j.同时,氮化镁还可用于制备发泡合金和回收核废料等领域.目前氮化镁的制备方法有:镁粉直接与氮气反应法[‘,‘1、镁在氮等离子流中与氮反应法*‘、在氮气气氛下镁线圈爆炸法‘’‘和低压化学气相沉积法[’j.在上述方法中,有些方法需要复杂和昂贵的设备.有些方法得到氮化镁的产率较低.镁粉直接与氮气反应是具有工业生产价值的方法一然而,这种方法需要SOO”C到gOO”C的高温.我们曾经报道过利用温和… 相似文献
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在前期工作的基础上, 利用导电原子力显微镜法测量单根聚苯胺纳米线的电导率, 探讨了聚苯胺纳米线(PANI nanowine)电导率的尺寸效应, 发现尺寸效应与纳米线的有序性有关. 相似文献
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There is considerable interest in using size exclusion chromatography (SEC) to analyze and purify specific plasmid isoforms, but there is currently no fundamental understanding of the effects of plasmid size and morphology on plasmid behavior in SEC. Experiments were performed for plasmids from 3.0 to 17.0 kbp in size. The linear and open-circular isoforms were generated from the supercoiled plasmid by appropriate enzymatic digestion. SEC retention data were obtained using a Sephacryl S-1000 SF resin packed column and an Agilent HPLC system over a range of flow rates using buffers of different ionic strength and composition. The plasmid partition coefficients, KP, were evaluated from the first statistical moment of the chromatographic peak. The partition coefficient decreased with increasing plasmid size as expected; KP varied from 0.299 to 0.045 for supercoiled plasmids of 3.0 to 17.0 kbp. The partition coefficient also increased with increasing ionic strength due to the compaction of the DNA associated with the shielding of the intramolecular electrostatic interactions. For any plasmid size, the supercoiled isoform had the highest KP followed by the open-circular and then the linear isoform, consistent with independent estimates of the plasmid radius of gyration as determined by static light scattering. The experimental data were analyzed using available theoretical models for the partitioning of linear and cyclic polymer chains in well-defined pore geometries. These results provide important insights into the behavior of different plasmid isoforms in size exclusion chromatography. 相似文献
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P. A. Chernavskii V. I. Zaikovskii G. V. Pankina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(8):1274-1280
The dynamics and kinetics of formation of iron carbides in Fe/SiO2 catalysts during the hydrogenation of CO and in a topochemical reaction between Fe and CO was studied. The effective activation energy of carbide formation was found to increase as the size of iron particles decreased. Alternative hypotheses explaining the observed size effect are suggested. 相似文献
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Kazuyoshi Nakamura Asako Uemoto Toyoko Imae Conxita Solans Hironobu Kunieda 《Journal of colloid and interface science》1995,170(2)
The stability and size control of reverse vesicles have been investigated for a sucrose monoalkanoate/hexaethylene glycol hexadecyl ether/decane/water system. The stability is highly dependent on the surfactant mixing ratio, amount of added water, and vesicle size. The size distribution of reverse vesicles produced by simple mixing is very large, but larger vesicles can be removed by means of the extrusion method and reasonably homogeneously size-distributed reverse vesicles can be obtained. If a probe-type ultrasonicator is used, the reverse vesicles obtained are homogeneous and of very small size (50-70 nm in diameter) and they are considered to be of the unilamellar type. 相似文献