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nanoquebec 2006-11-22 09:10

纳米粒子的团聚及其机理和对策

[size=4][b][背景][/b][color=Green]纳米粒子的团聚是纳米粒子材料加工和应用中普遍存在的一个重要问题,目前对其团聚的机理虽然有比较好的了解,但很不完善,而且有一些相互矛盾的看法.虽然团聚在很多情况下是要防范的和不希望的,但在有些情况下则需要利用团聚现象. 本主题想收集这方面的研究信息和其进展[/color].[/size]WP6\'N0S] p
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[size=4]本专题希望讨论一下问题:
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1.团聚现象及其形成机理
2.团聚的控制方法
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欢迎大家分享和讨论．　[size=5][b]最终我们可以写个总结（希望有人合作！）[/b]．[/size][/color]

nanoquebec 2006-11-22 09:28

先转载两个最近的关于研究纳米粒子团聚的研究项目
[quote]
[b]1. NIRT: Multi-Scale Simulation of Nanoparticle Aggregation for Scale-Up of High-Rate Synthesis Methods[/b]HA0pu[{$n\
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Fox, R. O. Gordon, M. S. Lamm, M. H. Narasimhan, B. Subramaniam, S. Vigil, D. R. 1JoyN:R5si
[i]National Science Foundation, 8/1/2004 to 7/31/2006[/i]
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Nanoparticles are the basic building blocks for many novel materials. In nearly all high-rate synthesis methods for nanoparticles, chemical precursors are brought together by turbulent mixing to form particle nuclei that grow rapidly due to surface addition and aggregation. Next-generation applications of nanoparticles will require precise control of product quality when synthesis methods are scaled up. Predicting nanoparticle aggregation starting with detailed knowledge of [b]particle surface chemistry and the time-dependent shear rate[/b] in a turbulent flow is the key step for scale-up of high-rate synthesis methods. In this project, an international, interdisciplinary team of scientists and engineers will develop and validate multi-scale computational tools based on fundamental chemical and physical models that can predict a priori the properties of nanoparticle clusters produced after scale-up of high-rate synthesis methods. The computational approaches range from quantum calculations of particle surface chemistry (atomic to molecular scale), to Brownian dynamic simulations of nanoparticle aggregation with and without shear (nano to micron scale), to direct-numerical and large-eddy simulations of the particle size distribution in turbulent flow (micron to macro scale). The experimental validation approaches range from direct measurements of the interparticle potentials using atomic force microscopy, to measurements of the cluster size distribution in quiescent systems using light scattering, to in situ measurements of cluster size and fractal dimension in Taylor-Couette flow. The model system to be investigated is monodisperse colloidal functionalized latex nanoparticles. The nanoparticles will be synthesized in our lab with a view to carefully modulate and understand aggregation mechanisms in this system. Three types of functionalized nanoparticles will be investigated: (1) unmodified latex, (2) sulfonated latex, and (3) carboxylated latex; and the extent of surface coverage will be varied to probe the effect of surface chemistry on nanoparticle aggregation mechanisms. The addition of these functionalities modifies the hydrophobic surface of the latex particles and enables interrogation of aggregation mechanisms in mixtures of unmodified and modified nanoparticles. The choice for the model system is also driven by our ability to perform detailed ab initio quantum calculations of surface-surface, surface-molecular, and molecular-molecular interactions between surface-modified latex nanoparticles. Using this detailed atomistic description of nanoparticle surface chemistry, we will develop coarse-grained interparticle potential models for use in Brownian dynamics simulations to predict cluster size distribution and cluster morphology in shear flow. From this information, aggregation kernels needed for the Smoluchowski equation will be extracted and implemented in the general dynamic equation for particle aggregation in turbulent flow. At each step of model development, appropriate experimental validation tests will be carried out to ensure that the multi-scale simulation tools agree with reality. The intellectual merit of the proposed activity is that the rational design and scale-up of nanoscale synthesis and processing methods is a crucial step toward the commercial viability of nanoparticles for widespread technological applications, and by developing and validating multi-scale, multi-phenomena simulation tools, this project will demonstrate for the first time the capability to predict the properties of nanoparticles produced by high-rate synthesis methods after scale-up starting from the fundamental chemical and physical theoretical models. The interdisciplinary team assembled to attack this problem is uniquely qualified to bridge the enormous range of length and time scales, and the corresponding numerical and experimental challenges, that are required to successfully accomplish this task. The broader impacts of the proposed activity are that this project will lead to the development of new courses in nanoscale science and technology at the participating universities. Undergraduate education will be enhanced through an REU program in computational chemistry, physics, and mathematics at Iowa State and outreach programs (CoS, APEXES, MCSRO) at the University of Minnesota. Graduate education will be enhanced by internship programs with industrial and international partners and the IGERT for nanoparticle science and engineering at Minnesota. K-12 outreach and recruitment of minorities and women will be actively pursued through participation in the LEAD, Science Bound, and PWSE programs at Iowa State and similar programs at Minnesota. Results from the project will be disseminated broadly through the industrial and international partnerships, dedicated sessions at professional meetings, annual nanoscale science and engineering workshops, and archival publications. Research and education themes addressed in this proposal (in order of significance) are: (1) manufacturing processes at the nanoscale, (2) multi-scale, multi-phenomena theory, modeling, and simulation at the nanoscale, and (3) nanoscale processes in the environment.,k\}NA2L^U
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[quote][b]2. Nanoparticle Aggregation: Development of an Integrated Model to Assess System Performance in Solid-Liquid Separation and Related Processes[/b]

[color=Blue]Overview[/color]

The project aims to study the roles of particle and fluid properties, as well as chemistry in the [color=Red]aggregation behaviou[/color]r of particulates, focusing on the nano-sized regime where fundamental knowledge is still required. The understanding will be used to develop an engineering model to correlate aggregate properties and process conditions for control and scale-up purposes. The outcomes will be relevant not only for solid-liquid separation, but also for the synthesis of nanomaterials and functionalisation of particles for specific applications, including bio-separation/transformation.
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Another goal is to develop a methodology to forecast overall solid-liquid separation system performance from their microscopic properties, such as quantifying filtration behaviour through pore analysis of a filter cake, and understanding the fluid transport phenomena during process. The use of 3D-imaging to visualise complex structures at small length scales and fine resolution will enable a more realistic modelling approach, through integration with a robust simulation tool like the Lattice-Boltzmann method.

[color=Navy]Major Achievements in 2004[/color]

Aggregation studies on nano- and micro-sized particles under a controlled shear environment showed the effects of restructuring in fractal aggregates behaviour and properties, even for systems previously regarded as too small to experience any modifications due to macroscopic shear. This knowledge will have significant implications for mechanical separation processes involving compressible biomaterials, such as proteins or cellular matters. A novel methodology to characterise relative aggregate strength has been proposed, and its application demonstrated for a range of particulate systems (latex, silica, and coal particles) (Selomulya et al., Hermawan et al.). Another study was conducted on the precipitation and aggregation mechanisms of iron hydroxide particles during neutralisation. Specific process conditions were identified to produce desirable solid properties to enable better solid-liquid separation (Selomulya et al.). The study has subsequently been accepted for publication (Gan et al.).

3D visualisations of microstructures with techniques such as optical confocal laser microscopy and high resolution X-ray microtomography enable direct computation of solids assembly properties and their permeability to fluids. A specific application involving aggregate formation and sediment networks was attempted, from which the behaviour of sediments containing these materials can be predicted on the basis of a bench-top test and the use of a Lattice Boltzmann simulation (Selomulya et al.). The ability to derive performance information, such as fluid permeability from laboratory based measurements of microstructure coupled with appropriate micro-scale physical simulations has considerable potentials. One example is to predict trends such as the filtration behaviour of porous structures under different states of compression. This offers a significant benefit in assisting the formulation design of flocculated materials pertinent to a number of industrial sectors wishing to design optimal filtration or relevant operations. The project is in collaboration with Prof. Richard Williams and Dr. Xiaodong Jia from the Institute of Particle Science and Engineering (IPSE), University of Leeds.!cPT%@"nU1\F

Future Plans and Directions
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* Aggregation and aggregate characterisation:Study into the mechanisms, hydrodynamic behaviour, aggregate characteristics, and implications to macro-properties such as sediment consolidation, centrifugation, and filtration. i F%S+RaY
* Simulation and modelling projects: Integration of imaging and modelling tools to predict system performance from micro-properties.
* Magnetic nanoparticles: Functionalisation of nano-sized magnetite for selective bioseparation and biotransformation.%`,R,T}2A\5J
* Treatment of acid mine drainage: Mechanisms of iron hydroxide precipitation, effects of the presence of other metal ions, optimum process parameters for sludge densification.[/quote]
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[[i] 本帖最后由 nanoquebec 于 2006-11-21 21:03 编辑 [/i]]

nanoquebec 2006-11-22 10:15

一篇介绍控制纳米粒子团聚的文章,GN V7d~"Gk
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[align=center][size=4][color=Green]Controlling nanoparticle aggregation[/color][/size]xmf)mhU8S
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Shell-crosslinked nanoparticles with a remarkable rosette shape have been formed using a simple and elegant technique.
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Karen Wooley from the University of Washington, US, used a radical polymerisation reaction between maleic anhydride and styrene to form block copolymers. The particles they made had an unexpected and unusual rosette structure. o L$M'P'k#m9JA:uM
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nanoparticles

Initially the reaction formed micellar structures; crosslinking followed to produce shell-crosslinked nanostructures. The synthesis is a simple one pot reaction, without any need for separate additions of the reagents. This labour saving technique is cheaper and more efficient than any method used for preparing similar structures to date.

The impetus of this work came from a need to simplify the production of these versatile and well studied crosslinked structures. The ordered rosette pattern was seen using tunnelling electron microscopy. Wooley thinks the pattern arises from the internal arrangement of the polystyrene core. This structural complexity could have huge potential for areas as diverse as nanoreactors and drug delivery. V2h"dZ3K0P2` X
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Wooley said these remarkable nanoparticles might ‘open the door to a greater degree of control over the way nanoparticles aggregate into larger assemblies than has hitherto been possible’.
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In future, Wooley hopes her group’s work will establish how the rosettes form. She also wants to investigate the effects that higher-order structure can have on the properties of the nanoparticles. Sophia Anderton ,l'h^+^-Sd
References
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S Harrisson and K L Wooley, [i]Chem. Commun[/i]., 2005 (DOI: 10.1039/b504313a)[/quote]

[[i] 本帖最后由 nanoquebec 于 2006-11-21 21:19 编辑 [/i]]

nanoquebec 2006-12-02 06:21

收集在这里vu6W-Dx*p-zT
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Reports"loCPY^MX
[b]General Strategies for Nanoparticle Dispersion[/b].}{d])C$cY
[i]Science [/i]24 March 2006:， Vol. 311. no. 5768, pp. 1740 - 1743
DOI: 10.1126/science.1122225
Michael E. Mackay,* Anish Tuteja, Phillip M. Duxbury, Craig J. Hawker, Brooke Van Horn, Zhibin Guan, Guanghui Chen, R. S. KrishnanSy}U3G]*w ?
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Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.m]S{+um8I1h

[url=http://www.box.net/public/ar8bhl5thf]:downloads:pdf:box[/url][/size]
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[[i] 本帖最后由 nanoquebec 于 2006-12-01 17:23 编辑 [/i]]

vic321try 2006-12-06 00:42

非常好得话题，值得去仔细学习:victory: :victory:

zhangdelin0000 2006-12-06 11:04

Org. Biomol. Chem., 2006, 4, 3435 - 3441, DOI: 10.1039/b605799c

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Design of asymmetric DNAzymes for dynamic control of nanoparticle aggregation states in response to chemical stimuli7COWI.l%A
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Juewen Liu and Yi Luyj Z+?/Bq5PA'|

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Dynamic control of nanomaterial assembly states in response to chemical stimuli is critical in making multi-component materials with interesting properties. Previous work has shown that a Pb2+-specific DNAzyme allowed dynamic control of gold nanoparticle aggregation states in response to Pb2+, and the resulting color change from blue aggregates to red dispersed particles can be used as a convenient way of sensing Pb2+. However, a small piece of DNA (called invasive DNA) and low ionic strength (30 mM) were required for the process, limiting the scope of application in assembly and sensing. To overcome this limitation, a series of asymmetric DNAzymes, in which one of the two substrate binding regions is longer than the other, has been developed. With such a system, we demonstrated Pb2+-induced disassembly of gold nanoparticle aggregates and corresponding color change at room temperature without the need for invasive DNA, while also making the system more tolerant to ionic strength (33–100 mM). The optimal lengths of the long and short arms were determined to be 14 and 5 base pairs, respectively. In nanoparticle aggregates, the activity of the DNAzyme increased with decreasing ionic strength of the reaction buffer. This simpler and more versatile system allows even better dynamic control of nanoparticle aggregation states in response to chemical stimuli such as Pb2+, and can be used in a wider range of applications for colorimetric sensing of metal ions.

zhangdelin0000 2006-12-06 11:05

图片怎么传不上去？

zhangdelin0000 2006-12-06 11:09

. Phys. Chem. B, 109 (31), 14755 -14758, 2005. 10.1021/jp051177o S1089-5647(05)01177-6
Web Release Date: July 15, 2005 K{A;z+[p5lWte

Copyright © 2005 American Chemical Society
Adsorbate-Induced Silver Nanoparticle Aggregation Kinetics N1I!@A[

Martin Moskovits*

Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 "B*j7PQ(r
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Blanka Vlková

Department of Physical and Macromolecular Chemistry, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic 4f ]L9J9~+K

Received: March 7, 2005

In Final Form: July 3, 2005pv9YQ,N,V0_

Abstract:

Metal sols are often stabilized in solution by the presence of a charged double layer surrounding each colloidal nanoparticle that produces a coulomb barrier to aggregation. The nanoparticles can be induced to aggregate by replacing the charged surface species by uncharged adsorbate. We present a simple analysis that produces an expression for the initial rate constant describing the aggregation process, which is shown to depend nontrivially on the adsorbate concentration. The expression is tested experimentally by following and analyzing the time rate of decrease of the surface plasmon resonance absorption of isolated Ag nanoparticles in aqueous solution. The experimental result accords well with theory, producing a rough estimate of the (adsorbate-concentration dependent) barrier to aggregation that in the absence of added adsorbate is approximately equal to 0.08 eV.

nano 2006-12-06 11:19

[quote]原帖由 [i]zhangdelin0000[/i] 于 2006-12-05 22:05 发表+bCKSOj}f&S
图片怎么传不上去？ [/quote]J:EN&O&v'p
看看这里，~h f*B d
[url=http://www.nanost.net/bbs/thread-371-1-1.html]http://www.nanost.net/bbs/thread-371-1-1.html[/url]A J f Pn,n
图片不用上传到这里，只要传到一个公用空间就可以了。

zyhn2002 2006-12-21 16:26

确实是个好的话题，我在实验中就遇到过，不过我还没有有用的体会啊

zyhn2002 2006-12-21 16:33

一篇这方面的文章

Preparation of hard agglomerates free and weakly agglomerated antimony by coprecipitation reaction~W6w W xd
Materials Chemistry and Physics 97 (2006) 452–457(M{C/[ |C+F*f1~oP
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[size=3][color=DarkGreen][b]Preparation of hard agglomerates free and weakly agglomerated antimony doped tin oxide (ATO) nanoparticles by coprecipitation reaction in methanol reaction medium[/b]

Dae-Wook Kima, Deok-Soo Kimb, Young-Gon Kima, Young-Chai Kima and Seong-Geun Oha, Corresponding Author Contact Information, E-mail The Corresponding Author
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aDepartment of Chemical Engineering, Hanyang University, Seoul 133 791, Republic of Korea%N`|yjvlF+B'^:O
bVoronoi Diagram Research Center, Department of Industrial Engineering, Hanyang University, Seoul 133-791, Korea
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[i] [/i][b][i]Materials Chemistry and Physics[/i][/b], Volume [b]97[/b], Issues 2-3 , 10 June 2006, Pages 452-457

Abstract&OKy6l%D;s[
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Antimony doped tin oxide (ATO) nanoparticles were prepared by coprecipitation reaction in methanol solution of tin(IV) chloride pentahydrate and antimony(III) chloride. The obtained ATO nanoparticles did not form any secondary particles and showed loosely agglomerated structure consisting of primary particles weakly attached with each other by van der Waals and capillary adhesive forces. In addition, ATO nanoparticles showed lower degree of agglomeration compared with those of commercial product. The reason for the formation of weakly agglomerated structure was discussed. 1q^9cZ Gr?\
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[color=Red]To prevent formation of hard agglomerates, the main reaction medium was changed from water to methanol and the obtained precursor precipitates were washed with methanol. Although changing the reaction medium from water to methanol could not prevent the precursor primary particles from agglomerating due to extremely small size, it can reduce the strength of the precursor agglomerates by preventing hydrogen bonding between particles. The removal of all nonbridging hydroxyl groups at the precursor particle surface results in the prevention of formation of hard agglomerates by means of inhibition of formation of solid bridges between the precursor primary particles during calcination.[/color]B*Z^"g?Sv
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As a result, densely packed and weakly agglomerated precursor precipitates were transformed into ATO nanoparticles that did not form any secondary particles and showed loosely agglomerated structure consisting of particles weakly attached with each other by van der Waals and capillary adhesive forces after calcination and light milling process. Furthermore, ATO nanoparticles showed lower degree of agglomeration compared to those of commercial product. xAr:|r}.fm
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[url=http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TX4-4J3WS20-4-F&_cdi=5580&_user=2101137&_orig=browse&_coverDate=06%2F10%2F2006&_sk=999029997&view=c&wchp=dGLzVzz-zSkzV&md5=2a4a199a145af27fbcdbde585ff8e039&ie=/sdarticle.pdf]:fulltext pdf[/url])r3kW!S!n8R A

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nano 2007-01-27 00:02

查看完整版本: 纳米粒子的团聚及其机理和对策

纳米粒子的团聚及其机理和对策

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