As far as I know, surfactant molecules / ligand shell are usually "attached" to the nanoparticle surfaces in order to avoid direct contact of the magnetic "core" material of different particles. This need not prevent the formation of aggregates through dipolar interactions between particles. These are particularly strong if the particles are single domain and when the particle moment is locked to the atomic structure (is blocked, magnetic fluctuations being hindered by anisotropy barriers). So if you can choose, having superparamagnetic particles in solution will reduce their agglomeration by magnetic interactions.
As for size uniformity, it can be a formidable challenge and it also depends on what you call uniform. A variation in diameter of 5% is considered pretty good by many. But translate this to three dimensions and you get a volume variation (many a times the more important scale in magnetism) of 15% which sounds much less favorable.
There are many recipes but mainly two considerations (correct me if I'm wrong!):
You may be looking for a uniform size as resulting from equilibrium, then your chemistry is likely to be slow (on purpose) in order to provide and maintain near equilibrium conditions. For some examples, watch out for papers involving C. Amiens and/or B. Chaudret (LCC Toulouse, France).
And the 'opposite' is possible as well: control size uniformity by controlling and interrupting/quenching rapid kinetics. I have seen examples of such routes from the group of H. Weller (Hamburg, Germany).
Size control alone may not be sufficient though, in order to reach uniform ensemble properties. This is one of the lessons I've learned over the past years. More often than not, ensemble properties such as the distribtion of anisotropy barriers prove significantly broader than we would have guessed from the particle size alone. If uniformity at this level is what you're after, then after controlling size some further tuning of your chemistry might prove important to improve on the homogeneity of the magnetic characteristics.
That would depend on the material you want to synthesize nanoparticles of !
We do chemical reduction in order to get uniform stable particle using capping agent.
By chemical reduction of metal precursor (eg; Silver nitrate, Silver acetate etc for Silver nanoparticle preparation) using proper capping/ stabilizing agents. Other wise you can go for electrochemical preparation of nano particle, which can also give good results. But one should noted that the ratio of precursor and reducing agent in the reaction as well as amount of capping/ stabilizing agent plays a vital role on average size of nanoparticle, stability and homogeneity. So, I don't think anybody can propose a common method or procedure applicable for all nanoparticle preparation.
It depends on which particles you want to synthesize. I have previously made some gold nanoparticles (I think they were 8nm diameter) using the Frens method using HAuCl4 and sodium citrate under reflux (method and particle analysis can be found in Tetrahedron vol 64 pages 8476-8483 (2008))
It really depends on which metal you use. Do you want magnetic cobalt NPs? or Fe3O4 (which are super easy btw) Do you want to dope a semiconductor with magnetic ions? What are you trying to do with them?
hello! you can use the co-precipitation technique http://pubs.acs.org/doi/abs/10.1021/jp106811w, I use a combination of synthetic routes (micro-emulsion, reflux, hydrolisis) to obtain spinel metal oxides about 3-4nm in situ, but you look at nanoparticles of 25nm
I can't guarantee the size - but we do obtain very fine particles with nice magnetic properties by using relatively simple method called MGNP (Modified Glycine Nitrate Procedure)
Thermal decomposition of metal precursors in organic solvents.
Article Effect of Nanoparticle and Aggregate Size on the Relaxometri...
As far as I know, surfactant molecules / ligand shell are usually "attached" to the nanoparticle surfaces in order to avoid direct contact of the magnetic "core" material of different particles. This need not prevent the formation of aggregates through dipolar interactions between particles. These are particularly strong if the particles are single domain and when the particle moment is locked to the atomic structure (is blocked, magnetic fluctuations being hindered by anisotropy barriers). So if you can choose, having superparamagnetic particles in solution will reduce their agglomeration by magnetic interactions.
As for size uniformity, it can be a formidable challenge and it also depends on what you call uniform. A variation in diameter of 5% is considered pretty good by many. But translate this to three dimensions and you get a volume variation (many a times the more important scale in magnetism) of 15% which sounds much less favorable.
There are many recipes but mainly two considerations (correct me if I'm wrong!):
You may be looking for a uniform size as resulting from equilibrium, then your chemistry is likely to be slow (on purpose) in order to provide and maintain near equilibrium conditions. For some examples, watch out for papers involving C. Amiens and/or B. Chaudret (LCC Toulouse, France).
And the 'opposite' is possible as well: control size uniformity by controlling and interrupting/quenching rapid kinetics. I have seen examples of such routes from the group of H. Weller (Hamburg, Germany).
Size control alone may not be sufficient though, in order to reach uniform ensemble properties. This is one of the lessons I've learned over the past years. More often than not, ensemble properties such as the distribtion of anisotropy barriers prove significantly broader than we would have guessed from the particle size alone. If uniformity at this level is what you're after, then after controlling size some further tuning of your chemistry might prove important to improve on the homogeneity of the magnetic characteristics.
There is not a method which produces nanoparticles without agglomerates. The aglomerates can decrease with method of sample preparation. There is no technique for evaluating online agglomerates.
I was sythesizing metal nanoparticles on Al2O3 support once by reduction of appropriate salts in ethylene glycol in solvothermal conditions with microwave heating. Nanoparticles have diameter below 10 nm with low dispersion.
We have adopted sol gel method to synthesize titanium nano particles, agglomeration is controlled by the addition of acid, and particle size was dependent of gelatation time, the longer the gelation time produces smaller particles
Hope this ll give some idea
Muhammad Khan, I am also dealing with the sol-gel method , but to produce thin film , we obtained that the annealing temperature leads to agglomerate the particles. So, in this case the agglomeration is difficult to control.
Henceforth, the research community will be turned toward the strong electrostatic adsorption (SEA) developed by John R. Regalbuto. It effectively results in tightly distributed nanoparticles with no agglomeration or clusters. It is fast, effective, and reliably scalable.
Good luck in your work
As mentioned by Basurto above, whatever the method may be when used without surfactants produces some agglomeration. Methods like sonochemical, modified polyol etc. minimize agglomeration but their particle sizes are relatively larger. Thermal decomposition requires deoxygenated conditions, coprecipitation requires calcination; again the final crystallined products of both these methods contain certain agglomeration ald larger particle sizes. We can try sol-gel autocombustion in the presence of PEG, which does not require further heat treatments and the PEG may effectively contain both the particle growth and agglomeration.
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