Ostwald ripening is a "big fish-eats-small fish" phenomenon. The driving force is the minimization of the surface energy. In simple systems, the surface energy density gamma can be assumed independent of the shape, thus surface energy is directly proportional to surface. Ostwald ripening allows to minimize the exposed surface for a given amount of matter. Consider as a simple example, N atoms forming either a big spere of radius R or two smaller, identical spheres, each half the volume of the big sphere. The total volume will always be density*N.
In the former case the surface energy is sigma=4pi*gamma*R^2 which is lower than 2^(1/3)*sigma in the latter case (you just have to find the ratio between the radi).
If you have ever broken a mercury thermometer and you have tried to clean up you have seen a nice example of ostwald ripening....
Hi! The Ostwald ripening is the growth of the large particles on behalf of the small ones, that often occurs during the hydrothermal synthesis of the powder materials. Small-sized unstable particles are being dissolved and re-attached on the surface of the big particles, reaching more stable thermodynamic state. This effect decreases the surface area of the resulting powder.
According to the IUPAC, this process refers to ‘‘the growth of
larger crystals from those of smaller size which have a higher
solubility than the larger ones’’. H. C. Zeng,Curr. Nanosci., 2007, 3, 177–181
Ostwald ripening is a "big fish-eats-small fish" phenomenon. The driving force is the minimization of the surface energy. In simple systems, the surface energy density gamma can be assumed independent of the shape, thus surface energy is directly proportional to surface. Ostwald ripening allows to minimize the exposed surface for a given amount of matter. Consider as a simple example, N atoms forming either a big spere of radius R or two smaller, identical spheres, each half the volume of the big sphere. The total volume will always be density*N.
In the former case the surface energy is sigma=4pi*gamma*R^2 which is lower than 2^(1/3)*sigma in the latter case (you just have to find the ratio between the radi).
If you have ever broken a mercury thermometer and you have tried to clean up you have seen a nice example of ostwald ripening....
Following Giovanni in other words.The surface of a particle is made out of atoms/molecules that are less bound to the particles than the ones in the bulk. The smaller the particle the larger the weakening of the bond. The weakening of the binding is distributed along a diameter of the particle on a finite number of layers, this number is depending on the material. Therefore atoms/molecules from small particles dissolve more easily than the ones from large particles, while the atoms/molecules are more strongly bound to large particles. There is therefore a matter exchange that goes from the small particles to the larger ones.
What do you mean by "can ripening be controlled". What do you want to control?
@ Dr.Charles Hirlimann, As i understood ripening is a process of growing large particles from small ones or in other words exchange of matter from small particle to large particle, so it leads to reduction in surface area, my question is whether the aggregation of small particles can be controlled during the synthesis.
By using judicious and optimal quantity of capping agents or stabilizers, we can minimize Ostwald ripening.. but there's no universal stabilizer or capping agent.. its choice depends on your NP & solvents.
The risk of Ostwald ripening increase if your nanoparticles have relatively high aqueous solubility. An Ostwald inhibitor - a substance that is less soluble in water than your particle might be added and thereby increase the physical stabiltiy of the nanosystem.
Ostwald ripening is like real life: Siemens becomes bigger and bigger and a lot of small companies disappear. Area: The area of the lung is high, because there are a lot of small compartments. So when the number of particles or droplets decreases the surface area decrease as well. Influence: You can influence the surface properties of the particles or droplets. If there are ionic groups at the interface you can play around with concentration or the kind of counter ions. If the droplets are hydrophobic you can adsorb ionic surfactants to create a proper electrostatic repulsion, or you can use nonionics to influence the hydration forces. Another possibility is to create a surface mechanical barrier by adsorption of polymers.
Yes, you can do that, try to charge the surface so that you get a high Z-potential, that favour electrostatic repulsion, but it does not always help hindering Ostwald ripening.
Ostwald ripening is like real life. Siemens becomes bigger and bigger, and small companies disappear. Area: The area of the lung is high because there are a lot of small departments. So when the number of particles or droplet decrease the surface area of the main surface area decrease as well. Influence: You may change the surface properties of the particles or droplets. If there are ionic groups at the interface you may play around with concentration and kind of counteractions. You can increase the surface charge to create a proper electro-statical repulsion by adsorption of ionic surfactants. If the interface is hydrophobic you may influence the hydration forces by adsorption of nonionic surfactants. You can adsorb polymers to create a surface mechanical barrier..
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