LaMer mechanism

Although the LaMer mechanism describes the different stages of nanocrystal nucleation and growth, it does not account for the kinetics of these processes. The kinetics of nanocrystal nucleation can be easily derived on the assumption that nuclei are spherical and grow isotropically. Then, the magnitude of surface free energy required to create a nanoparticle of radius r is ... 

Arrested precipitation can be performed in many different ways most simply, two solutions containing ions of a poorly soluble salt are mixed within a template. Alternatively, ions (or reactants) can be released slowly as described in stage 1 of the LaMer mechanism. Subsequently, nucleation and growth take place within the template. Furthermore, arrested precipitation can be combined with other methods of synthesis such as the sol-gel method. In that case, a gel is precipitated within the template and condensed in a second step. AU of these variations have been used to synthesise upconverting nanoparticles. 

Under certain conditions both the diffusional growth and the aggregative growth pathways may lead to monodispersed" systems. As mentioned earlier, the mechanism by which the former process could yield uniform particles was proposed by Victor K. LaMer (6), whose original scheme, reproduced numerous times, is shown in Figure 1.1.4. This kind of process is most likely operational in the formation of nanosized particles or larger amorphous spheres. 

Tamura, S., Brown, T. A., Whipple, J. H., Fujita-Yamaguchi, Y., Dubler, R. E., Cheng, K., and Lamer, J. (1984). A novel mechanism for the insulin-like effect of vanadate on glycogen synthase in rat adipocytes. J. Biol. Chem. 259, 6650-6658. 

LaMer, V. K., Dinegar, R. H. J. (1950). Theory, production and mechanism of formation of monodispersed hydrosols. Journal the American Chemical Society, 72, 4847—4854. 

Both LaMer s and the falling film aerosol generators yield only small quantities of products. Much larger amounts of aerosols can be produced by dispersing liquids with the help of various mechanical devices, e.g. rotating disks or ultrasonic nozzles [6]. These techniques, however, usually yield aerosols with broad distribution of droplet sizes and thus lead to polydisperse systems. The dispersion aerosol generators can, consequently, be used... 

As one would expect, the understanding of the mechanism of the formation of monodispersed colloids by precipitation has been of major concern to workers in the field. For a long time the concept developed by LaMer was generally accepted that is, such dispersions should be generated, if a short lived burst of nuclei in a supersaturated solution is followed by controlled diffusion of constiment solutes onto these nuclei, resulting in the final uniform particles. This mechanism is indeed operational in some, albeit limited, cases, and more often only at the initial stage of the precipitation process. 

Figure 3.6 Growth mechanism of nanocrystals (LaMer plot) showing different stages of growth.

Lamer VK, Dinegar RH (1950) Theory production and mechanism of formation of monodis-persed hydrosols. J Am Chem Soc 72 4847... 

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