Growing Uniform Colloidal Particles

Recently, a model has been developed that explains the size selection mechanism, which is based on experimentally accessible parameters, yet shows that particle uniformity can be achieved by aggregation (8). This mechanism assumes that the nuclei formed in a supersaturated solution rapidly grow to primary nanoparticles (singlets), which then aggregate into larger colloidal particles. Certain conditions must be met for the final products to be uniform in size. Thus, electrostatic repulsion of nanosize precursors must be mitigated or eliminated in the course of the process,... 

The major distinction between the model of La Mer and that developed for uniform latex particles lies in the incorporation of colloidal stability of small particles. The La Mer model assumes that each nucleus is colloidally stable and survives at the end of the reaction at the center of a particle. The aggregation models argue that stabilizing primary small particles is difficult, but aggregation does not necessarily result in a broad particle-size distribution. When schemes for control of particle-size distribution are developed, the result of accepting the notion that colloidal stability can play an important role is that attention is focused away from the length of the nucleation period and towards the colloidal properties of the growing particles. 

The use of colloidal metallic nanoclusters deposited onto solid substrates can provide a higher degree of control over the SPs spectral properties state-of-the-art results in the chemical synthesis showed, in fact, the possibility to grow nano-objects with high uniformity and low size dispersion [36-38], This can allow to fabricate extended substrates, in which the local morphology, and thus the resulting MEF effect, can be controlled with good precision [19, 39], As a counterpart, still some randomness is unavoidable in this approach, since it is not simple to define the position of the nanoclusters on the substrate with micrometer precision to realize, for instance, ordered arrays of metallic particles. 

The uniformity of size in the final colloidal system is all the greater as the nucleation stage (zone II) is short compared to the growth stage (zone III). Moreover, a diffusion growth mechanism for the particles explains why the diameters of small particles grow more quickly than those of larger ones. 

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