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CAMP June Newsletter: Page 6

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Mechanisms for Shape Selection of Colloids and Nanoparticles Grown by Solution Synthesis


CAMP Professor Vladimir Privman has been conducting a joint research project with colleagues in the Ukraine. They are developing a three-dimensional model for diffusive growth of fine particles, the internal structure of which corresponds to different crystal lattices. A growing cluster is immersed in, and exchanges monomer building blocks with a surrounding medium of diffusing off-lattice monomers. Surface restructuring is accounted for by allowing (in addition to detachment) for monomer motion to the neighboring vacant crystal sites, according to rules mimicking local thermalization. This model has a key, new feature. It focuses on the growth of a single cluster, emerging as a crystalline core, without development of defects that can control large-scale growth modes of its faces. This single, defect-free core growth is imposed by the dynamical rules. The research results offer a possible explanation of the experimentally observed shape uniformity (i.e., fixed, approximately even-sized proportions) in the synthesis of uniform colloids and nanoparticles. The growth of particles in this work has demonstrated the basic principles of well-defined particle shape emergence. Specifically, several shapes are possible for a given crystal structure. Formation of shapes that follow the crystal symmetry and that are uniform, can be a result of the non-equilibrium nature of the growth process. See Figure 4. The shape of a growing particle can be controlled by varying the relative rates of the kinetic processes and by adjusting the concentration of the surrounding monomers.


Reference: Shape Selection in Diffusive Growth of Colloids and Nanoparticles, V. Gorshkov, A. Zavalov, and V. Privman, Langmuir (in print, 2009): http://dx.doi.org/10.1021/la900613p


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