My previous graduate research at the University of Minnesota focused on the anisotropic growth of iron oxide nanoparticles via a nonclassical mechanism called oriented aggregation. Oriented aggregation is a special case of aggregation where the aggregating primary nanoparticles crystallographically align prior to fusing together to form new secondary single crystals.  Crystals formed by oriented aggregation often have a unique and symmetry-defying morphologies, can be twinned, and can contain stacking faults and other significant defects, all of which influence the physical and optoelectronic properties of the material. Through the semi-automated analysis of time-resolved transmission electron micrographs combined with statistical methods, we showed that increasing sodium nitrate concentration results in an increase of the second-order rate constant as does increasing the pH of the nanoparticle suspension towards the pH of zero net charge. However, the magnitude of the rate constant and the dependency of the influence of pH and ionic strength on the size of the primary particles do not follow expectations based on attractive Van der Waals & repulsive electrostatic interactions (DLVO theory). Through the use of cryogenic transmission electron microscopy (cryo-TEM), we demonstrated that oriented aggregation proceeds through three stages of aggregation, alignment, and fusion; and that the coordinative character of the suspending solvent appears to have the most substantial effect on the aggregation of the primary particles.My current postdoctoral research of the University of Illinois is focused on the seed-mediated anisotropic growth of gold nanorods. We are applying statistical methods (e.g. multivariate fractional factorial analysis), cryo-TEM, and additional methods to further understand the detailed mechanism of seed-mediated growth to improve the yield, reproducibility, monodispersity, and morphological purity of the product nanorods.My proposed primary investigator research builds on my expertise with cryo-TEM and related techniques to investigate mechanisms of nanoparticle aggregation to gain fine control over anisotropic nanoparticle formation through careful experimental design and statistical analysis.

Understanding and controlling nonclassical methods of anisotropic nanoparticle growth in liquid suspensions

248th National Meeting (2014)

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