Experimental results of nanoparticle and crystal evolution during room temperature aging of aqueous suspensions that suggest growth by aggregation of nanoparticles, are presented. A kinetic mechanism suggest that the precursor nanoparticle population is distributed, and that 5-nm building units contributing most to aggregation only exist as and intermediate small fraction. The structure and role of these nanoparticles are of practical significance for the fabrication of hierarchically ordered porous materials and molecular sieve films. The proposed aggregation mechanism could lead to strategies for isolating or enhancing the concentration of crystal-like nanoparticles.
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Financial support for this work was provided by NSF (NIRT CTS-0103010 and CTS-05 22518). The HRTEM work was supported in part by NSF-MRI EAR-0320641 and the MRSEC Program of NSF under Award Number DMR-0212302. M.K. acknowledges support from NSF (DMS-041386). Characterization was carried out at the Minnesota Characterization Facility, which receives support from NSF through the National Nanotechnology Infrastructure Network. Numerical simulations were carried out using the facilities of the Supercomputing Institute for Digital Simulation and Advanced Computation at the University of Minnesota. We thank A. Parr for lending us the SAXSess instrument; F. S. Bates for providing access to SANS analysis at NIST and for helpful discussions; and R. Bedard, D. G. Vlachos, V. Nikolakis, R. F. Lobo and V. Hatzimanikatis for input at various stages of this work. Correspondence and requests for materials should be addressed to M.T. Supplementary Information accompanies this paper on www.nature.com/naturematerials.