The Evolution of Branching during Flame Growth of Silica Aggregates
Amit S. Kulkarni1, Gregory Beaucage1, Hendrik K. Kammler2, and Sotiris E. Pratsinis2. (1) Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, (2) ETH Zurich, Sonneggstrasse 3, ML F25, Zurich, CH-8092, Switzerland
Nano-structures are formed under conditions far from equilibrium such as under deep quenches or at high temperatures as predicted by Gibbs-Thompson theory. Rapid, kinetically limited growth conditions are ideal to "lock-in" early stages of nano-structural formation. Pyrolytic synthesis offers an ideal mix of conditions for such nanostructural growth. Nano-particles formed under these conditions are prone to agglomeration and clustering into dense large particles making their potential size-related properties unavailable. Formation of rigid ramified aggregates is a serendipitous route to retention of nano-properties since these more open structures prevent collapse to dense agglomerates. Nano-aggregates are also common to nano-particles found in the environment such as soot and dust particles. Few advancements have been made towards understanding the kinetics of formation or even static descriptions of branching in aggregate structures despite the importance of aggregation to the end use of many nano-particles.
In this presentation, recent results will be discussed concerning the rate of aggregation and development of branching in aggregated nano-silica from USAXS measurements made during growth in premixed flames.