Our recent work has demonstrated that an aerogelation process occurs in
acetylene diffusion flames and is responsible for the formation of millimeter
sized soot [1]. This work is the first demonstration of gelation in the aerosol
phase. Furthermore, our measurements indicate that the aggregates grow too
quickly (by a factor of 400) to be described by the Smoluchowski Equation (SE). Based on our previous measurements of the rate constant in
dilute aerosol
systems which were in agreement with kinetic theory [2), we concluded that this
too fast kinetics was a result of a breakdown of the SE as the system became
concentrated, i.e., as the gel point was approached.
The goal of our present work is to understand aggregation kinetics when a
particulate system becomes concentrated. Aerosols are the idea system for such a
study because, unlike colloids, there are no solvent mediate effects influencing
the particles. Moreover, this allows us to make direct comparison between
experiment and simulation. We are currently advancing our work on three fronts:
1) further studies of acetylene soot formation, 2) aggregation in dense TiO2
aerosols and 3) large-scale simulation of diffusion-limited cluster aggregation
in both two and three dimensional systems. Our preliminary simulations suggest
that a fast aggregation kinetics takes place for concentrated systems, while for
dilute system the aggregation kinetics is consistent with a mean-field kinetic
theory. Understanding . this fast kinetics in dense systems and the corresponding breakdown of the mean-field theory is the main motivation for the
theoretical research.
Sorensen, C., Chakrabarti, A., Hagemann, W., Fischbach, D., Shi, D., Fry, D., Gelation Kinetics in Aerosols, Fifth Microgravity Fluids Physics and Transport Phenomena Conference, NASA Glenn Research Center, Cleveland, OH, CP-2000-210470, pp. 1146-1147, August 9, 2000.