(339r) Analysis of the Surface Shielding of Fractal Like Particles

Surface characteristics of nanoparticles play a key role in their performance and can effectively influence their transport characteristics. Furthermore, selective deposition of desired materials can increase the functionality of tailor-made particles or prevent toxic implications retaining however their performance (e.g. opacity of TiO2 particles without undesirable photocatalytic activity by their coating with nanothin layers of SiO2 [1,2]). Furthermore, the superparamagnetic activity of Fe2O3 nanoparticles can be retained by similar coatings that allow their ready incorporation in polymer matrices for actuators or biomedical applications [3]. Also Heine and Pratsinis [4] simulated the growth of silica agglomerates with fractal dimension Df=1.8 and showed that even for low initial concentrations, agglomerates upon growth can effectively occupy far more volume than a mass equivalent sphere so their coagulation can lead to gelation within 3-4 seconds. This work investigates deposition on generated agglomerates in the free-molecular regime through analysis of the surface shielding [5]. Fractals are generated by diffusion limited agglomeration (DLA) and cluster-cluster agglomeration and compared to literature prior to proposing quantitative relationships between agglomerate structure and growth.

1. Teleki, A., M.C. Heine, F. Krumeich, M.K. Akhtar, S.E. Pratsinis, In-situ coating of flame-made TiO2 particles by nanosized SiO2 films, Langmuir, 24,12553-8 (2008).

2. A. Teleki, B. Buesser, M.C. Heine, F. Krumeich, M.K. Akhtar, S.E. Pratsinis, The role of gas-aerosol mixing during in-situ coating of flame-made titania particles, Ind. Eng. Chem. Res., 48, 85-92 (2009).

3. A. Teleki, M. Suter, P. Kidambi, O. Ergeneman, F. Krumeich, B.J. Nelson, S.E. Pratsinis, Hermetically-coated superparamagnetic Fe2O3 particles with SiO2 nanofilms, Chem. Mater., in press (2009).

4. Heine, M.C. and Pratsinis, S.E., Brownian coagulation at high concentration. Langmuir, 23(19), 9882-9890 (2007).

5. Xiong, Y. and Pratsinis, S.E., Formation of agglomerate particles by coagulation and sintering. 1. A 2-dimensional solution of the population balance equation. J. Aerosol. Sci., 24(3), 283-300 (1993).