High Pressure Dispersion of Agglomerates
Nanoparticles constitute the disperse phase in nanocomposites improving optical, mechanical, thermal or handling properties of coatings or bulk materials, i.e. dental materials. Synthesis of nanocomposites often requires re-dispersion of dry particles in an aqueous or monomer solution. Flame technology often leads to agglomerated nanoparticles (e.g. fumed silica and alumina). These particles may be held together physically by van der Waals forces (soft agglomerates) or by stronger chemical or sintering bonds (hard agglomerates). The degree of agglomeration strongly affects particle performance and depends on process conditions, in particular on temperature profile and residence time. Liquid dispersion of agglomerates requires the exertion of high stresses on the constituent particles.
This study investigates high pressure dispersion and fragmentation of flame-made agglomerates in liquids. A high pressure dispersion apparatus for abrasive dispersions has been developed. It is used to apply very high stresses on the particles thus being able to break-up physical bonds as well as weak sinter necks. Here silica particles are produced in a co-flow diffusion flame reactor. The particle generation is controlled by the reactant flow rates leading to samples with different particle size and degree of agglomeration. Soft agglomerates with physical bonding break-up by high hydrodynamic stresses. Thus hard agglomerate diameters of flame-synthesized particles could be measured by liquid dispersion as characterized by dynamic light scattering.
Recent, relevant references:
- Mueller, R., H. K. Kammler, S. E. Pratsinis, A. Vital, G. Beaucage, and P. Burtscher, “Non-agglomerated dry silica nanoparticles,” Powder Technol. 140, 40 (2004).
- Tsantilis, S., and S. E. Pratsinis, “Soft- and hard-agglomerate aerosols made at high temperatures,” Langmuir 20, 5933 (2004).
- Wengeler, R., A. Teleki, M. Vetter, S. E. Pratsinis, and H. Nirschl, “High pressure liquid dispersion and fragmentation of flame-made silica agglomerates,” Langmuir 22, 4928 (2006).