Hielscher - Ultrasound Technology

Dispersion and deagglomeration of nanopowders and the reduction of primary particles in micron and submicron range is required in many processes in the pharmaceutical, chemical, and paint and ink industries. Other nanoscale particles, such as biodegradable micro- and nanospheres are very potent drug and antigen delivery systems with inherent potential for drug and antigen targeting.

Nanomaterials, such as metal oxides, nanoclays and carbon nanotubes tend to be agglomerated when being mixed into a liquid. Therefore effective means of deagglomerating and dispersing are required to overcome the bonding forces after wettening the micron-powder or nano-powder. For this application, ultrasound has proven to be more effective than many other devices, such as rotor stator mixers (e.g. ultra turrax), piston homogenizers, gear pumps or wet grinding methods, such as beat mills, colloid mills and ball mills. Dispersion by ultrasound is a consequence of microturbulences caused by fluctuation of pressure and cavitation . Investigations at different materials, such as aqueous solutions of nanoparticulate siliciumdioxid powder and spray frozen agglomerates with a variable solid content have demonstrated the considerable advantage of ultrasound when compared with other technologies.

Micron-size and nano-size materials down to the size of several nanometers are favored for many applications due to their large surface area. An increase in available surface area can result in the increase of the reactivity of reagents and catalysts. The ultrasonic breakup of the agglomerate structures in aqueous and non-aqueous suspensions allows to utilize the full potential of such materials. Ultrasound does so on a more energy and cost effective basis. In addition to that, ultrasonic systems can be run at fairly high concentrations. For example for silica the breakage rate was found to be independent of the solid concentration up to 50% by weight.

Ultrasonic processors and flow cells for deagglomeration and dispersion are available for laboratory and production level. The industrial systems can easily be retrofitted to work inline. For the research and for the testing of this process as well as for many sonochemical processes we recommend our laboratory devices or the UIP1000 set.

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Literature:

• Pohl, M., Schubert, H.: Dispersion and deagglomeration of nanoparticles in aqueous solutions, in: Partec 2004.
• Behrend, O., Schubert, H.: Influence of hydrostatic pressure and gas content on continuous ultrasound emulsification, in: Ultrasonics Sonochemistry 8 (2001) 271-276.
• Freitas, S., Hielscher, G., Merkle, H. P., Gander, B.: The Fastest and Most Simple Method For Producing Biodegradable Nanospheres, in: Swiss Society of Biomaterials.