Nanotech 2011

Ultrasonic Production of Nano-Size Dispersions and Emulsions

T. Hielscher
Hielscher Ultrasonics GmbH, DE

Keywords: ultrasonic dispersing, ultrasonic emulsifying, nano, nano-sized emulsions

Abstract:

Ultrasound is a well-established method for particle size reduction in dispersions and emulsions. Ultrasonic processors are used in the generation of nano-size material slurries, dispersions and emulsions because of the potential in the deagglomeration and reduction of primaries. These are the mechanical effects of ultrasonic cavitation. Ultrasound can also be used to influence chemical reactions by the cavitational energy. This is sonochemistry. As the market for nano-size materials grows, the demand for ultrasonic processes at production level increases. At this stage, energy efficiency becomes important. Since the energy is required per weight or volume of processed material, the process volume links directly to the equipment size required. Therefore, the optimization of the process efficiency is essential to reduce investment and operational costs. Furthermore is required to scale the lab and bench-top configurations to this final level without any variations in the process achievements. Scale up by power alone will not do this. Dispersing and Deagglomeration Dispersion by ultrasound is a consequence of microturbulences caused by fluctuation of pressure and cavitation. Investigations at different materials have demonstrated the considerable advantage of ultrasound when compared with other technologies, such as rotor-stator mixers or colloid mills. In particular for small matter from several nanometer to couple of microns, ultrasonic cavitation is very effective in breaking agglomerates, aggregates and even primaries. Emulsifying If a cavitational bubble implodes near the phase boundary of two immiscable liquids the resultant shock waves can provide a very efficient mixing. Ultrasonically generated emulsions – also nano-emulsions - are often more stable and require less, if any surfactant than those produced conventionally. By ultrasound produced emulsions show smaller droplet sizes within a narrow size distribution. Since ultrasound is fully controllable and adaptable by the choice of ampltude, pressure and temperature, sonication is an effective tool to obtain nano-size dispersions and emulsions.
 

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