Ultrasonic Dispersing and Deagglomeration

The dispersing and deagglomeration of solids into liquids is an important application of power ultrasound and probe-type sonicators. Ultrasonic cavitation generates extraordinarily high shear that breaks particle agglomerates into single dispersed particles. Due to its locally focused high shear forces, sonication is ideal to produce mircon- and nano-sized dispersions for experimentation, research and development, and of course for industrial production.

The mixing of powders into liquids is a common step in the formulation of various products, such as paint, ink, cosmetics, beverages, hydrogels, or polishing media. The individual particles are held together by attraction forces of various physical and chemical nature, including van der Waals forces and liquid surface tension. This effect is stronger for higher viscosity liquids, such as polymers or resins. The attraction forces must be overcome on order to deagglomerate and disperse the particles into liquid media. Read below why ultrasonic homogenizers are the superior dispersing equipment for the dispersion of submicron- and nano-sized particles in lab and industry.

Ultrasonic Dispersing of Solids into Liquids

The working principle of ultrasonic homogenizers is based on the phenomenon of acoustic cavitation. Acoustic cavitation is known to create intense physical forces, including very strong shear forces. The application of mechanical stress breaks the particle agglomerates apart. Also, liquid is pressed between the particles.
Whilst for the dispersing of powders into liquids, various technologies such as high pressure homogenizers, agitator bead mills, impinging jet mills and rotor-stator-mixer are commercially available. However ultrasonic dispersers have significant advantages. Read below how ultrasonic dispersion works and what the advantages of ultrasonic disperse are.

 

 

The Working Principle of Ultrasonic Cavitation and Dispersion

During sonication, high-frequency sound waves create alternating areas of compression and rarefaction in the liquid medium. As the sound waves pass through the medium, they create bubbles that rapidly expand and then violently collapse. This process is called acoustic cavitation. The collapse of the bubbles generates high-pressure shock waves, microjets, and shearing forces that can break down larger particles and agglomerates into smaller particles. In ultrasonic dispersion processes, the particles themselves in the dispersion function as milling medium. Accelerated by the shear forces of ultrasonic cavitation, the particles collide with each other and shatter into tiny fragments. Since no beads or pearls are added to the ultrasonically treated dispersion, the time-consuming and labour-intense separation and cleaning of milling media as well as contamination are completely avoided.
This makes sonication so effective in dispersing and deagglomerating particles, even those that are difficult to break down with other methods. This results in a more uniform distribution of particles, leading to improved product quality and performance.
In addition, sonication can easily handle, disperse and synthesize nanomaterials such as nanospheres, nanocrystals, nanosheets, nanofibres, nanowires, core-shell particles and other complex structures.
Furthermore, sonication can be performed in a relatively short time frame, which is a major advantage over other dispersion techniques.

Advantages of Ultrasonic Dispersers over Alternative Mixing Technologies

Ultrasonic dispersers offer several advantages over alternative mixing technologies such as high-pressure homogenizers, bead milling or rotor-stator mixing. Some of the most prominent advantages include:

• Improved Particle Size Reduction: Ultrasonic dispersers can effectively reduce particle sizes to the nanometer range, which is not possible with many other mixing technologies. This makes them ideal for applications where a fine particle size is critical.
• Faster Mixing: Ultrasonic dispersers can mix and disperse materials faster than many other technologies, which saves time and increases productivity.
• No Contamination: Ultrasonic dispersers do not require the use of milling media auch as beads or pearls, which contaminate the dispersion by abrasion.
• Better Product Quality: Ultrasonic dispersers can produce more uniform mixtures and suspensions, resulting in better product quality and consistency. Especially in flow-through mode, the dispersion slurry passes the ultrasonic cavitation zone in a highly controlled manner ensuring a very uniform treatment.
• Lower Energy Consumption: Ultrasonic dispersers typically require less energy than other technologies, which reduces operating costs.
• Versatility: Ultrasonic dispersers can be used for a wide range of applications, including homogenization, emulsification, dispersion, and deagglomeration. They can also handle a variety of materials, including abrasive materials, fibres, corrosive liquids, and even gases.

Due to these process advantages as well as reliability and simple operation, ultrasonic dispersers outcompete alternative mixing technologies, making them a popular choice for many industrial applications.

Ultrasonic Dispersing and Deagglomeration in Any Scale

Hielscher offers ultrasonic devices for the dispersing and deagglomeration of any volume for batch or inline processing. Ultrasonic laboratory devices are used for volumes from 1.5mL to approx. 2L. Industrial ultrasonic devices are used in the process development and production for batches from 0.5 to approx 2000L or flow rates from 0.1L to 20m³ per hour.

Hielscher Ultrasonics industrial ultrasonic processors can deliver very high amplitudes thereby reliably dispersing and milling particles to nano-scale. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Advantages of Ultrasonic Dispersion: Easy to Scale Up

Different from other dispersing technologies, ultrasonication can be scaled up easily from lab to production size. Laboratory tests will allow to select the required equipment size accurately. When used in final scale, the process results are identical to the lab results.

Ultrasonicators: Robust and Easy to Clean

Ultrasonic power is transmitted into the liquid via a sonotrode. This is a typically rotary symmetric part, that is machined from solid aircraft quality titanium. This is also the only moving / vibrating wetted part. It is the only part, that is subject to wear and it can be easily replaced within minutes. Oscillation-decoupling flanges allow to mount the sonotrode into open or closed pressurizable containers or flow cells in any orientation. No bearings are needed. All other wetted parts are generally made of stainless steel. Flow cell reactors have simple geometries and can be easily disassembled and cleaned, e.g. by flushing and wiping out. There are no small orifices or hidden corners.

Ultrasonic Cleaner in Place

Ultrasound is well known for its cleaning applications, such a surface, part cleaning. The ultrasonic intensity used for dispersing applications is much higher than for typical ultrasonic cleaning. When it comes to the cleaning of the wetted parts of the ultrasonic device, the ultrasonic power can be used to assist cleaning during flushing and rinsing, as the ultrasonic / acoustic cavitation removes particles and liquid residues from the sonotrode and from the flow cell walls.

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Literature / References

• Brad W. Zeiger; Kenneth S. Suslick (2011): Sonofragmentation of Molecular Crystals. J. Am. Chem. Soc. 2011, 133, 37, 14530–14533.
• Poinern G.E., Brundavanam R., Thi-Le X., Djordjevic S., Prokic M., Fawcett D. (2011): Thermal and ultrasonic influence in the formation of nanometer scale hydroxyapatite bio-ceramic. Int J Nanomedicine. 2011; 6: 2083–2095.
• László Vanyorek, Dávid Kiss, Ádám Prekob, Béla Fiser, Attila Potyka, Géza Németh, László Kuzsela, Dirk Drees, Attila Trohák, Béla Viskolcz (2019): Application of nitrogen doped bamboo-like carbon nanotube for development of electrically conductive lubricants. Journal of Materials Research and Technology, Volume 8, Issue 3, 2019. 3244-3250.
• Adam K. Budniak, Niall A. Killilea, Szymon J. Zelewski, Mykhailo Sytnyk, Yaron Kauffmann, Yaron Amouyal, Robert Kudrawiec, Wolfgang Heiss, Efrat Lifshitz (2020): Exfoliated CrPS4 with Promising Photoconductivity. Small Vol.16, Issue1. January 9, 2020.