Ultrasonic Deagglomeration of Silica Nanoparticles

Silica nanoparticles such as fumed silica (e.g. Aerosil) are a widely used additive in various industries. In order to obtain fully functional nanosilica with the desired material characteristics, the silica nano-particles must be deagglomerated and distributed as single-dispersed particles. Ultrasonic deagglomeration has been proven to be a highly efficient and reliable technique to distribute nanosilica uniformly as single-dispersed particles in a suspension.

Nanosilica – Characteristics and Applications

Silica (SiO₂) and especially silica nanoparticles (Si-NPs) are common additives in many industries. Nano-sized silica particles offer a very large surface area and express unique particle characteristics, which are utilized in many industries for various purposes. For instance, the unique material properties of nano-sized SiO₂ are applied in order to reinforce (nano-)composites, concrete and other materials. Examples are nanosilica-based coatings that offers fireproof properties or glass coated with nanosilica that gains thereby antireflective properties. In the building and construction industry, silica fume (microsilica) and nanosilica are used as highly pozzolanic material that is used to enhance workability as well as mechanical and durability properties of concrete. When silica fume and nanosilica are compared, the nano-structured SiO₂ pozzolan is more active in early stage than silica fume since nanosilica offers a significantly larger specific surface area and fineness. The larger surface area offers more sites to react with the concrete and contributes specifically to an improved concrete microstructure by acting as a nucleus. Gas permeability, an indicator for durability of concrete, is improved in concrete that is reinforced with nano-silica in comparison to concrete containing traditional silica fume.
In biomedicine and life science, SiO₂ nanoparticles are widely investigated for different applications since the high surface area, excellent biocompatibility, and tunable pore size of nanosilica offers a wide range of novel applications including drug delivery and theranostics.

The chart shows the particle size distribution of nano-silica before (green curve) and after (red curve) ultrasonic dispersion.

Ultrasonic Deagglomeration and Dispersion of Nano-Silica

The working principle of ultrasonic deagglomeration and dispersion is based on the effects of ultrasonically generated cavitation, scientifically known as acoustic cavitation. The application of high-power, low-frequency ultrasound in liquids or slurries can cause acoustic cavitation and thereby extreme conditions, which occur locally as very high pressures and temperatures, and microstreaming with liquid jets of up to 280m/s. These intense physical and mechanical effects of ultrasonic cavitation cause erosion at the particle surface as well as shattering of particles via inter-particle collision. These intense forces of ultrasonic / acoustic cavitation make sonication a highly efficient and reliable method for the deagglomeration and dispersion of nano-sized particles auch as nano-silica, nanotubes and other nano materials.

Particle size distribution of ultrasonically deagglomerated nano-silica (using the Hielscher UP400St ultrasonicator) in water of (a) 1 wt%, (b) 2 wt%, (c) 5 wt%, and (d) 10 wt% Aerosil 200 at different time intervals.
Study and graphs: Vikash 2020.

Ultrasonic Processing of Silica with High Solid Concentrations and in Viscous Liquids

Dispersing nanoparticles at low concentrations is already a challenging since chemical bonding forces such as ionic bonds, covalent bonds, hydrogen bonds, and van der Waals interactions must be overcome. With increasing concentration of nanoparticles, e.g., nano-silica particles, the chemical interaction between the nanoparticles is significantly increased, too. This means a powerful dispersion technique is essential in order to obtain good, long-term stable dispersion results. Ultrasonic dispersers are used as reliable and highly efficacious dispersion method, which are easily capable to process slurries with high viscosities and even pastes with very high solid concentrations. The capability to process slurries with high solid loads of nano-particles turns ultrasonication into the preferred dispersing technology for nano-materials.
Hielscher industrial ultrasonicators can process your slurry or paste in an continuous in-line reactor as long as it can be fed via a pump.

Ultrasonic Production of Silica Nanofluids

Modragon et al. (2012) prepared silica nanofluids prepared by dispersing silica nanoparticles in distilled water using the probe-type ultrasonicator UP400S. In order to produce stable silica nanofluids with a certain solid content (i.e., 20%), with low viscosity and like liquid behaviour, consist in a high energy treatment with an ultrasound probe for 5 minutes, basic media (pH values higher than 7) and no salt addition. The ultrasonic dispersion resulted in nanofluids with low viscosity. The ultrasonically prepared nanofluids behaved like liquid and were prepared with 20% of solid loading within a very short time thanks to the good dispersion achieved with sonication.
“Of all the dispersion methods available, dispersion with ultrasonic probes has been confirmed as the most effective one.“ (Modragon et al., 2012)
Petzold et al. (2009) came to the same conclusion for deagglomeration of Aerosil powder finding that the ultrasonic probe is the most effective dispersion system due to the highly focused energy applied.

Ultrasonicators for Deagglomeration and Dispersion of Silica Nanoparticles

When nano-silica is used in industrial applications, research or material science, the dry silica powder imust be incorporated into a liquid phase. Nano-silica dispersion requires a reliable and effective dispersing technique, which applies enough energy to deagglomerate the single silica particles. Ultrasonicators are well known as powerful and reliable dispersers, therefore used to deagglomerate and distribute various materials such as silica, nanotubes, graphene, minerals and many other materials homogeneously into a liquid phase.

Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic dispersers for any kind of homogenization and deagglomeration applications. When it comes to the production of nano-dispersions, precise sonication control and a reliable ultrasonic treatment of the nanoparticle suspension are essential in order to obtain high-performance products.
Hielscher Ultrasonics’ processors give you full control over all important processing parameters such as energy input, ultrasonic intensity, amplitude, pressure, temperature and retention time. Thereby, you can adjust the parameters to optimized conditions, which leads subsequently to high-quality nano-dispersion such as nanosilica slurries.
For any volume / capacity: Hielscher offers ultrasonicators and a broad portfolio of accessories. This allows for the configuration of the ideal ultrasonic system for your application and production capacity. From small vials containing a few millilitres to high volume streams of thousands of gallons per hour, Hielscher offers the suitable ultrasonic solution for your process.
Robustness: Our ultrasonic systems are robust and reliable. All Hielscher ultrasonicators are built for 24/7/365 operation and require very little maintenance.
User-friendliness: Elaborated software of our ultrasonic devices allows the pre-selection and saving of sonication settings for a simple and reliable sonication. The intuitive menu is easily accessible via a digital coloured touch-display. The remote browser control allows you to operate and monitor via any internet browser. Automatic data recording saves the process parameters of any sonication run on a built-in SD-card.
Excellent energy efficiency: When compared to alternative dispersion technologies, Hielscher ultrasonicators excel with outstanding energy efficiency and superior results in particle size distribution.

The chart shows the significant advantage of ultrasonic dispersion of silica with the Hielscher UIP1000 when compared to an ultra-turrax. Ultrasonication requires less energy and achieves drastically smaller particles size of the silica.

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