A uniform dispersion of CNTs in 3D-printable inks can enhance the properties of ink and enable new applications in various fields. Probe-type ultrasonication is a highly reliable dispersing technique to produce stable nanosuspensions of CNTs in polymers.

Efficient and Stable CNT Dispersion in Polymers due to Sonication

Carbon nanotubes (CNTs) are often dispersed in silicon oils for various applications due to their unique properties. The dispersion of CNTs in silicon oils can improve the mechanical, thermal, and electrical properties of the resulting materials. One such application is the fabrication of CNT-doped polymers for conductive 3D-printable inks, e.g., for the bio-based additive manufacturing of wearable tactile sensors, patient- specific tissue regeneration scaffolds, and flexible ECG and EEG electrodes.
In addition, CNTs dispersed in silicon oils can be used as conductive inks in electronic devices, such as flexible displays and sensors. The CNTs act as conductive pathways, allowing for the flow of electrical current.

Advantages of Ultrasonic CNT/Polymer Dispersion

Ultrasonication is a very efficient dispersing technique, which comes with several benefits. The advantages of ultrasonic dispersing of carbon nanotubes (CNTs) in polymers include:

General Protocol for the Ultrasonic Production of CNT/PDMS Composites

Ultrasonication is used for the dispersion of numerous nano-sized materials in polymers. A specific and commonly used application is the dispersion of carbon nanotubes (CNTs) in dimethylpolysiloxane (PDMS) using probe-type sonication. In order to disperse CNTs into the PDMS matrix, power ultrasound and the resulting effects of acoustic cavitation are used to detangle the nanotubes and mix them uniformly into a nanosuspension. Probe-type sonication is a powerful method for dispersing CNTs due to its ability to generate intense cavitation forces that can effectively break up and disperse agglomerated CNTs.
Ultrasonic dispersing is a simple processing step that requires no specific pre- or post-treatment. The ultrasonic equipment itself is safe and easy to operate.
The process of dispersion using probe-type sonication typically involves the following steps:

1. Preparation of the CNT-PDMS mixture: A predetermined amount of CNTs is added to the PDMS matrix and are pre-mixed using mechanical stirrer. Interestingly, by pre-dispersing CNTs in a solvent the electrical conductivity could be increased. Best results are achieved by tetrahydrofuran (THF), acetone or chloroform (sorted by best results).
2. Probe-type sonication: The mixture is subjected to probe-type sonication using a high-intensity ultrasonic probe that generates ultrasound waves with a frequency of typically approx. 20 kHz. Depending on the volume and formulation, sonication is typically carried out for several minutes to ensure complete dispersion of the CNTs.
3. Monitoring the dispersion: The dispersion of the CNTs is monitored using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), or UV-Vis spectroscopy. These techniques can be used to visualize the distribution of CNTs within the PDMS matrix and to ensure that the CNTs are uniformly dispersed.

In summary, probe-type sonication is a powerful method for dispersing CNTs in polymers such as PDMS due to its ability to generate intense cavitation forces that can effectively break up and disperse agglomerated CNTs.

Case Studies of Ultrasonic Fabrication of CNT/Polymer Composites

The dispersion of nanotubes and other carbon-based nanomaterials using probe-type ultrasonication has been extensively researched and has been subsequently implemented into industrial production. Below, we present a few research studies, which demonstrate the exceptional efficiency of ultrasonic nanotube dispersion.

Ultrasonic dispersion of CNTs in PDMS for wearable sensors

Del Bosque et al. (2022) compared three-roll milling and sonication for their effectiveness of CNT dispersion. The analysis of the dispersion procedure of nanoparticles into the polymer matrix shows that the ultrasonication technique provides a higher electrical sensitivity in comparison to three-roll milling due to the higher homogeneity of the CNT distribution induced by the cavitation forces. Testing various CNT loadings, the percolation threshold of the CNT-PDMS system, that is, the critical CNT content in which it becomes electrically conductive, was found to be 0.4 wt% CNT. Multi-Wall Carbon Nanotubes (MWCNTs) were dispersed by ultrasonication using the Hielscher ultrasonicator UP400ST (see picture left) at 0.5 pulse cycles and 50 % amplitude for 2h. The effects of ultrasonic dispersing over the course of sonication time are shown in the picture below.
Based on this analysis, the optimum conditions for the manufacturing of the wearable sensors were selected as 0.4 wt.% CNT by means of an ultrasonication process. In this regard, an analysis of the electrical response under consecutive load cycles showed a high robustness of the developed sensors, without any presence of damage at 2%, 5%, and 10% strain, which make these sensors reliable for monitoring medium strain.

Ultrasonic dispersion of MWCNTs in PDMS using the ultrasonicator UP400St at various sonication times.
(Study and image: ©del Bosque et al., 2022)

High-Performance Ultrasonic Dispersing Equipment for CNT/Polymer Nanocomposites

Hielscher Ultrasonics manufacturers high-power ultrasound probes for demanding dispersing applications in lab, bench-top and industry. Hielscher Ultrasonics dispersers provide efficient and precise homogenization and dispersion of nanomaterials in solvents, polymers and composites.
With their advanced ultrasonic technology, these dispersers offer a quick and easy solution for achieving uniform particle size distribution, stable dispersions, and/or nanoparticle functionalization.
By reducing processing time and minimizing energy consumption, ultrasonic probe dispersers can improve productivity and reduce operational costs for businesses across a variety of industries.
Hielscher ultrasonicators can also be customized to suit specific requirements, with options for a range of probe sizes, booster horns, power levels, and flow cells, making them versatile and adaptable to various nano-formulations and volumes.
Overall, ultrasonic probe dispersers are an excellent investment for laboratories and industries looking to optimize their nanomaterial processing workflows and achieve consistent, reliable results.

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are reliably handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

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