Sonication of CNTs are normally done for dispersing them uniformly in a fluid so that the subsequent sample preparation becomes easier. e.g. TEM sample preparation. Sonication normally does not break individual CNTs but it may break lumps of CNTs along with amorphous Carbon. However, breaking of lumps might generate defects in CNTs. But the defects should not be too much.

I can't speak to the issue of whether or not CNTs are broken, but we have had good success at dispersing SWCNTs in acrylate-functional systems with simple sonication. UV-Vis spectroscopic studies indicated good exfoliation of the SWCNT "ropes" after sonication.

It certainly effects solubility and can lead to defects and breakage

"Ultrasound-Assisted SWNTs Dispersion: Effects of Sonication Parameters and Solvent Properties",

Qiaohuan Cheng, Sourabhi Debnath, Elizabeth Gregan and Hugh J. Byrne,

J. Phys. Chem. C, 114, 8821-8827 (2010)

To add,

As the CNTs tend to form aggregates, when one wants to separate them into individual CNTs for further characterization or fabrication ultrasonication helps in breaking the aggregates. In ultrasonication it is the frequency which makes CNTs or any other nano material separate in a medium of solvents.

@ Shubrajit, I have found this paper which may help you in someway. Yan Yan Huang and Eugene M. Terentjev, Dispersion of Carbon Nanotubes: Mixing, Sonication, Stabilization, and Composite Properties,Polymers 2012, 4, 275-295; doi:10.3390/polym4010275.

Also keep in mind that (ultra)sonication just describes a technique but not the parameters used. Be aware that there are various sonication devices with vastly different effects on your CNTs. On the one hand ultrasonic baths are rather used for cleaning purposes and often operate at ~40kHz and have a power consumption of some ten Watts for the sonication (the total power consumption of the device might be considerably higher if the bath is heatable). On the other hand there are ultrasonic tips (or fingers) whose primary purpose is to disperse particles in a solution. The latter may operate at hundreds of watts sonication power (adjustable) and is more powerful. The energy transfer from the tip to the solution is direct, meaning that CNTs can be in very close proximity to the sonication source (different from the sonication bath were the sonication is usually damped by a water bath and a glass baker wall containing your sample). Thus the sonication tip is more powerful in terms of dispersing and exfoliating CNT ropes or agglomerates but is has also been reported to be a method to cut CNTs.

In agreement with the answer of the others I experienced no substantial CNT cleavage in an average sonication bath (45kHz, 80W), even for prolonged sonication times.

Dear Matthias . Thank you for your kind reply. you have mentioned that with tip sonication we can cut CNTs , can you please specify whether they are cut along their perpendicular axis or parallell axis. or in other terms are the cnts sheared???upto what length can a cnt be cut?

Dear Shubrajit,

according to my knowledge the CNTs are cut perpendicular to the longitudinal axis under intense sonication. I am not aware if there is length limit.

I would guess there are two mechanism possible for cleavage. The first is energy transfer by cavitation, which should impose no lower limit on the lowest size, since you can think of it as an implosion unloading its energy arbitrarily. If you are interested in the mechanism you can consider: The Journal of Physical Chemistry C, Vol. 113, No. 48. (3 December 2009), pp. 20599-20605.

The second would be energy transfer by the wave nature of the sonication process. But if you estimate the wavelength of the water wave (sonic velocity in water (1497 m/s)) which gives 3cm for a 50kHz sonic transducer, the latter can be excluded as a method of (resonant) energy transfer since most CNTs are shorter than the wavelength/2(=1.5cm).

If you are interested to get short CNT you may try the chemical method reported in J. Am. Chem. Soc., Vol. 128, No. 32. (21 July 2006). pp. 10568-10571

If your are interested in a longitundinal cutting to yield small graphene ribbons you may want to try a chemical method reported in Nature 458, 872-876.

Let me know if this helps.

Like what it does with other types of particles, bit for CNTs it is more critical, because they form stable bundles due to strong van der Waals interactions. But sonication is not destructive to the CNTs.

Dear mathias thankx a ton for your answers

Simply, It depends on the sonication frequency and duration. For MWCNTs, sonication is destructive in most of the cases. Also, the effect of sonication depends on the degree of graphitization of your sample (check with Raman results).

Simple sonication in our labs in UV-polymerizable, acrylate-functional monomer mixtures produced dispersions with obvious van hove singularities in the UV-Vis spectra.  This is good indication of exfoliation of SWNTs.  Raman data were not collected for these samples.

Hi, in my lab we have a probe sonicator and recently another group started using it to disperse carbon nanotubes, since then I've seen increasing damage of the tip. Could the nanotubes be the cause? Or maybe they are using it at higher % than the tip limit?

no - depending on quality of tip it will be damaged over time due to sonication power. This process will speed-up over time.

Ok, thanks!