Characteristics of ultrasonic dispersion of carbon nanotubes aided by antifoam

Ultrasonication is a common technique applied to disperse carbon nanotubes (CNTs) in liquid media. Due to poor wetting, air layers and gas bubbles tend to be trapped on the CNT surfaces or the interstices of bundles. Also, surfactants used to stabilize CNT dispersions often foam heavily. Because the incoming ultrasonic wave is reflected at the air–liquid interface, these air layers and foams prevent the wave from reaching the CNT surfaces. Additions of antifoam agents to the dispersing liquid are shown to improve ultrasonic dispersion efficiency of CNTs. In some cases, the dispersed amount is increased more than 20 times. Resonance Raman spectroscopy is used to study the mechanism of improvement, with the result that antifoam helps ultrasonic to break thick bundles into many thin bundles, rather than freeing an individual CNT at a time, which is the case when surfactants are used without antifoam.