Infiltration of direct-spun carbon nanotube articles

A key step towards realizing the promise of macroscopic carbon nanotube (CNT) articles in high-performance structural applications is polymer infiltration into the porous CNT structure, which improves stress transfer and promotes long-term material integrity. However, infiltration is often found to be sub-optimal - a significant impediment to the scaling and adoption of CNT-article composites that has thus far received little systematic attention. In this study, a unique combination of inverse gas chromatography (IGC) and a statistical thermodynamic model is used to accurately quantify the energetic driving force for infiltration into CNT articles for the first time. This is measured to have a very low value. Using gas chromatography-mass spectroscopy, IGC analysis and electron microscopy, this low energy is found to result from near-complete surface coverage by non-graphitic pyrolysis byproducts. The surface energy is improved by plasma treatment as confirmed by IGC analysis. The effects of the surface treatment and modifications to the porous structure on the infiltration rate of model liquids are studied by optical imaging. Accurate surface energy measurements and image analysis are coupled to shed light on the critical parameters in these CNT articles that dictate the infiltration physics, which can be tuned to maximize the rate and extent of space filling.