Ultrasound alignment of a high weight fraction of carbon nanotubes in a polymer matrix

This research introduces a new process to fabricate polymer nanocomposite materials reinforced with an ultra-high weight fraction of aligned carbon nanotubes (CNTs). This process is based on ultrasound directed self-assembly, which employs the force associated with a standing ultrasound wave to concentrate and align the carbon nanotubes in a user-specified pattern. In contrast with existing processes, which typically limit fabricating nanocomposite materials with a CNT weight fraction on the order of 1 weight percent (wt.%), polymer nanocomposite materials were fabricated to contain a weight fraction of aligned CNTs in excess of 10 wt. %. The fabrication process, dispersion of CNTs in the polymer matrix, appropriate acoustic wave propagation velocity in the matrix material, and degradation of polymer mechanical properties from exposure to ultrasound stimulation are described. The mechanical properties of these polymer nanocomposite specimens were experimentally measured and it was found that the ultrasound alignment process resulted in specimens that displayed a significant increase in ultimate tensile strength, Young’s modulus, and moduli of resilience and toughness, compared to specimens including polymer nanocomposite materials with randomly oriented CNTs, and “processed polymer”. The research demonstrates that by combining ultrasound alignment with microwave radiation exposure, the Young’s modulus and ultimate tensile strength of the polymer nanocomposite material is further enhanced. Specimens were affected differently by microwave radiation exposure, depending on the type of alignment and dispersion used to create the specimen. These observations may guide further optimization of the process.