Effects of CNTs in polymer nanocomposite pillars fabricated through Two-Photon Polymerization

Abstract

In recent decades, advancements in the synthesis and manufacturing of carbon nanomaterials such as carbon nanotubes (CNTs) have made such materials excellent candidates for reinforcing polymers, providing substantial contributions to the field of polymer nanocomposites. CNTs have been widely used in areas such as electronic devices, automotive, and the aerospace sectors to name a few. They offer excellent electrical, mechanical, and thermal properties making it a strong candidate as a nanofiller for polymer composites. Combining this material with the emergence of direct laser writing using 2-photon polymerization (2PP), we can now begin studying and understanding nanostructured nanocomposites. 2PP enables us the design freedom to create niche structures and provide theoretically unlimited component complexity. Therefore, opening the area of nano-architected materials.In this work, printability and mechanical behavior of micro- and nano-pillars made from custom di(trimethylolpropane) tetra-acrylate polymer and 0.004wt% functionalized-CNT will be investigated. Pillars tested had an aspect ratio of 3 where diameters were targeted at 10um, 1um, 600nm, 500nm, 400nm and 300nm. For printability, parameter sweeps were conducted to determine optimal print parameters. Parallel to this, a post-processing study observed the influence of UV exposure and drying options on pillar geometry. As for mechanical testing, micro- compression testing was conducted on all pillars. In particular, size effects in pure polymer pillar structures fabricated via 2PP and effects of CNTs on the mechanical properties of polymer nanocomposites from micro-compression testing are targeted. Our findings demonstrate that CNTs enhanced mechanical properties of pillars with a diameter of 10um compared to their pure polymer counterparts. Though when investigating pillars with diameters 1um and below, the fabricated structures appear instable to satisfy the conditions required for compression testing, thereby prohibiting systematic conclusions for the case of the composites. On the contrary, for the pure polymer a strengthening and stiffening was observed for decreasing pillar diameters, confirming size-effects previously reported for amorphous thermoplastics.