Interface enhancement and tunable electromagnetic properties of vertically aligned N-doped carbon nanotube arrays/polydimethylsiloxane composites

In this study, we investigated the impact of nitrogen doping of vertically-aligned carbon nanotube (VACNT) arrays on their interaction with an elastomeric polymer. Specifically, we synthesized undoped and N-doped VACNT (N-VACNT) arrays and examined the direct current conductivity, THz responses, and elastic properties of their polydimethylsiloxane (PDMS)-impregnated composites. Structural diagnostics confirmed that incorporating approximately 1 at% nitrogen yielded mechanically stiff N-CNTs with superior ordering within the array compared to undoped VACNT array. This structural enhancement led to significantly improved conductivity and THz shielding efficiency in N-VACNT/PDMS composites. For instance, a 70 µm-thick N-VACNT array impregnated with PDMS achieved a transmittance of 10⁻³, comparable with the value for an impregnated 200 µm-thick undoped array. Despite exhibiting lower ultimate tensile strains (40% for N-VACNT/PDMS vs. 70% for VACNT/PDMS), the N-VACNT/PDMS composites provided a broader conductivity and transmittance modulation window with less deformation. Under initial tension, undoped and N-doped PDMS-impregnated arrays showed distinct electrical and THz behaviors. While VACNT/PDMS composites suffered from permanent conductivity loss and material rearrangement upon initial stretching, N-VACNT/PDMS composites displayed fully reversible DC conductivity and a stable THz response over repeated stretch-release cycles. Density functional theory calculations revealed that graphite-like and pyridine-like nitrogen atoms in the nanotube walls enhance the adsorption of PDMS chains. Stronger interfacial bonding, combined with the superior ordering of stiff N-VACNTs, enables complete recovery of the N-VACNT/PDMS composite structure and its electromagnetic response after deformation. These results highlight the key role of nitrogen doping in tailoring both the nanoscale structure and performance of CNT elastomer composites. The N VACNT/PDMS system thus emerges as a leading candidate for stretchable THz components and other applications requiring stable, reversible electromechanical response, paving the way for advanced tunable sensors and functional composites.