Transparent and flexible films of horizontally aligned carbon nanotube/polyimide composites with highly anisotropic mechanical, thermal, and electrical properties

Flexible anisotropic films manufactured from one-dimensional aligned nanomaterials can be potentially used in electronic skin and thermal interface applications due to their anisotropic properties. However, high anisotropy also makes the fabrication of aligned polymeric composites with a highly ordered structure and good interface properties very problematic. In this work, transparent, flexible, and robust anisotropic films containing aniline-grafted horizontally aligned carbon nanotube (G−HACNT)/polyimide (PI) composites have been synthesized. The obtained uniform G−HACNT/PI composite films are characterized by a variety of excellent anisotropic properties. Thus, the film electrical (σ) and thermal (κ) conductivities in the longitudinal direction are one order of magnitude higher than the corresponding values measured in the transverse direction (σ//:σ⊥ = 15.3, κ///κ⊥ = 10.1). Furthermore, the tensile strength in the longitudinal direction exceeds that in the transverse direction by 52.9%. The high anisotropy of the flexible films (observed even at 200 °C) with extremely low contents of G−HACNTs (less than 0.1 wt%) originates from the well-aligned nanostructures and preferentially oriented crystalline PI chains. Hence, the flexible and robust G−HACNT/PI composite films with uniformly aligned structures pave the way for fabricating in-plane anisotropic polymeric nanocomposites by controlling interactions between the nanotube and PI components.