Electric field assisted-unidirectional hybrid films of carbon nanotubes and liquid crystal polymer for light modulation

To develop stable polymer films which had high orientational ordering of carbon nanotube for polarization-dependent light modulator, we present a new concept for electric-field induced alignment of mesogenic carbon nanotubes (m-CNTs) in reactive mesogen host (RMS) fixed by ultraviolet (UV) polymerization. Covalent modification of m-CNTs was performed using structure-tailored mesogenic units [4-(6-hydroxyhexanolxy)-4’-carbonitrile, PCNOH] in esterification reaction based on 100–500 nm long CNTs shortened by acid oxidation cutting, confirmed through ¹H NMR, FT-IR, Raman and XPS spectroscopy. Dynamic orientation of m-CNTs in soft m-CNT/RMS composite without aggregates was observed on a large scale by polarized optical microscopy, in which m-CNTs aligns along the electric field direction. It was reasonable the mesogenic segments introduced onto m-CNTs weakened van der walls interactions between the nanotubes by increasing steric repulsion, and then effectively improved the favourable affinity of m-CNTs with RMS molecules. Direct UV-induced polymerization of RMS molecules stabilized the orientational ordering of m-CNTs confirmed by Raman spectroscopy, and the obtained film also exhibited anisotropic light absorption depending on the polarization direction of an incident light. The facile methodology described in this study to generate oriented films of m-CNTs-in-RMS broadened the scope of potential applications of modulator devices and versatile functional composites with anisotropic physical properties.