A brush-coating approach to achieve anisotropic optical film via field-induced stretching of carbon nanotube clusters in a reactive mesogen

We present a novel brush coating method for fabricating a coatable polarizer that utilizes a mixture of functionalized single-walled carbon nanotubes (h-SWCNTs) grafted with carboxyl and hydroxyl groups and a reactive mesogen (RM), which possess a long-range orientational ordering of their rod-shaped molecules with photo-sensitive functional groups. The h-SWCNTs are shortened to a length of around 150 nm by an acid sonochemical oxidation process and then dispersed in an RM solution. The brush-coated thin layer initially consists of h-SWCNT clusters, but applying an in-plane electric field induces large-scale stretching of these along the field direction, after which the layer is photo-polymerized by ultraviolet irradiation to form a film embedding the stretched nanotubes. The uniaxially aligned carbon nanotubes (CNTs) produce a broadband absorption spectrum that enables the film to exhibit an optical anisotropic property that absorbs incident light from the ultraviolet to the visible spectrum selectively depending on the polarization direction, thus acting as a coatable CNT polarizer. The dispersibility and elongation of h-SWCNT clusters induced by applying the electric field, as well as the anisotropic light-absorption properties of the h-SWCNT film, are investigated.