Plant-Derived Cellulose Nanocrystals as Pre-alignment Layer for Ferroelectric Mesogens in Display Applications

Abstract

The alignment of mesogens is a critical determinant of the efficacy of liquid crystal display (LCD) devices. Conventional LCDs utilize the rubbed polyimide technique for mesogenic alignment on substrates, which is prone to static charges and impurities that can degrade device performance. Herein, we introduce an innovative bio-based environmental benign pre-alignment layer for LCDs by employing cellulose nanocrystals (CNC) derived from plant sources for the first time. Leveraging the self-assembling properties of CNC, thin films were fabricated on indium tin oxide (ITO) coated glass substrates using the evaporation-induced vertical deposition technique. The surface morphology of the prepared CNC layer was characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and profilometry. In addition, a systematic comparison on the surface energies of the developed CNC pre-alignment layer against other surfaces such as bare ITO-glass, nylon-coated on ITO-glass, and rubbed polyimide surface on ITO-glass were conducted. Further, the alignment of ferroelectric mesogens (ZLI 3654) were evaluated using the LC cells fabricated with the CNC pre-alignment layer and compared with the conventional devices. It is seen that the augmented surface energy of the self-assembled CNC layer on ITO coated glass enhances adhesive properties, leading to a robust mesogenic alignment. The quality of mesogenic alignment over CNC layers and the resultant device performance is intricately tied to the concentration of the CNC coating. Comparative analyses with conventional display devices reveal that the CNC-aligned device exhibits electro-optical performance par with its traditional counterpart, all while maintaining optical transparency. This investigation delves into the fundamental aspects of mesogenic alignment over CNC layers, offering insights for developing advanced LCD devices through a rubbing-free, environmental benign, and facile alignment technique.