Vanadium Dioxide Nanoparticle Doped Polyimide Hybrid Alignment Layers for Flexible Liquid Crystal Displays

In this paper, a flexible liquid crystal display (LCD) is developed by applying hybrid alignment layers made of vanadium dioxide (VO₂) nanoparticles and homeotropic-polyimide (h-PI) onto colorless plastic substrates, and the proposed hybrid thin layers with randomly embedded agglomerated VO₂ nanoparticles exhibit a transparency over 85% at 550 nm including the substrate and a strong surface irregularity. After rubbing, liquid crystals (LCs) are vertically aligned between the hybrid thin layers with a tilt angle of ∼90°, and due to the significant surface plasmon polariton (SPP) of VO₂ nanoparticles, the switch of LCs under the external electrical field has been remarkably accelerated. The operating voltage to switch LCs in a 5 μm cell assembled using a pair of 0.5% VO₂ nanoparticle doped h-PI hybrid alignment layers has been reduced to 3.536 V, and simultaneously, the decaying time is also shortened more than 18%. Notably, the vertical alignment of LCs was also stabilized under bending thanks to the use of undulating hybrid alignment layers. The fabricated flexible LC cell using 0.5% VO₂ nanoparticle doped h-PI alignment layers yielded good flexibility at a bending radius of 1500 mm without aggravated light leakages and deduced electro-optical performance, and the VO₂ agglomerates hindering the slide of LCs by providing adequate obstructions are believed as the main contributors in firmly stabilizing the vertical alignment of LCs during bending. Compared to micropatterned substrates, ultrathin VO₂ nanoparticle doped h-PI alignment layers employed in flexible LC cells demonstrating their priorities in easy investigation and displaying quality improvement are emerging, highly appreciated, and of great interest for the potential applications in flexible LCDs.