Polymer Stabilized Liquid Crystal Smart Window with Flexible Substrates Based on Low-Temperature Treatment of Polyamide Acid Technology

Abstract

Polymer stabilized liquid crystal (PSLC) devices can be used as smart privacy windows that switch between transparent and opaque states. The polyimide alignment layer of a PSLC device is usually obtained by the treatment of polyamide acid (PAA) with temperatures over 200 °C. This hinders the fabrication of PSLC devices on flexible substrates, which melt at these high temperatures. In this work, the fabrication of a PSLC alignment layer using a lower temperature that is compatible with most flexible substrates, is demonstrated. It was found that the treatment of PAA at 150 °C could generate the same alignment for liquid crystals. Based on this, a PSLC device was successfully fabricated on a flexible polyethylene terephthalate (PET) substrate, demonstrating excellent electro-optic performances.

Electroconvection in Zwitterion‐Doped Nematic Liquid Crystals and Application as Smart Windows

“…The LC mixture is often used for the fabrication of LC‐based smart windows, due to its relatively large birefringence and dielectric anisotropy. [ 8,9 ] The LC mixture belongs to the (−, +) type, where the first − sign means negative dielectric anisotropy and the second + sign means positive conductivity anisotropy (∆σ = σ // – σ ⊥ ). After mixing with 0.1 wt% zwitterion Reichardt's dye, the mixture shows a clearing temperature around 93 °C (Figure S1, Supporting Information).…”

“…Liquid crystal (LC) is an interesting class of materials with anisotropic optical and dielectric properties, which is widely used in liquid crystal displays (LCDs), smart windows, adaptive coatings, and many other electro‐optic devices. [ 1–9 ] One field‐induced effect in LCs is called electroconvection (EC), or electro‐hydrodynamic instability (EHDI), which is a dissipative process associated with the occurrence of a mechanical flow and relatively large electric current. [ 10 ] It is well known as one of the first LCD technologies, and has been extensively studied as a model system for the formation of regular nonequilibrium structures, such as rolls, chevrons, squares, fingerprint, bimodal varicose, and cellular or wavy patterns.…”

Reverse Mode Polymer Dispersed Liquid Crystal-based Smart Windows: A Progress Report

“…This limits the fabrication of PSLC on the flexible films, as they usually melt or degrade at such high temperatures. Zhang et al reported that low-temperature (incomplete imidization) treatment of PAA neither negatively affects the homeotropic alignment of the LCs, nor impacts the formation of a polymer network on PSLC [34] (Figure 4a). The results presented herein lay a solid foundation for the development of flexible PSLC films.…”

“…The preliminary results indicate improved adhesion strength at the interface [35]. We believe that once successfully developed, flexible PSLC films shall accelerate the advancement of the field related to smart windows.. [34]. Cross-sectional SEM images of the polymer networks (for PSLC) with alignment layers fabricated using b) polyimide and c) bifunctional silanes [35].…”

“…Figure 4 a) Electro-optical performance and images of PSLC fabricated on the flexible substrate in the OFF/ON states[34]. Cross-sectional SEM images of the polymer networks (for PSLC) with alignment layers fabricated using b) polyimide and c) bifunctional silanes[35].…”