# Improvement of Electro-Optical Properties of PSLC Devices by Silver Nanowire Doping
## 1 Introduction  
Smart windows [1; 2] that can modulate light are a type of intelligent building material and can save energy in buildings. At present, most commercially available smart windows are controlled by electric field. Materials with such function are mainly liquid crystal (LC) [3; 4; 5] and electrochromic oxide. For LC based smart windows, the orientation of LC molecule will change when an electronic field is applied. The incident light will be modulated by the LC molecules, and be reflected, scattered and so on. Electrochromic materials show a change of color as induced either by an electron transfer (redox) process or by a sufficiently high electrochemical potential [6]. Compared with electrochromic smart glass, LC based smart glass has many advantages, such as low cost, good stability, easy regulation and fabrication of large size preparation. As a result, LC based smart windows are expected to occupy the mainstream of smart glass market [7]. Privacy windows that can switch between scattering state and transparent state are one of the most popular types of LC-based smart glass. There are two kinds of privacy windows: polymer dispersedliquid crystal (PDLC) based and polymer stabilized liquid crystal (PSLC) based [8; 9; 10]. PDLC is a composite material with submicron LC droplets embedded in a polymer matrix. Without an electric field, the LC molecules in the PDLC device are randomly orientated, scattering the incident light and the device is opaque. When an electric field is applied, the LC molecules are reoriented into the same direction and the device becomes transparent, with the transmittance approaching 90% with a sufficiently high electric field [11]. On the contrary, PSLC incorporates only small amount of polymer into LC material to stabilize the orientation of LC molecules. Without electric field, the LC molecules are orientated in the same direction as alignment layer and the polymer, and the device is transparent. With an applied electric field, the LC molecules are reoriented to the perpendicular direction. Since the polymer network will disturb and impede the rotation of LC molecules, a multi-domain structure will form and the incident light will be scattered, causing the device to become opaque [12]. In application, PSLC devices, which are transparent without electric field, are more economical and convenient than PDLC devices. Furthermore, PSLC devices have lower threshold voltage, shorter response time, higher contrast and wide viewing angle [13], making them also widely used as displays, spatial light modulators, hologram-formed light modulators [14], temperature sensors [15], flexible displays [16], and other devices besides smart windows. Although PSLC devices have been widely used, the critical electro-optical performance of the devices still needs to be optimized, including threshold voltage, response time and other optical parameters. In recent years, nanoscale materials have been widely used to improve the electro-optical response properties of LCs [17; 18; 19]. It has been found that the dispersed nanomaterial can change the properties of the host LC, such as the electrical, optical and magnetic properties [20]. At the same time, the nanomaterial can trap ions in LC material, decreasing the ion concentration and conductivity of LC, which would improve the electro-optical property of the LC host [21]. [PERSON] et al. doped titania nanoparticles of different sizes in nematic LCs. They observed that smaller size nanoparticles can lower the threshold voltage of the device [22]. Others have doped metal oxide nanoparticles (MgO, SiO\({}_{2}\) and Y\({}_{2}\)O\({}_{3}\)) [23; 24] in a nematic LC matrix. The order parameters of the LC-NP composite are reduced, which leads to a reduction in the threshold voltage required to redirect the LC director along the applied electric field. The doping of noble metal nanoparticles in PDLC device will cause surface plasmon excitation at the nanoparticle-polymer interface [25] and influence the electro-optical properties of PDLC. [PERSON] et al.