Polymer-stabilized Liquid Crystal Films Research Articles

Study on the Effect of Monoacrylic Monomers on the Polymer Network Morphology and Electro-Optical Performance of Reverse-Mode Polymer Stabilized Liquid Crystal Devices

A polymer-stabilized liquid crystal (PSLC) device has been a promising candidate in several scenarios like smart vehicle windows and glass curtain walls in recent years due to its remarkable features like a fast switch from the initial transparent state to the scattering state with a rather low driving voltage, high transmittance at off-state, and broad viewing angle. The electro-optical characteristics of PSLC devices are determined by the synergistic attributions of liquid crystal (LC) molecules and the influence of the polymer network exerted on the movement of LC molecules. A systematic study of the influence of the polymer network on the movement of LC molecules is conducted, with the polymer network formed by methoxy/cyano/carboxyl monomers and diacrylate C6M. The polymer network morphology of PSLC film is greatly affected by the molecular structures and content of monoacrylic monomers. Additionally, the electro-optical performance and peel strength of PSLC films could be improved by modulating the molecular structures and morphology of polymer networks. PSLC devices containing carboxyl monomers show enhanced electro-optical performance and peel strength due to their directional filiform topology. This study might provide guidance for optimizing the performance of PSLC devices and establishing the relationship between the molecular structure, polymer network morphology, and electro-optical performance of reverse-mode dimming films.

Preparation of Highly Durable Reverse-Mode Polymer-Stabilized Liquid Crystal Films with Polymer Walls.

Reverse-mode polymer-stabilized liquid crystal (PSLC) films have wide applications in smart windows for cars as well as buildings and dimming glasses due to their low haze, low energy consumption, and better safety in case of emergency power off. However, PSLC films usually have poor stability of electro-optical properties due to their low polymer content (ca. 5 wt %), and it still remains a challenging task to improve the stability and processability by increasing the polymer content in PSLC as the driving voltage might dramatically increase. In this work, a reverse-mode PSLC film with polymer walls was prepared, which showed excellent stability of electro-optical properties even after 150 000 cycles. The film was prepared through polymerization with a photomask, in which the monomers concentrated on specific areas to form patterned polymer walls. In this way, the polymer content could be increased dramatically and the anchoring effect would not be too strong, thus avoiding a sharp increase in the driving voltage. As a result, the desired reverse-mode film with high stability, relatively low driving voltage, and high contrast ratio was obtained. The effects of monomer compositions, curing temperature, UV light intensity, and the pattern of the photomask on the microstructures, as well as electro-optical performances of the films were carefully studied. This work provides a new idea for the preparation of reverse-mode electrically switchable light-transmittance controllable films with excellent stability and good electro-optical performance, which would broaden their application in smart cars, building windows, and dimming glasses for light management and potential energy saving.

Reverse-mode PSLC multi-plane optical see-through display for AR applications.

In this paper we propose an optical see-through multi-plane display with reverse-mode polymer-stabilized liquid crystal (PSLC). Our design solves the problem of accommodation-vergence conflict with correct focus cues. In the reverse mode PSLC system, power consumption could be reduced to ~1/(N-1) of that in a normal mode system if N planes are displayed. The PSLC films fabricated in our experiment exhibit a low saturation voltage ~20 Vrms, a high transparent-state transmittance (92%), and a fast switching time within 2 ms and polarization insensitivity. A proof-of-concept two-plane color display prototype and a four-plane monocolor display prototype were implemented.

Preparation and thermo-optical characteristics of a smart polymer-stabilized liquid crystal thin film based on smectic A–chiral nematic phase transition

A smart polymer stabilized liquid crystal (PSLC) thin film with temperature-controllable light transmittance was prepared based on a smectic-A (SmA)–chiral nematic (N*) phase transition, and then the effect of the composition and the preparation condition of the PSLC film on its thermo-optical (T-O) characteristics has been investigated in detail. Within the temperature range of the SmA phase, the PSLC shows a strong opaque state due to the focal conic alignment of liquid crystal (LC) molecules, while the film exhibits a transparent state result from the parallel alignment of N* phase LC molecules at a higher temperature. Importantly, the PSLC films with different temperature of phase transition and contrast ratio can be prepared by changing the composition of photo-polymerizable monomer/LC/chiral dopant. According to the competition between the polymerization of the curable monomers and the diffusion of LC molecules, the ultraviolet (UV) curing surrounding temperature and the intensity of UV irradiation play a critical role in tuning the size of the polymer network meshes, which in turn influence the contrast ratio and the switching speed of the film. Our observations are expected to pave the way for preparing smart PSLC thin films for applications in areas of smart windows, thermo-detectors and other information recording devices.

All-optical and polarization-independent spatial filter based on a vertically-aligned polymer-stabilized liquid crystal film with a photoconductive layer

An all-optical and polarization-independent spatial filter was developed in a vertically-aligned (VA) polymer-stabilized liquid crystal (PSLC) film with a photoconductive (PC) layer. This spatial filter is based on the effect of light on the conductivity of PC layer: high (low)-intensity light makes the conductivity of the PC layer high (low), resulting in a low (high) threshold voltage of the PC-coated VA PSLC cell. Experimental results indicate that this spatial filter is a high-pass filter with low optical-power consumption (about 1.11 mW/cm(2)) in an optical Fourier transform system. The high-pass characteristic was confirmed by simulation. Accordingly, the all-optical and polarization-independent spatial filter can be used to enhance the edges of images.

Polymer stabilized liquid crystal films reflecting both right- and left-circularly polarized light

A single-layer polymer stabilized liquid crystal (PSLC) film reflecting both right- and left-circularly polarized light has been developed by a wash-out/refill method. The PSLC film was achieved by prefabricating the polymer network with a left-handed helical structure and then refilling a cholesteric liquid crystal with a right-handed helical structure into the network. The reflection intensity of the PSLC film is close to 100% when the pitch lengths of the two opposite helical structures are the same. It was demonstrated that the memory effect of the polymer network is an important mechanism for the resulting film properties.

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal (PSLC) film is a relatively novel electro-optical material, which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal. In this paper, the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation. The effects of liquid crystal concentration, curing time, monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated. The results show that the transmittance in the OFF state (T OFF) increased with the liquid crystal concentration, but the driving voltage decreased. T OFF was also influenced by the curing time. Furthermore, when polyimide was used as alignment layer, the films prepared from the bifunctional monomer shows a higher T OFF, while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks.