A novel optical diffuser based on polymer micro-balls-filled nematic liquid crystal composite film

A bistable cholesteric liquid crystal film stabilized by a liquid-crystalline epoxy/thiol compound-based polymer

Bistable cholesteric liquid crystals have promising application prospects in various fields, such as smart windows and displays. However, the long-term stability of two individual states is not easy to achieve, hindering their practical use. In this research, the bistable feature was enhanced by constructing a microsphere-type polymer with a liquid-crystalline epoxy/thiol monomer in negative dielectric anisotropic cholesteric liquid crystals. Spectroscopic and optical examinations revealed that either the transparent planar state or the opaque focal conic state can be maintained without the aid of an external field. Moreover, they can be switched to each other by applying a high- or low-frequency electric field. Further, factors such as the chemical structure of thiol compounds, curing temperature and curing time were investigated to explore their influences on the micro morphology of the polymer and thereby the electro-optical properties. In addition, the frequency-dependent driving scheme was analysed. Finally, bistable switching was demonstrated using an optimized sample. This energy-efficient bistable film shines light on future applications in smart windows, photonic paper and other electro-optical devices.

A comprehensive review of optical diffusers: progress and prospects

Optical diffusers made of polymer composite materials are vital for many photonic and optoelectronic applictions such as backlight unit (BLU) in liquid crystal displays (LCDs), light extraction unit of organic light emitting diodes (OLEDs), and solar cells. We have described the types of optical diffusers, the theory and measurement of light scattering, some common approaches for fabricating optical diffusers, the potential applications and recent developments of optical diffusers containing optical physical unclonable functions (PUFs), optical random number generators, passive stretchable radiative coolers, diffuser -based deep neural networks, lensless cameras or imaging systems, and three dimensinonal (3D) displays including two dimensional (2D)/3D switchable displays, which provide effective ways for designing high-performance optical films in the applications of optical devices. To satisfy the requirements for applications in stretchable optoelectronics and optomechanics, tunable optical diffusers stimulated by electric field, heat, light, mechanical field, or ultrasound attract much attention. Polymer/liquid crystal (LC) composite films with tunable light transmittance, haze, and diffusing intensity have been firstly provided and set a great foundation for the next generation of flexible and switchable optical diffusers.

Thermoresponsive Reflective Scattering of Meso-Scale Phase Separation Structures of Uniaxially Orientation-Ordered Liquid Crystals and Reactive Mesogens

Polymer network liquid crystals (PNLCs) capable of thermoresponsive change in reflective scattering were fabricated using a self-organization technique called photopolymerization-induced phase separation. These PNLCs exhibit nonscattering states at temperatures τ below the nematic-to-isotropic (NI) phase transition temperature τ_NI but reflective scattering states at τ values above τ_NI. The magnitude of change of optical clarity is 80% and of solar transmittance is 20% in PNLCs with a thickness of 50 μm. The microscopic structures consist of wavelength- or meso-scale phase separation domains of liquid crystals (LCs) and polymerized reactive mesogens (RMs) in which cyanobiphenyl (CB) groups are thermoresponsively transformed between uniaxially orientation-co-ordered and disordered states. Such thermoresponsive structures were fabricated by employing the CB groups as mesogenic bodies, which were expected to mutually associate due to their physicochemical structures. Cross-linkers stabilized the meso-scale domains and made the PNLCs durable through repeated temperature changes. Polarizing optical microscopy (POM) and scanning electron microscopy showed meso-scale composites that reflectively scatter visible and near-infrared light. POM and Fourier-transform infrared spectroscopy at different temperatures suggest that the orientation order of the CB groups changes in the LC phase in response to temperature but remains ordered in the RM phase. Such a thermoresponsive change in the orientation order produces the switchability in meso-scale nonuniformity and consequently in reflective light scattering. The thermoresponsive PNLCs are not only effective as energy-saving smart windows but also advantageous at stages of manufacture, installation, and operation.