Enhanced reflection band broadening in polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy

Recent Advances in Electro-Optic Response of Polymer-Stabilized Cholesteric Liquid Crystals

Cholesteric liquid crystals (CLC) are molecules that can self-assemble into helicoidal superstructures exhibiting circularly polarized reflection. The facile self-assembly and resulting optical properties makes CLCs a promising technology for an array of industrial applications, including reflective displays, tunable mirror-less lasers, optical storage, tunable color filters, and smart windows. The helicoidal structure of CLC can be stabilized via in situ photopolymerization of liquid crystal monomers in a CLC mixture, resulting in polymer-stabilized CLCs (PSCLCs). PSCLCs exhibit a dynamic optical response that can be induced by external stimuli, including electric fields, heat, and light. In this review, we discuss the electro-optic response and potential mechanism of PSCLCs reported over the past decade. Multiple electro-optic responses in PSCLCs with negative or positive dielectric anisotropy have been identified, including bandwidth broadening, red and blue tuning, and switching the reflection notch when an electric field is applied. The reconfigurable optical response of PSCLCs with positive dielectric anisotropy is also discussed. That is, red tuning (or broadening) by applying a DC field and switching by applying an AC field were both observed for the first time in a PSCLC sample. Finally, we discuss the potential mechanism for the dynamic response in PSCLCs.

Broadband reflection in polymer-stabilized cholesteric liquid crystals via spin-coating MoO2 nanoparticles

The SEM image of the polymer network of samples e1–e5: (e1) 4.8% C6M; (e2) 6.8% C6M; (e3) 8.8% C6M; (e4) 10.8% C6M; (e5) 12.8% C6M; and (e4′) cross-sectional image of e4.

Biomimetic Solid-Liquid Transition Structural Dye-Doped Liquid Crystal/Phase-Change-Material Microcapsules Designed for Wearable Bistable Electrochromic Fabric

A novel polymer microcapsule-filled dye-doped liquid crystal (DDLC) and phase-change material (PCM) system inspired by biological materials was first proposed, which was further encapsulated into a calcium alginate substrate by wet spinning for making an electrochromic fiber with both bistable electric-optical capability and knitting characteristics. Results show that the optical appearance of the optimized microcapsules and fiber can be reversibly changed between colored and colorless states according to the electric field by switching the DDLCs between isotropic (I) and anisotropic (A) states. Moreover, both I and A states can remain stable for more than 1 week after removing the electric field, due to the synergy of the greatly increased spatial hindrance of the PCM with core loading of 22.58% and the confinement effect from the polymer microcapsule shell material. Aside from the long-term optical stability, the high content of the densely packed DDLCs also endows the electrochromic fiber with a satisfactory driving voltage of 9.7 V, which is below the human safe voltage, showing great potential in a wide range of applications, such as flexible displays, energy-saving smart windows, and wearable advanced textiles.

Optical properties of electrically controlled arc-electrode liquid-crystal microlens array for wavefront measurement and adjustment

An electrically controlled arc-electrode liquid-crystal microlens array (AE-LCMLA), with tuning and swing focus, is proposed, which can be utilized to replace the traditional mechanically controlled microlenses and also cooperate with photosensitive arrays to solve the problems of measuring and further adjusting a strong distortion wavefront. The top patterned electrode of a single LC microlens is composed of three arc-electrodes distributed symmetrically around a central microhole for constructing the key controlling structures of the LC cavity in the AE-LCMLA. All the arc-electrodes are individually controlled, and then the focal spot of each microlens can be moved freely in a three-dimensional fashion including along the optical axial direction and over the focal plane by simply adjusting the driving signal voltage applied over each arc-electrode, independently. The featured performances of the AE-LCMLA in a wavelength range of ∼501-561  nm are the driving signal voltage being relatively low (less than ∼11  V_rms), the focal length tuning range being from ∼2.54  mm to ∼3.50  mm, the maximum focus swing distance being ∼52.92  μm, and the focus swing ratio K being ∼20‰.