Electro-optical and dielectric properties of polymer-stabilized blue phase liquid crystal impregnated with a fluorine-containing compound

A Review of Developments in Polymer Stabilized Liquid Crystals

Polymer-stabilized liquid crystals (PSLCs) are multi-functional materials consisting of polymer networks in a continuous phase of liquid crystals (LCs), of which polymer networks provide anchoring energy to align the LCs. A number of improvements are detailed, including polymer-stabilized nematic liquid crystals (PSNLCs), polymer-stabilized cholesteric liquid crystals (PSCLCs), polymer-stabilized blue phase liquid crystals (PSBPLCs), polymer-stabilized smectic liquid crystals (PSSLCs), polymer-stabilized ferroelectric liquid crystals (PSFLCs), and polymer-stabilized antiferroelectric liquid crystals (PSAFLCs) in this review. Polymer stabilization has achieved multiple functionalities for LCs; in smart windows, a sufficiently strong electric field allows the LCs to reorient and enables switching from a scattering (transparent) state to a transparent (scattering) state. For broadband reflectors, the reflection bandwidth of LCs is manually tuned by electric fields, light, magnetic fields, or temperature. PSBPLCs open a new way for next-generation displays, spatial light modulators, sensors, lasers, lenses, and photonics applications. Polymer networks in PSFLCs or PSAFLCs enhance their grayscale memories utilized in flexible displays and energy-saving smart cards. At the end, the remaining challenges and research opportunities of PSLCs are discussed.

Liquid crystal-photopolymer composite films for label-free single-substrate protein quantitation and immunoassay

Conventional liquid crystal (LC)-based biosensing at the LC-glass interface requires the assembly of an LC cell formed by two glass substrates with an LC film sandwiched in between. As most biochemical and clinical assays are performed on a single solid substrate, the feasibility of a single-substrate biodetection platform based on a thin film of LC-photopolymer composite was explored in this study. The LC mixture, consisting of nematic LC, E7 or AY40-006, doped with a small amount (≤ 5 wt%) of a photocurable prepolymer was spin-coated on a glass substrate modified with dimethyloctadecyl[3-trimethoxysilyl)propyl] ammonium chloride (DMOAP), a vertical alignment reagent, followed by irradiation with ultraviolet (UV) light. During the photopolymerization process, the accumulated and polymerized NOA65 at the LC-glass interface weakened the anchoring strength of DMOAP, resulting in a decrease in the pretilt angle of LC and allowing the LC molecules to be more easily disturbed in the presence of biomolecules, compared with vertically aligned LC in the absence of polymerized NOA65. Incorporating NOA65 in the LC film therefore provides a means for signal amplification. When an LC-photopolymer composite film consisting of AY40-006 and 4-wt% NOA65 was exposed to UV at 15 mW/cm² for 30 s and utilized as the biosensing mesogen, the limits of detection were 1.6 × 10^-12 g/ml for the direct detection of bovine serum albumin (BSA) and 2.1 × 10^-8 g/ml for the immunoassay of the cancer biomarker CA125, significantly lower than those detected with AY40-006 alone or AY40-006/NOA65 mixture without UV irradiation. The results from this study offer a compelling implication on the biomedical application of LC-photopolymer composites in label-free and single-substrate biodetection.