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The reflection bandwidth of polymer-stabilised cholesteric liquid-crystals (PSCLCs), with negative dielectric-anisotropy, can be broadened by applying a direct-current (DC) electric field. This class of materials is particularly interesting for its use in displays, optical storages, tunable lasers, or energy-conserving windows. The transient- and steady – currents across PSCLCs under DC voltages can be used to study the spatial distribution of charged bodies and the motion of the polymer network. Our results indicate that the shielding effect of both the electric double layers (EDLs) and alignment layers is the main reason for voltage loss. The electric-field threshold for reflection-band broadening decreases to 0.05 V/μm after the alignment layers were removed, and the power consumption also drops by nearly tenfold. This study helps to improve the fabrication of energy-saving devices and to explore new ways to improve PSCLCs. [ABSTRACT FROM AUTHOR]

By simulating the dynamic response processes of reverse-mode polymer-stabilised cholesteric texture (PSCT) via double exponential rise/decay model, the deformation of polymer networks were quantitatively characterised. The polymer network deformation is shown to be controlled by regulating monomer concentration and the applied electric field. Increased monomer concentration facilitates the production of polymer fibrils of a higher polymer molecular weight while suppressing distortion of the polymer network. Decreased polymer network deformation assists in the decrease of the undesired hysteresis phenomenon while also demonstrating a shorter field-off response time of PSCT; however, the trade-off is increased operation voltage and decreased contrast ratio. The observed results provide useful guidelines for future PSCT material and device optimisations. [ABSTRACT FROM AUTHOR]

We investigate the process and the resulting properties of the curing electric-field-induced segregation of reactive monomers (containing polar groups) in a host liquid crystal. The obtained dielectric spectrum of these cholesteric liquid crystals (CLCs) reveals polarisation at low frequencies. This is a strong indication that charge carriers accumulate at the interface between the sample and the electrodes in these compounds and consistent with Maxwell–Wagner–Sillars (MWS) polarisation. A polymer film forms on the substrate with its thickness determined by the MWS polarisation strength. The SEM images show that the polymer network becomes less dense when MWS polarisation increases. The results are a higher operating voltage and faster response time. [ABSTRACT FROM PUBLISHER]

The effects of cell gap on the electro-optical properties of normal-mode polymer-stabilised cholesteric texture (PSCT) have been investigated. In this study, the size of the domain and electro-optical properties of PSCT are analysed as a function of the thickness of the cells. Increasing cell gap helps to improve the contrast ratio, but the threshold voltage would increase simultaneously. The scanning electron microscopy indicates that the polymer networks are tightened with increasing cell gap. A denser polymer network leads to smaller domain size, higher effective electric field and decreased field-off response time. [ABSTRACT FROM AUTHOR]

The effect of curing frequency on the morphology of polymer networks and the electro-optical property of normal-mode polymer-stabilized cholesteric textures (PSCTs) has been investigated. The scanning electron microscopy indicates that the shape of polymer networks transforms from honeycomb-like to fiber-like due to the increased solubility of the monomer at higher curing frequencies. The PSCTs cured at lower frequencies with sufficiently large network voids show a two-stage reorientation process that correlates with two kinds of cholesteric liquid crystal (LC) under different environments. The threshold voltage decreases as the curing frequency increases from 1 Hz to 10,000 Hz, while the field-off response time increases. [ABSTRACT FROM AUTHOR]