The Preparation And Study Of Polymer-Stabilized Cholesteric Liquid Crystals As Tunable Light-Reflector With Low Energy Consumption

Cholesteric liquid-crystals(CLCs)are one-dimensional photonic-crystals,which,due to their spontaneous self-assembly capability of a periodic helical structure,exhibit both circularly-polarized and selective reflection characteristics.As one of the most promising intelligent materials in the field of optoelectronics technology,it is favored by researchers.In particular,the reflection bandwidth of polymer-stabilized cholesteric liquid-crystals(PSCLCs),with negative dielectric-anisotropy,can be broadened by applying a directcurrent(DC)electric field.This class of materials is particularly interesting for its use in reflective display,information storage,laser radiation,smart dimming glass and other areas.In this paper,the properties of polymer-stabilized cholesteric liquid-crystals system with and without alignment layers under DC electric field have been studied.A lowvoltage tunable reflector based on polymer-stabilized cholesteric liquid-crystals system has been fabricated by removing alignment layers.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.The bandwidth broadening in polymer-stabilized cholesteric liquid-crystals system is ascribed to the polymer-network movement,when exposed to a DC electric field.However,due to the presence of ionic impurities in polymer-stabilized cholesteric liquid-crystals,the polarity of the electric field will inevitably lead to ion charge migration and accumulation.Therefore,dielectric spectroscopy is introduced to study the dielectric properties of polymer-stabilized cholesteric liquid crystal system under the action of electric field.This study shows that interfacial polarization(or electrode polarization),dipole-oriented polarization and DC conductance contribute to the complex dielectric constant of polymer-stabilized cholesteric liquid-crystals system.The electrode polarization leads to the formation of double electric layers in polymer-stabilized cholesteric liquid crystals system without alignment layers which have the same shield effect on the electric field as the alignment layers.It is of great significance to study the dielectric properties of polymer-stabilized cholesteric liquid-crystals system from the perspective of basic application and technological development.In addition,the transient-and steadycurrents across polymer-stabilized cholesteric liquid-crystals system under DC voltages can be used to study the motion and spatial distribution of ionic impurities,the motion of polymer networks,and the redistribution of voltage in the system.Our results indicate that the shielding effect of both the electric double layers and alignment layers is the main reason for voltage loss.This study is helpful to improve the fabrication of energy-saving devices and to explore new ways to improve the performance of polymer-stabilized cholesteric liquid-crystals.