| Cholesteric liquid crystals(CLCs)have the characteristics of dynamic changes in the pitch and the wavelength of the reflected light under a variety of external stimuli(such as light,electricity,heat,etc.).This paper mainly studied the dynamic modulation of multi-tone Bragg reflected light of the CLCs and the polymer-stabilized cholesteric liquid crystals(PSCLCs)under the change of the ambient temperature.The main research contents include:(1)Based on the chiral molecular S811 doped liquid crystal E7,we designed and prepared a temperature-responsive CLCs system,and systematically studied the dynamic change laws of the colors and characteristic peaks of the reflected light in the visible band by the heating and cooling of a hot stage.The results show that CLCs have reversible temperature-responsive characteristics.What’s more,with the increase of temperature,the CLCs system unwound and the color of the reflected light was observed by polarizing microscope(POM),which gradually changed from red to orange-yellow,yellow-green,and finally blue-green.The characteristic peak of the reflected light was also significantly blue-shifted under the optical fiber spectrometer,resulting in the adjustable band gap width of 240 nm.The temperature-responsive CLCs not only have excellent reversible temperature response performance,but also have excellent photo-electrical characteristics.The threshold voltage was found to be 38.109 V by ALCT liquid crystal parameter test instrument.(2)Based on the RM257 with different concentrations and a small amount of photoinitiator doped CLCs,we designed and prepared temperature-responsive PSCLCs systems,and systematically studied the dynamic changes of colors and characteristic peaks of the reflected light in the visible band.The results show that the RM257 forms a network structure between CLCs molecules through polymerization and the network becomes dense with the increase of their doping concentration,but PSCLCs still have reversible temperatureresponsive characteristics.With the increase of the temperature,the PSCLCs system unwound,so the color of the reflected light was observed by the POM to gradually change from red to orange-yellow,yellow-green,and finally blue-green in a narrow temperature range(compared with CLCs),which is more sensitive temperature-responsive.However,the reflective colors of PSCLCs with a denser network structure became no longer easily observable;The characteristic peak of the reflected light of the PSCLCs system was found a obvious blue-shift under the optical fiber spectrometer,and the band gap of the reflected light was adjustable to 240 nm.We believe that the local limiting effect and thermal conductivity effect of the network structure formed by the polymerization of liquid crystal monomer are the main reasons for improving the temperature sensitivity of PSCLCs.At the same time,we found that compared with CLCs,the intensity of the reflected light of PSCLCs decreased,and decreased more significantly with the increase of RM257 doping concentration.This is mainly because the content of the CLCs of the incident light that is effectively reflected in PSCLCs is reduced with the increase of the doping concentration of the RM257,and CLCs have a completely different refractive index with the network structure,which result in the reflection effects of PSCLCs not being comparable with CLCs systems.The temperature-responsive PSCLCs not only have excellent reversible temperature-responsive performance,but also have excellent photo-electrical characteristics,so the threshold voltage of PSCLCs prepared by 1% RM257 doped in CLCs was only 34.696 V by ALCT liquid crystal parameter test instrument.(3)In order to improve the reflection intensity of PSCLCs,we designed and prepared temperature-responsive Ag-PSCLCs systems by doping Ag nanoparticles,and systematically studied the changes of the reflection intensity in the visible band.The results show that due to the high reflectivity and the surface resonance effect of Ag nanoparticles,their doping in PSCLCs can overcome the mismatch between the refractive index of polymers and liquid crystals to some extent,so that the reflectivity of Ag-PSCLCs system is improved.Compared with PSCLCs,the intensity of the reflected light of Ag-PSCLCs increased significantly with the increase of the doping concentration of Ag nanoparticles.Among them,the intensity of the reflected light of PSCLCs was increased by more than 36% by doping with 0.1% Ag nanoparticles,but the adjustable width of the band gap of the reflected light was still higher than 240 nm.Ag-PSCLCs still have excellent photo-electrical characteristics,and the threshold voltage of PSCLCs doped with 0.1% Ag nanoparticles(RM257 content is 1%)was only43.046 V by ALCT liquid crystal parameter test instrument.In this paper,the systems of Ag nanoparticles-doped PSCLCs were prepared,and the bandgap characteristics of the reflected light during heating and cooling were systematically studied.The results show that Ag-PSCLCs not only have dynamically adjustable temperatureresponsive characteristics similar to PSCLCs,but also have adjustable reflected light intensity based on changing the doping concentration of Ag nanoparticles.It can be seen that AgPSCLCs have significant advantages in the application fields of colorimetric temperature sensors and intelligent anti-counterfeiting labels. |
