Study On Electro-Optical Characteristics And Laser Protection Properties Of Composites Based On Azo-dichroic Dye-doped Liquid Crystals

With the development and widespread application of laser technology, the protection of human eyes and sensors against intended or unintended damage by laser radiation is a hot research topic. The major drawbacks of the conventional laser protective materials are as the following:(1) the protection laser wave radiation is limited to a specific wavelength only; (2) these devices cannot be intelligent controlled by electric field in the states of protection and un-protection. It is found that GH LC composites are highly potential for laser protection, and would undoubtedly guard against the shortcomings of conventional materials. In this thesis, a novel type of smart laser protection materials with the protection state controlled by electric field were prepared by doping three commercially available azo-dichroic dyes into LC hosts based on the principle of GH interaction. The main research contents are listed as follows:(1) The LC composites based on three commercially available azo-dichroic dyes with different absorption spectrum (400～700 nm) doped the nematic liquid crystals (DDNLC) were successfully prepared, and the effects of the dichroic dyes concentration on the electro-optical characteristics and laser protection performances were investigated. The experimental results showed that the films had a lower and higher transmittance of incident light across the whole visible region without and with an electric field applied, respectively. Therefore, the obtained GH-films can absorb the laser of wide-band visible light ranging from 400 to 700 nm without using of polarizer due to the different light absorption centers of the three dyes. Most importantly, different from other traditional laser protective materials, the transmittance of the GH-films can be modulated by applying electric field. Moreover, the composites have characteristics of no colour distortion low driving voltage, fast response time and good stability under an electric field, etc.(2) The laser protection composites with Bragg reflection and wideband light absorption characteristics based on above-mentioned azo-dichroic dye-doped cholesteric liquid crystals(DDCLC) were successfully prepared by the use of the Bragg selectively reflection characteristics of the cholesteric liquid crystals. Experimental results showed that the pitch of the ChLC plays an important role in determining the electro-optical characteristics and laser protection properties of DDCLC films. Both Vth and Vsat continuously increased with the decrease of pitch. Moreover, the D and CR of the films were to further improve. The films’ Vth and Fsat were higher compared with the system of DDNLC. It was mainly due to the shorter the pitch of ChLC, the greater the helical twisting force, therefore the Vth and Vsat of DDCLC films are inversely proportional to the pitch of the ChLC.(3) The composite films were prepared by doping three commercially available azo-dichroic dyes into polymer dispersed liquid crystals (DDPDLC) based on combining the scattering characteristics of PDLC with absorption of dyes. It was found that the LC domain size was gradually increased with increasing of the azo-dyes’ concentration. Due to the absorption ultraviolet light of the azo-dichroic dyes, the rate of polymerization was slow down with the decreased UV light intensity in the process of monomers polymerization, result in the LC domain size increased in the PDLC films.