Influence Of Liquid Crystals Compositions On The Holographic Polymer Dispersed Liquid Crystals

Holographic polymer dispersed liquid crystals(HPDLCs)not only record both the phase and amplitude information of the coherent lasers,but also integrate the unique electro-optical properties of liquid crystals and excellent processability of the polymer.HPDLCs,compared with embossing singholographic technology,present many advantages such as low cost,high resolution,strong stereo sense,high photosensitivity,large image storage capacity,and great image storage stability.HPDLCs usually suffer from relatively low diffraction efficiency,high switching voltage and high light scattering which hinders their practical applications.In this regard,it remains a big challenge to form HPDLCs with concurrent features of low driving voltage,high diffraction efficiency,and low light scattering via a simple method.In this contribution,a novel approach that relies on simple LCs mixing is proposed to optimize the diffraction efficiency and driving voltage of HPDLCs.We synthesized LC 4-butyloxy-4’-cyanobiphenyl(4OCB),and mixed it with commercially available nematic LCs named P0616 A.These new LCs mixtures were then homogeneously mixed with monomers and a photoinitibitor composed of 3,3′-carbonylbis(7-diethylaminocoumarin)(KCD)and N-phenylglycine(NPG),followed by patterning using coherent lasers,generating well-structured HPDLCs.Introducing the LC 4OCB into the standard formulation is found to be able to tailor the polymerization kinetics and gelation behavior during the formation of HPDLCs,and to optimize the morphological and electro-optical properties of the resulting HPDLCs transmission gratings.By doping 5 wt% LC 4OCB into the HPDLCs,a high diffraction efficiency of 92.0 ± 2.8% is obtained;meanwhile,the threshold and saturated voltages significantly decrease by 80.8%(i.e.,from 12.0 ± 0.8 to 2.3 ± 0.9 V/μm)and 73.2%(i.e.,from 19.0 ± 0.6 to 5.1 ± 0.7 V/μm),respectively,in comparison with the pristine.The enhanced performance is believed to be ascribed to the large LCs droplets(70 ± 20 nm)and the lower surface anchoring strength(0.7 μN/m)of the polymer network on the LCs.In this dissertation,to solve the shortcomings of the HPDLCs gratings with high light scattering,ZnS nanoparticles(NPs)with a diameter of 5.5 ± 1.9 nm were synthesized via a simple “one-pot” procedure and surface-functionalized with a 2.5:1 molar ratio of 4’-(8-mercaptooctyloxy)biphenyl-4-carbonitrile(8OCBSH)ligands and hexanethiol ligands attached via the ZnS-S bond.These LCs functional ZnS NPs with a large refractive index(1.81)combine the advantages of the LC 8OCBSH and ZnS NPs.The homogeneously binary mixtures consisting of ZnS NPs and LCs P0616 A were prepared and further mixed with monomer and the photoinitibitor composed of KCD and NPG.Well-defined scaffolding structures of HPDLCs were finally formed by exposing the mixture to 460 nm coherent lasers.By loading 6 wt% ZnS NPs concentration,HPDLCs gratings with low light scattering loss of 4 ± 2%(dreasing by 66.7%)and high diffraction efficiency(93 ± 2.3%)were formed.Finally,we successfully reconstructed the 2D colored images from 3D real objects by a one-step holographic image storage technique.The reconstructed images were readily identifiable to the naked eye under daily-used light and show a great potentical in the field of high-end anti-counterfeiting.