Preparation And Spectral Properties Of Liquid Crystal/Metal Nanostructure Composites

The optical properties of metal nanostructures based on the surface plasmon resonance(SPR)effect are attracting more and more attentions in the fields of fluorescence enhancement,biological detection,dynamic color display and anti-counterfeiting identification.Meanwhile,due to the characteristics of the orientation of the liquid crystals(LCs),the combination of LCs and metal nanostructure materials brings new vitality to the plasmonic metal nanostructures.Regulating the SPR spectra of the metal nanostructures effect by employing the LCs has become a new research hotspot,wherein the orientation of the LCs could be changed upon the external stimuli.In this study,two different LC-metal nanostructure composite systems were designed and the spectral properties of these two systems were investigated.First,a gold nanorod doped nematic LC elastomer(LCE)composite film was prepared,and the transmitted light spectrum was measured when the angles between the LC orientation and the polarized light are 0°and 90°,respectively.The results show that the longitudinal plasmon resonance peaks of the gold nanorods are at high intensity when the angle between the LC orientation and the polarized light is 0°,and the longitudinal plasma resonance peaks of the gold nanorods at low intensity when the LC orientation and the polarized light angle are 90°.The film color is blue-green when the angle is 0° observed under the polarized light microscope,while it is pink when the angle is 90°.Based on the above studies,the dichroic pattern of the LCE-based composite film was fabricated by employing two-time exposure method.Second,an aluminum(Al)-dielectric-Al trilayer composite structure was prepared,and the SPR spectra of the nanostructure with nematic LC(N-LC)under external electric field was investigated.In order to rationally design the composite structure,we used the numerical simulation software COMSOL based on finite element method(FEM)to obtain the specific parameters of the composite system.The results show that the SPR spectra was effectively tuned due to the changes the effective refractive index of the plasma nanostructure surface when the LC molecules transformed from planar orientation to vertical orientation triggered an external electric field.To summarize,two novel LC-metal nanostructure composite materials were investigated in this study,which paves a new way for the development of the metal nanomaterials and LC materials.These composite materials also have potential applications in the fields such as novel LC displays and optical functional films.