Study Of Self-Assemblies Of Silver Nanowires In Liquid Crystals And Their Electric-Optic Properties

Functional nanomaterials can self-assemble into ordered superstructures,and the newly structured materials will exhibit their unique properties in physics,chemistry,biology and medicine.With the continuous advancement of nanomaterial orientation technology,various functional small-sized nanomaterials have been successfully self-assembled,showing significant application value in multiple fields,such as optical imaging,biosensing,electronic skin,and optoelectronic detection.Currently,the aligned nanomaterials are relatively small in size,and it is difficult to achieve the multi-domain orientation of nanomaterials in the micro-region.Therefore,there is an urgent need for a new orientation method to realize the multi-domain self-assembly of large-size nanomaterials in the micro-region.With the development of photo-alignment technology,researchers have begun to focus on using photo-alignment technology to align nanomaterials.Silver nanowires(AgNWs)have been attracting the research interest of researchers as a material with high electrical conductivity and excellent surface plasmon resonance.Using photo-alignment technology,AgNWs were successfully self-assembled in liquid crystal(LC),and two multi-domain orientations of planar alignment and twisted nematic models were achieved in the micro-region,which will facilitate the preparation of high-performance new information devices based on AgNWs and provide certain value for aligning other large-sized nanomaterials.In this dissertation,the dispersion,orientation,reorientation,electric-optic(E-O)properties and flexible display of AgNWs in LCs and LC polymers(LCPs)were investigated based on the photo-alignment technique,and the results obtained are as follows:(1)AgNWs with large aspect ratio were prepared.AgNWs with a length of about 5.8 μm,a diameter of about 86.5 nm,and an aspect ratio of about 67 were prepared by a polyol reduction method.The AgNWs were wrapped with a layer of compound with a thickness of about 2.3 nm,which avoided the agglomeration among the AgNWs as well as provided the aligning force between the AgNWs and LCs.(2)AgNWs were self-assembled in LCs.The AgNWs were uniformly dispersed in the LC E7 and injected into an LC cell.Optical microscopy observation revealed that the long axis of the AgNWs was aligned along the LC director n in the cell,which was independent of the flow of the LC.The two-dimensional order parameter of the AgNWs was calculated to be about 0.9,indicating good orientation effects of the AgNWs in the LC.The planar alignment and twisted nematic multi-domain orientation of AgNWs in the micro-region were successfully achieved using a photomask and spatial light modulator.Because the photo-alignment layer is sensitive to the polarization direction of polarized blue light,dynamic changes of AgNWs in LCs were achieved by changing the direction of polarized light.Combined with the electric field,the orientation of AgNWs in LCs can be dynamically tuned in three dimensions.Since the size of AgNW is much larger than the LC molecule,the AgNWs will affect the orientation of nearby LC molecules,causing a weak scattering effect.(3)The effects of different concentrations of AgNWs on the E-O properties of LC devices were investigated.The AgNWs dispersed in LCs will affect the rotation of nearby LC molecules under the electric field due to their large length and diameter.The LC devices doped with higher concentration of AgNWs tend to require longer response time to complete the changes of LC molecules under the applied electric field and removed electric field.Also,the doping of AgNWs will increase the dielectric anisotropy and decrease the elastic constant of the mixture,which decreases the threshold voltage of the LC device.Due to the high electrical conductivity of AgNWs,the orientation of AgNWs under voltage will facilitate the transport of electrons in the device and improve the conductivity of the device.(4)AgNW/LCP film can be used for flexible display.To prevent the sinking and reaggregation of AgNWs in LCs,we use LCP to photo-polymerize the aligned silver nano wires.Similar to LC,the long axis of the AgNWs in the LCP is also aligned along the LC director n,with the order parameter of about 0.9.The AgNWs achieve planar alignment and twisted nematic in the micro-region with the photomask.Since the photo-alignment layer is soluble in deionized water,a detached AgNW/LCP film is obtained through immersion,and transferred to a flexible and transparent substrate,achieving flexibility and wearable display.Furthermore,the aligned silver nanowires enhance the tensile performance of the LCP film,which will be beneficial for the practical application of the LCP film.