Investigation On The Performance Of Patterned Cholesteric Liquid Crystal Fingerprint Textures With Optically Controllable Capabilities

Cholesteric liquid crystals(CLCs)with self-assembled helical superstructures have been widely utilized in the fields including thermography for reflective displays,temperature sensing,biosensing,tunable color filters,polarizers,switchable smart windows for controlling interior temperature and brightness,fast and high contrast flexoelectro-optic devices and etc.due to their responsive properties to external stimuli such as electric field,magnetic field,light irradiation,temperature,mechanical force,and surface effect.The axis of the helical superstructure lies in the plane of the substrate with the help of electric field and CLCs commonly exhibit fingerprint texture under a polarized optical microscope(POM).The periodic modulation of refractive index along the plane of the substrate of CLCs qualifies them as the excellent Raman-Nath diffraction gratings,which makes CLC fingerprint texture has been employed in beam steering,brightness enhancement,dynamic lithography masks,smart coatings,particle manipulation,liquid crystal(LC)lasers and optical anti-counterfeiting and etc..With the development of interdisciplinary cooperation,researchers working on LCs have been attracted to the dynamic manipulation of the helical superstructures of CLCs in two-dimensional or three-dimensional space.The complex and practial multidimensional photonic materials are promising to be created with the studies of a complex self-assembled system based on the CLC fingerprint texture patterning.Here,we present two different mechanisms of CLC fingerprint texture patterning by optical tuning with the help of photoconductive material as one substrate of the CLC cell or azobenzene dye as the alignment layer.The main investigation could be divided into two parts as follows:1.Photoconductive CLC samples were prepared by using BSO crystal as one substrate of CLC cell.Then Ultraviolet(UV)light was used to reduce the impedance of BSO substrate to control the voltage on the CLC layer,thereby obtaining the desired textures of CLCs by both electric field and light irradiation with the aid of BSO sunstrate acts as virtual electrode.After studying the optical performance of the photoconductive CLC samples,combined with the DMD system,the complex subregional arrangement of the CLC helical superstructures was achieved,that is,the dynamically responsive patterning of CLC helical superstructures by optical tuning.2.With the assistance of a driven electric field,the uniform CLC fingerprint texture was formed based on the azobenzene dye SD1 as the alignment layer.Simultaneously,the UV light with high intensity was applied to get a periodic grating imprint texture on the alignment layer,which owned the same period and direction of the fingerprint texture presented during the irradiation.By studying the generation and characteristics of the grating imprint structure,combined with multiple exposures by mask or patterned exposures of the DMD system,two types of optically tuned grating imprint patterning were formed based on CLC fingerprint texture.