Research On Cholesteric Materials With High Contrast,Low Drive Voltage And Black-on White Display Mode

With the rapid development of electronic information science,The text information of many printed products is transmitted in the form of electronic documents.As a result,People have been receiving radiation damage from electronic displays for a long time.Therefore,a new type of information display vector is urgently needed to replace the old paper display and the traditional electronic display.Cholesteric bistable electronic display was born.Cholesteric bistable display utilizes its selective reflection and bistability,which makes the device have the advantages of low power consumption,no backlight and zero field memory.However,the existing cholesteric bistable display devices have some defects,such as poor background color,poor contrast,and complicated black-on-white process.In order to broaden the application field of cholesteric bistable liquid crystal,In this thesis,the influence of device design and material characteristics on the performance of cholesteric bistable liquid crystal display devices are studied.The details are as follows:(1)By setting the reflection wavelength of the plane state(P state)to the non-visible band and coating the device bottom with black ink,the so-called "black character" can be achieved;Focal cone state(FC state)is a semi-transparent and semi-reflective device due to its unique arrangement.By adjusting the collocation of liquid crystal materials,the scattering of focal cone state can be enhanced,and the so-called "white background" can be achieved.The experimental results show that P state can also achieve "black character" and FC state can also achieve "white background",which solves the background color problem of traditional cholesteric bistable liquid crystal.(2)The effects of cell thickness and surface properties on the characteristics of cholesteric bistable liquid crystal display were studied.The experimental results show that the larger the cell thickness,the higher the refresh voltage,and the higher the reflective intensity of FC and P states.But the overall contrast(CR)is not significantly improved.Without PI,the white background black character cholesteric display device has higher contrast and better stability.(3)The effects of reflective infrared and ultraviolet materials on the contrast and refresh voltage of cholesteric bistable liquid crystal display devices were studied.The effects of refractive index of cholesteric liquid crystal materials on the contrast of devices and the dielectric properties of cholesteric liquid crystal materials on the refresh voltage of devices were studied.The experimental results show that the materials with infrared reflective wavelength can make the device have higher contrast and lower refresh voltage.In a certain range,the greater the refractive index of cholesteric liquid crystal materials,the higher the contrast,beyond this range,the contrast will decline,so we need to find a balance.The larger the dielectric density of cholesteric liquid crystal,the lower the refreshing voltage.(4)The effects of the structure of liquid crystal monomer on the refractive index and dielectric properties of cholesteric liquid crystals were studied.The experimental results show that the longer the chain of liquid crystal molecular structure is,the higher the refractive index and brightness point are.the more the conjugated groups of liquid crystal molecular structure are,the greater the refractive index of liquid crystal is;the more the ring structure of liquid crystal molecule is,the more the refractive index of liquid crystal molecule is.The bigger it is.The stronger the polarity of the polar Substituent group,the more the polar Substituent group,the more the vector decomposition of the polar groups tends to be in the long axis direction,and the larger the dielectric of the liquid crystal monomer.