Electronically Controlled Grating Based On Chiral Ion Doped Liquid Crystal

Liquid crystal is a condensed matter between liquid and crystal,so it has both liquid fluidity and crystal anisotropy.The current research mainly focuses on controlling the domain structure by using the external field.The period of the obtained domain is mostly in the micron scale,and the morphology of the domain can be controlled by regulating the intensity and distribution of the external field.These unique properties make the liquid crystal domain structure have great potential for application in the future optical information processing.In fact,liquid crystal can be seen everywhere in daily life.With the advent of the optical information age,liquid crystal materials will become more widely used.In this dissertation,we doped chiral ionic liquid in nematic liquid crystal to form cholesteric liquid crystal,and self-assembled liquid crystal grating was formed under the action of external field.The grating period can reach the order of micron,which can be clearly observed under the polarizing optical microscope.It is found that the doping concentration of chiral ionic liquid,the thickness of the liquid crystal cell,the frequency of AC voltage,the temperature of the heating stage and the amplitude of the DC bias voltage,and the different orientations of the surface of the liquid crystal cell substrate all affect the morphology of the grating.In this dissertation,we doped the chiral ionic liquid into the positive nematic liquid crystal E7 and the negative liquid crystal BHR2100-200 to study the change of the morphology of the liquid crystal grating when changing the external conditions.1.Chiral ionic liquid doped into nematic liquid crystal E7???>0?;Mix the nematic liquid crystal E7 with chiral ionic liquid in a certain proportion and then pour it into the liquid crystal cell with double-sided arrangement.Observe the changes in grating morphology when the external conditions change under a polarizing optical microscope,and observe the diffraction characteristics of the corresponding liquid crystal grating by the 633nm diffraction optical path when the temperature of the heating stage where the liquid crystal cell is located increases.The experiment found that when other conditions remained unchanged,the grating period would decrease when the concentration of the chiral ionic liquid doped into nematic liquid E7 increased,they are an inverse relationship.And there is a certain relationship between the direction of the liquid crystal grating and the doping concentration of the chiral ionic liquid.When the concentration of the chiral ionic liquid is constant,the thickness of the liquid crystal cell increases,so does the period of the liquid crystal grating.The period of the liquid crystal grating is proportional to the cell thickness,and the thickness of the liquid crystal cell also affects the direction of the grating.When the concentration of the chiral ionic liquid and the thickness of the liquid crystal cell are constant,the grating period decreases with the increase of the AC signal frequency.When the temperature of the heating stage is increased,the grating period increases as the temperature increases.There is a proportional relationship between the two.A similar grating structure can also be observed by filling the sample into a hybird aligned liquid crystal cell.When changing the frequency of the AC signal applied to the liquid crystal cell,the grating period gradually decreases with the increasing frequency.2.Chiral ionic liquid doped into negative liquid crystal???<0?;Mix negative liquid crystal with the chiral ionic liquid according to a certain proportion and then pour it into the double-sided vertical liquid crystal cell.The low-frequency AC voltage is initially applied to the liquid crystal cell.When the effective voltage value exceeds the threshold voltage,the structure of the liquid crystal grating is observed under the polarizing optical microscope,and the DC bias signal is superimposed on the low-frequency AC signal.When increasing the DC bias voltage amplitude,the grating period decreases gradually;The sample is poured into the liquid crystal cell,apply low frequency AC voltage to the liquid crystal cell,when the effective voltage value is greater than the threshold voltage.The angle formed by the direction of the grating and the initial direction n₀of the director of the liquid crystal molecules under a polarizing optical microscope is about 30°,continue to power on the liquid crystal cell,the grating rotates clockwise,and finally the direction of the grating is perpendicular to the initial direction n₀of the director of the liquid crystal molecule.When chiral ionic liquid is doped into positive nematic liquid crystal,the size and direction of the grating period can be adjusted by adjusting the chiral ionic liquid doping concentration,the thickness of the liquid crystal cell,the temperature of the heating stage and the frequency of the AC voltage.When the chiral ionic liquid is doped into negative liquid crystal,the grating morphology can be adjusted by adjusting the intensity and distribution of the external field.When the boundary condition of the liquid crystal cell is changed,the liquid crystal grating can rotate clockwise under the action of an electric field,and the direction of the grating can be adjusted.The electronically controlled grating based on chiral ion doping is sample to operate,does not require special electrode treatment,and has low driving voltage,and can adjust the grating period arbitrarily by changing the external conditions,which is highly practical.Chiral ionic liquid has many potentials in the future field of adjustable liquid crystal gratings because of their excellent solvent properties and chiral properties.