Study On The Response Performance And Driving Technology Of Liquid Crystal With Negative Dielectric Anisotropy

Fast response is one of the most critical requirements for liquid crystal displays（LCD）,which is helpful to reduce the blurring and crosstalk of moving images.With the increasing demand for LCD screen quality,one of the urgent problems to be solved is response time.The liquid crystal（LC）with negative dielectric anisotropy（negative liquid crystal）has the advantages of fast response time,high voltage holding ratio,high clearing point and wide viewing angle.Therefore,it is of great significance to study the response performance of negative liquid crystals.In this Master’s thesis,the evaluation of the response performance of negative liquid crystal and the improvement of the rapid response display technology were explored mainly through testing the dynamic response time of negative liquid crystal,doping theγ-Fe₂O₃ nanoparticles into negative liquid crystal and the design of overvoltage and undershoot voltage driving technology.First,the dielectric and elastic constants of two kinds of negative LCs（SCL17V33L00and SCL17V28L00）at different temperatures were measured accurately by using the dual-cell capacitance model and LC cell capacitance model in the analyses of the changes in LC layer capacitance and Fréedericksz transition threshold voltage under the action of electric field.Then the rotational viscosity coefficientsγ₁ and the quality factor Fo M of them at 25°C、30°C and 35°C were obtained by performing dynamic response simulation using Visual Fortran software.The results of the Fo M differ by-0.42,-0.59,and-0.52,respectively.It can be obtained that the SCL17V28L00 has a faster response speed.Then,the isotropic maghemite single-crystal magnetic nanoparticlesγ-Fe₂O₃ were prepared by the chemical-induced transition method,and the surface morphology and cluster condition of the nanoparticles were detected and analyzed.Several different concentrations were obtained by doping them into the two kinds of negative LCs,and then the dynamic response time of them with different doping concentrations was measured.When the doping concentration is 0.272%,the response time reaches the lowest,and the rise time of the SCL17V33L00 reduces by 20.2%,and the decay time reduces by 17.2%.For the SCL17V28L00,the reduced values are 15.7%and 15.5%,respectively.Finally,the response time of the two kinds of negative LCs was measured under the conditions of undoped and doping concentration of 0.272%by combining the overvoltage and undershoot voltage driving methods.For SLC17V33L00,when a short pulse overvoltage with the pulse width 30ms and the amplitude 1.23V is applied,the improvement of rise time is the most obvious,which is reduced by 72.6%compared with that without doping and overvoltage driving.When applying a short pulse with the same pulse width and the amplitude 40m V as the undershoot voltage,the improvement of decay time is the most obvious,which is 28.6%lower than that without doping and undershoot voltage driving.For the SLC17V28L00,the improvement is most obvious when the short pulse overvoltage and undershoot voltage with the same pulse width and amplitude of1.205V and 45m V,respectively,are applied.Compared with the undoped and without overvoltage and undershoot driving,the rise time and the decay time are reduced by 75.1% and 27.9%,respectively.