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Measured average transmission of a normally white twisted nematic liquid-crystal cell, as a function of the lateral position x in the pixel. The dark line on the right-hand side is related to an increased ion concentration, the white line on the left-hand side with a decreased ion concentration.
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Liquid crystals used in electronic displays usually contain small amounts of ions that move under the influence of the varying applied electric field. It is well known that the motion of ions perpendicular to the substrates may lead to modified electric fields resulting in image sticking effects. During operation, the modulation in the director til...
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... transport have been obtained earlier. 8 The measurements are carried out on a 10 mm by 10 mm twisted nematic cell with a relatively high ion concentration. The cell has been driven with a sym- metric ac voltage 2 V, 100 Hz for 3 h. If the cell is driven at a midgray level, a dark line is observed near the edge of the pixel at the right-hand side Fig. 5. It is believed that the line is related to an enhanced ion concentration after lateral ion motion. The line appears after driving the cell for about 1 h. From the simulated speed of the positive ions 0.15 m/s, the lateral displacement after 1 h is estimated as 0.5 mm, which corresponds roughly with the size of the lines in Fig. 5. The ...
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... right-hand side Fig. 5. It is believed that the line is related to an enhanced ion concentration after lateral ion motion. The line appears after driving the cell for about 1 h. From the simulated speed of the positive ions 0.15 m/s, the lateral displacement after 1 h is estimated as 0.5 mm, which corresponds roughly with the size of the lines in Fig. 5. The mechanism of this phenomenon is completely differ- ent from previously reported image sticking effects 2,9 be- cause the ghost images are confined to the edges of the ad- dressed pixels and not homogeneous over the pixel ...
Citations
... Chemical decomposition and selfdissociation of the LC materials can also introduce ionic contamination [13]. Therefore, investigating the influence of the free ions on the LC's electrical, mechanical, and electrooptical properties [14][15][16][17][18][19][20][21] is an important area of fundamental and applied research. ...
The free-ion concentration in a nematic liquid crystal (LC) is found to be significantly reduced when gold nano-urchins (AuNUs) of 50-nm diameter are dispersed in the LC in dilute concentrations. The nano-urchins on AuNUs trap a significant amount of mobile ions, reducing the free-ion concentration in the LC media. The reduction of free ions results in a decreased rotational viscosity and accelerated electro-optic response of the LC. The study is carried out with several AuNUs concentrations in the LC, and the experimental results consistently suggest that there exists an optimal concentration of AuNUs, above which they tend to aggregate. At the optimal concentration, the ion trapping is maximum, rotational viscosity is at its lowest, and the electro-optic response is the fastest. Above this optimal AuNUs concentration, the rotational viscosity is found to increase, and consequently, the LC no longer exhibits an accelerated electro-optic response.
... Currently, investigations of dispersion of different kinds of NPs/NSs in LCs have shown great interest and importance in the field of materials science [25][26][27][28][29][30][31][32][33]. The dispersion of rGO can suppress ionic transport and reduce the ionic shielding by which ion-induced side effects can be eliminated [34][35][36][37]. Alam et al. have reported the reduction of orientational order parameters and subsequently, the reduction in I-N transition temperature for graphene dispersed LCs nanocomposite [38]. ...
Herein, a small concentration (0.05 wt %) of reduced graphene oxide is dispersed in the liquid crystalline media. Thermodynamic study shows the reduction of the transition temperature, enthalpy and entropy of the reduced graphene oxide dispersed nanocomposite. Optical study suggests the decrease of the optical bandgap of the dispersed nanocomposite as compared to that of the pure sample. Dielectric spectroscopic measurement is done for measuring the permittivity and conductivity of the pure and the dispersed samples. The value of dielectric anisotropy has decreased for the dispersed nanocomposite whereas the value of ionic (DC) conductivity of the dispersed nanocomposite has increased by 3 orders of the magnitude as compared to that of the pristine sample. The activation energy for DC conductivity has reduced in the dispersed nanocomposite which is responsible for the increment in DC conductivity of the system. The cut-off region of DC conductivity has increased in the dispersed nanocomposite. Electro-optical studies suggest the reduction of the threshold voltage for the Freedericksz transition, splay elastic constant and rotational viscosity for the dispersed nanocomposite.
... These free-ions generally come from the LC's chemical synthesis process, the LC cell's conductive electrodes [10,11], and the polyimide (PI) alignment layers [12]. Therefore, investigating the influence of the free ions on the LC's electrical, mechanical, and electro-optical properties [13][14][15][16][17][18][19][20] is an essential area of fundamental and applied research. Over the last decade, there has been another exciting direction of research which shows that the colloidal dispersion of nanomaterials, such as ferroelectric nanoparticles [21,22], titanium nanoparticles [23], carbon nanotubes [24][25][26], graphene [27][28][29][30][31][32], and fullerenes [23,33,34] in the LC can suppress the free-ion concentration significantly by the ion-trapping process. ...
The presence of excess free-ion impurities in liquid crystals (LCs) gives rise to a number of problems in the electro-optical liquid crystal displays (LCDs), e.g., slow electro-optical responses and image sticking effects. Here we experimentally present that the two-dimensional (2D) hexagonal boron nitride (h-BN) nanosheet can serve as a planar-alignment agent and as an ion-capturing agent at the same time in an electro-optic LC device. The 2D h-BN nanosheet is employed as a planar-alignment agent on one side of an LC cell, where the standard planar-aligning polyimide (PI) layer is used on the other side of the cell. The LC exhibits uniform planar-alignment in this h-BN/PI hybrid device. It is found that the free-ion impurities in the LC are significantly suppressed in this h-BN/PI hybrid cell compared to that in a standard PI/PI LC cell. The free-ion density is reduced in the hybrid cell due to the 2D h-BN nanosheet’s ion-capturing process. The reduction of ionic impurities results in an accelerated electro-optic response of the LC in the h-BN based hybrid cell—which may have potential application for faster electro-optic devices.
... These ions in PAN cells could be divided into two parts: free ions moving with the electric field and transient bound ions on the alignment layers. When the voltage induced by the bound ions was greater than the threshold voltage, image sticking would occur [42]. The free ions, however, could ...
... These ions in PAN cells could be divided into two parts: free ions moving with the electric field and transient bound ions on the alignment layers. When the voltage induced by the bound ions was greater than the threshold voltage, image sticking would occur [42]. The free ions, however, could counteract the ion electric field to reduce the occurrence of image sticking. ...
Image sticking in thin film transistor-liquid crystal displays (TFT-LCD) is related to the dielectric property of liquid crystal (LC) material. Low threshold value TFT LC materials have a weak stability and the free ions in them will be increased because of their own decomposition. In this study, the property of TFT LC material MAT-09-1284 doped with γ-Fe₂O₃ nanoparticles was investigated. The capacitances of parallel-aligned nematic LC cells and vertically aligned nematic LC cells with different doping concentrations were measured at different temperatures and frequencies. The dielectric constants perpendicular and parallel to long axis of the LC molecules ε⊥ and ε//, as well as the dielectric anisotropy Δε, were obtained. The dynamic responses and the direct current threshold voltages in parallel-aligned nematic LC cells for different doping concentrations were also measured. Although the dielectric anisotropy Δε decreased gradually with increasing temperature and frequency at the certain frequency and temperature in LC state for each concentration, the doping concentration of γ-Fe₂O₃ nanoparticles less than or equal to 0.145 wt % should be selected for maintaining dynamic response and decreasing free ions. This study has some guiding significance for improving the image sticking in TFT-LCD.
... This might be explained by that while creating LC cells, static electricity might be generated, and then purity ions in LC mixed together; as a result of this process, impurity ions were created. Normally, impurity ions moderately aect the threshold voltage and response time of NLC cells [26,27], but zinc oxide NPs in NLC might capture impurity ions and aect the electro-optical properties signicantly. This is referred to eld screening effect (FSE). ...
In this study, zinc oxide (ZnO) nanoparticles were synthesized by spray pyrolysis method. The properties of ZnO nanoparticles are determined by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and UV-vis spectroscopy. Nematic liquid crystal mixture E7 was doped with 1, 2, and 4% ZnO. We investigate electrical and optical parameters of pure and doped nematic liquid crystal mixture E7. The experiments related to voltage dependence and light transmittance of the pure and doped E7 were carried out. The values of threshold voltage, total phase retardation and birefringence are examined. The results show that doping zinc oxide nanoparticles into liquid crystal mixture E7 decreases threshold voltage significantly.
... [49][50][51][52][53][54] Understanding the ion-transport phenomenon in an LC and the principles governing their subsequent effects on the LC's electrical and electro-optical properties is active area of research. [55][56][57][58][59][60][61][62] Therefore, the results presented in this paper are important for developing novel methods of purifying LCs from excess ions without additional chemical synthesis. Our studies motivate various important questions and subsequent experiments are planned for the future to address several issues, such as understanding the separate effects of monolayer and multilayer flakes, with their different sizes, on the LC's iontransport, rotational viscosity, and electro-optic effects. ...
A small quantity of graphene, containing both monolayer and multilayer flakes, was doped in a nematic liquid crystal (LC), and the nematic electro-optic switching was found to be significantly faster in the LC + graphene hybrid than that of the pure LC. Additional studies revealed that the presence of graphene reduced the free ion concentration in the nematic media by ion-trapping process. The reduction of mobile ions in the LC was found to have subsequent impacts on the LC's conductivity and rotational viscosity, allowing the nematic director to respond quicker on switching the electric field on and off.
... 6-11 Understanding the ion transport phenomenon in an LC and the principles governing their subsequent effects on the LC's electrical and electro-optical properties is an important and active area of research. [12][13][14][15][16][17][18][19] In another direction, LCs have been exploited very effectively over the past decade to impose their long-range orientational order onto various nanoparticles. 20-24 Interestingly, the interactions between the LCs and nanomaterials are multifaceted, as the nanoparticles significantly alter some LC-properties. ...
... [6][7][8][9][10][11] Understanding the ion transport phenomenon in an LC and the principles governing their subsequent effects on the LC's electrical and electro-optical properties is an important and active area of research. [12][13][14][15][16][17][18][19] In another direction, LCs have been exploited very effectively over the past decade to impose their long-range orientational order onto various nanoparticles. [20][21][22][23][24] Interestingly, the interactions between the LCs and nanomaterials are multifaceted, as the nanoparticles significantly alter some LC-properties. ...
A small quantity of BaTiO3 ferroelectric nanoparticles (FNPs) of 50 nm diameter was doped in a nematic liquid crystal (LC), and the free ion concentration was found to be significantly reduced in the LC+FNP hybrid compared to that of the pure LC. The strong electric fields, due to the permanent dipole moment of the FNPs, trapped some mobile ions, reducing the free ion concentration in the LC media. The reduction of free ions was found to have coherent impacts on the LC's conductivity, rotational viscosity, and electric field-induced nematic switching. (C) 2014 AIP Publishing LLC.
... 6,7 The dielectric spectroscopic technique was implemented by Merck to investigate ion generation 8 and characterize the ion content in liquid crystal materials, which enables an estimation of the ion concentration and mobility. [9][10][11] Related to ion transport, theories, and simulation programs 12,13 have been developed to study the dispersive ion generation, 14 the measurement techniques for ions, 15 lateral ion transport, 16 and boundary image retention. 17 In terms of low refresh rate LCDs. ...
We show that SiOx, deposited at 5° to the interior surface of a liquid crystal cell allows for a surprisingly substantial reduction in the ion concentration of liquid crystal devices. We have investigated this effect and found that this type of film, due to its surface morphology, captures ions from the liquid crystal material. Ion adsorption on 5° SiOx film obeys the Langmuir isotherm. Experimental results shown allow estimation of the ion capturing capacity of these films to be more than an order of 10 000/mum2. These types of materials are useful for new types of very low power liquid crystal devices such as e-books.
... It is known that most liquid crystals (LCs) contain these ionic impurities in the range of 10 16 to 10 22 m À3 . 1) The ions in the LC cell moves following the external electric field and may stick to the interface between the LC and the electrode (or the alignment layer), possibly leading to image sticking. ...
A built-in potential exists in the reflective liquid-crystal-on-silicon (LCoS) microdisplay cell due to the work-function difference between the aluminum and indium-tin-oxide electrodes. As a consequence, the flicker is generated unless the dc offset voltage is applied to compensate the built-in potential. In this paper, we present the experimental result that the dc offset voltage changes with time as the display is operated and the ions are generated in the liquid crystal (LC). To understand the experimental result, we simulate the ion motion in the LCoS cell by considering both the drift and diffusion. We discuss how the ion concentration in the LC affects the screening of the internal electric field in the bulk LC region and subsequently the built-in potential in the LCoS cell. We show that for an ion concentration higher than the value required to fully compensate the initial built-in potential, the polarity of the built-in potential is changed due to the high electric field near electrodes. By matching the experimental and simulation results, we predict how the ion concentration in the LC increases as a function of operation time.
... Their mean densities were set to ρ 0− ≈ 1.5 × 10 20 m −3 and ρ 0+ ≈ 3 × 10 20 m −3 and their mobilities to µ − ≈ 3.0 × 10 −10 m 2 V −1 s −1 and µ + ≈ 1.5 × 10 −10 m 2 V −1 s −1 . Similar values have been reported elsewhere [17,24]. The exact values vary slightly in the results that follow since they are chosen to best fit the data. ...
An optical waveguide experiment was used to study the influence of dc electric fields on a hybrid aligned nematic liquid crystal cell. This dc switching differed from ac switching in two ways: first, the equilibrium states depended on the sign of the applied voltage, and second, there was transient activity over long (~100 ms) timescales. To understand both of these, a numerical model of the cell's dynamics, which included both the Ericksen–Leslie theory and a drift-diffusion model of mobile ions, has been developed. Comparing modelling with observations, we find that the transients are caused by the motion of tiny concentrations of ionic impurities, and that the sign dependence is caused by an asymmetric distribution of surface charge, rather than the flexoelectric effect.
