Nematic Liquid Crystal Composition for Fast VA Display Response
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Solution Overview
Problem
Liquid crystal compositions for VA display mode struggle to achieve low viscosity and high negative dielectric anisotropy without compromising refractive index anisotropy and nematic-isotropic liquid phase transition temperature, leading to unsatisfactory response speed and display defects.
Innovation Solution
A liquid crystal composition combining specific biphenyl derivatives and fluorobenzene derivatives, with compounds represented by formulas (I), (II), and (III), optimized in content and structure to achieve low viscosity and high negative dielectric anisotropy, ensuring fast response and minimizing display defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a liquid crystal composition containing compounds with negative dielectric anisotropy is used to achieve fast response, then response speed is improved, but viscosity becomes too high
Solution Approach 1:
The patent uses a composite liquid crystal composition containing four specific compounds (formulae I-IV) with different molecular structures and properties. By combining these compounds in specific ratios, the composition achieves both low viscosity (fast response) and appropriate dielectric anisotropy, resolving the contradiction between response speed and viscosity that plagues single-component or simpler mixtures
Solution Approach 2:
The patent systematically adjusts the molecular parameters of the liquid crystal compounds, specifically the carbon atom counts in alkyl and alkenyl groups (specified ranges for each formula), to optimize the balance between viscosity and dielectric anisotropy. By changing these structural parameters within defined ranges, the composition achieves simultaneous improvement in response speed while maintaining acceptable viscosity levels
2Strength
If the content of compound (I) with low vapor pressure is increased to achieve high Δn, then refractive index anisotropy is improved, but viscosity increases and upper limit temperature decreases
Solution Approach 1:
The patent combines compound (I) with three other specific compounds (formulae II-IV) to create a balanced composite system. This composite approach allows achieving high Δn through compound (I) while the other compounds contribute to maintaining low viscosity and appropriate upper limit temperature, preventing the adverse effects of using compound (I) alone or in simple mixtures
Solution Approach 2:
The patent specifies precise ranges for the carbon atom counts in the substituent groups of all four compounds to optimize the contribution of compound (I) to Δn while controlling its negative impact on viscosity and temperature range. By adjusting these molecular parameters, the composition achieves high refractive index anisotropy without the usual penalty of increased viscosity
3Speed
If liquid crystal composition is optimized for low viscosity to achieve fast response, then response speed is improved, but dielectric anisotropy becomes insufficient
Solution Approach 1:
The patent designs a composite composition where each of the four compounds contributes different properties: some compounds provide low viscosity for fast response, while others provide appropriate dielectric anisotropy. The synergistic combination in specific ratios achieves both low viscosity and sufficient negative dielectric anisotropy, resolving the contradiction between response speed and electrical performance
Solution Approach 2:
The patent adjusts the molecular parameters of all four compounds, particularly the length and branching of alkyl and alkenyl chains, to control the balance between viscosity and dielectric anisotropy. By optimizing these structural parameters, the composition achieves fast response through low viscosity while maintaining the necessary negative dielectric anisotropy for proper display operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves satisfactorily low viscosity and high negative dielectric anisotropy without reducing refractive index anisotropy or nematic-isotropic liquid phase transition temperature, resulting in fast response and suppression of display defects in VA mode liquid crystal display devices.
Implementation Method 1
a liquid crystal material exhibiting a negative value of dielectric anisotropy (Δ∈)... using a liquid crystal composition having negative Δ∈
Implementation Method 2
adjust Δn of a liquid crystal composition within a proper range according to the cell gap... setting of Δn×d which is the product of refractive index anisotropy (Δn) and a cell gap (d)
Data Source
AI summary
A liquid crystal composition of the present invention is used for a liquid crystal display device of an active matrix driving mode which is required to have fast response. The liquid crystal composition has negative dielectric anisotropy, a large absolute value thereof, and low viscosity. Also, the liquid crystal composition has excellent liquid crystallinity that does not decrease Δn and Tni, and the like, and exhibits a stable liquid crystal phase within a wide temperature range. Further, the liquid crystal composition is chemically stable to heat, light, water, and the like and is thus suitable for use in a liquid crystal display device in which display defects are suppressed in large-size application requiring high reliability. A liquid crystal display device using the liquid crystal composition can be suitably used as a liquid crystal display device of a VA mode or the like.