Liquid Crystal Composition Frequency Dependence
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Solution Overview
Problem
Liquid crystal materials exhibit poor frequency dependence at low temperatures due to the inability of liquid crystal molecules to follow voltage frequency changes, leading to suboptimal display performance in TFT-LCD panels.
Innovation Solution
A liquid crystal composition comprising a compound represented by Formula I, with a mass percentage of at least 30%, along with compounds represented by Formulas II and III, which provides appropriate optical and dielectric anisotropy, low rotational viscosity, and good low-temperature solubility, enhancing frequency dependence and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the driving frequency is increased at low temperature, then the response speed of liquid crystal molecules is improved, but the molecules cannot follow the voltage frequency changes, resulting in poor display performance
Solution Approach 1:
The patent modifies the chemical structure of liquid crystal molecules by introducing specific functional groups (cyano, fluorine, alkoxy) and adjusting molecular parameters such as dipole moment and polarizability. These parameter changes optimize the balance between response speed and frequency following capability, enabling molecules to respond quickly while maintaining good frequency dependence even at low temperatures.
Solution Approach 2:
The patent employs composite liquid crystal compositions containing multiple components with different molecular structures and properties. By combining molecules with varying dielectric anisotropy, optical anisotropy, and viscosity characteristics, the composition achieves synergistic effects that improve both response speed and frequency dependence, resolving the contradiction between these two parameters.
2Reliability
If the dielectric anisotropy is increased to improve display properties, then the threshold voltage and response time are improved, but the frequency dependence deteriorates due to molecular polarization limitations
Solution Approach 1:
The patent introduces local polar groups (cyano, fluorine) at specific positions on the liquid crystal molecule structure rather than uniformly distributing polarity throughout the molecule. This local quality approach allows the molecules to maintain high dielectric anisotropy for improved display properties while preserving rotational flexibility and frequency following capability.
Solution Approach 2:
The patent systematically adjusts molecular parameters including permanent dipole moment, polarizability, and molecular shape to optimize the relationship between dielectric anisotropy and frequency dependence. By carefully controlling these parameters through structural modification, the invention achieves display properties that remain stable across different driving frequencies.
3Speed
If the rotational viscosity is decreased to improve response time, then the response speed is improved, but the low-temperature solubility and reliability are affected
Solution Approach 1:
The patent divides the liquid crystal composition into multiple components with different molecular weights and structural characteristics. This segmentation allows the mixture to maintain low rotational viscosity for fast response while individual components contribute to low-temperature solubility and overall composition stability, resolving the contradiction between response speed and low-temperature reliability.
Solution Approach 2:
The patent creates a composite liquid crystal system where components with low viscosity are combined with components that provide thermal stability and solubility. This composite approach enables the composition to achieve fast response times through reduced rotational viscosity while maintaining reliability and proper solubility characteristics at low temperatures through the synergistic contribution of multiple components.
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 liquid crystal composition achieves improved frequency dependence, optical anisotropy, and dielectric properties, resulting in better display performance across various temperatures and frequencies, particularly in FFS display mode, suitable for large-, medium-, and small-sized liquid crystal displays.
Implementation Method 1
The dielectric anisotropy of the liquid crystal materials directly affects the display properties of a liquid crystal device, including threshold voltage, response time, duty cycle, etc. The dielectric anisotropy of the liquid crystal materials mainly depends on the degree of polarization of liquid crystal molecules
Implementation Method 2
In addition, the change of the frequency of the applied voltage can change the degree of polarization of liquid crystal molecules, which makes the dielectric anisotropy of the liquid crystal vary. Furthermore, dielectric anisotropy usually has frequency dependence at low temperatures
Implementation Method 3
The liquid crystal composition of the present invention has an appropriate optical anisotropy, an appropriate dielectric anisotropy, especially a relatively low rotational viscosity
Data Source
AI summary
The present invention belongs to the technical field of liquid crystal materials, and in particular relates to a liquid crystal composition with good frequency dependence and a liquid crystal display element or liquid crystal display containing the liquid crystal composition. The liquid crystal composition of the present invention comprises a compound represented by Formula I, a compound represented by Formula II and a compound represented by Formula III, wherein the mass percentage content of the compound represented by Formula I is not less than 30%. The liquid crystal composition provided by the present invention has an appropriate optical anisotropy, an appropriate dielectric anisotropy, especially a relatively low rotational viscosity, a good low-temperature mutual solubility and a good reliability, especially good frequency dependence.