Bimesogenic Compounds for Flexoelectric Display Driving Voltage Reduction
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Solution Overview
Problem
Current liquid crystal display technologies face challenges such as high driving voltage requirements, narrow phase ranges, irreversible switching properties, and poor contrast in flexoelectric modes like uniformly standing helix (USH) and uniformly lying helix (ULH), which limit their compatibility with modern LCD driving schemes and hinder the achievement of optimal viewing angles and response times.
Innovation Solution
The development of bimesogenic compounds with specific structural features, such as mesogenic groups and spacer groups, which are added to nematic liquid crystal mixtures to induce a second nematic phase, optimizing elastic constants, flexoelectric coefficients, and dielectric anisotropy, thereby improving the performance of flexoelectric devices by reducing driving voltage, enhancing switching angles, and achieving fast response times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If chiral nematic liquid crystal materials with short pitch are used to achieve uniform lying helix texture for flexoelectric displays, then fast response times and good viewing angle properties are obtained, but high driving voltage is required which is incompatible with common driving electronics
Solution Approach 1:
The patent modifies the physical and chemical parameters of the liquid crystal material by introducing bimesogenic compounds with specific structures (containing two mesogenic groups connected by spacer groups). This changes the elastic constants and flexoelectric coefficients of the material, enabling fast response times while reducing the driving voltage requirement to levels compatible with common LCD driving schemes.
Solution Approach 2:
The patent uses composite liquid crystal formulations combining bimesogenic compounds with conventional nematic liquid crystal materials. The bimesogenic compounds (containing two mesogenic groups) are mixed with standard nematic materials to create a composite system that exhibits both fast response characteristics and low driving voltage requirements, resolving the contradiction between speed and energy consumption.
2Adaptability or versatility
If conventional nematic liquid crystal materials are used, then compatibility with common driving electronics is achieved, but narrow phase ranges and poor contrast are observed in flexoelectric modes
Solution Approach 1:
The patent changes the material parameters by incorporating bimesogenic compounds that broaden the nematic phase temperature range and enhance the dielectric anisotropy. This improves the reliability of flexoelectric displays by providing stable operation over wider temperature ranges and achieving better contrast ratios, while maintaining compatibility with standard driving schemes.
Solution Approach 2:
The patent introduces specific local structural features into the liquid crystal material through bimesogenic compounds with particular mesogenic group configurations and spacer group lengths. These local structural modifications optimize the elastic constants and flexoelectric coefficients at the molecular level, resulting in improved overall device performance including broader phase ranges and enhanced contrast.
3Reliability
If bimesogenic compounds with specific structural features are added to nematic liquid crystal mixtures, then broad chiral nematic phases and high elastic constants are achieved, but complex synthesis and purification processes are required
Solution Approach 1:
The patent segments the liquid crystal material system into distinct functional components: bimesogenic compounds providing specific mesomorphic properties and conventional nematic materials providing baseline performance. This segmentation allows for modular optimization where the bimesogenic compounds can be synthesized and characterized separately, then mixed with commercial nematic materials, simplifying the overall manufacturing process while achieving superior material properties.
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 use of these bimesogenic compounds in chiral nematic liquid crystal mixtures results in low melting points, broad chiral nematic phases, high elastic constants, and high flexoelectric coefficients, enabling uniform alignment, improved contrast, and fast response times at low temperatures, making them suitable for advanced flexoelectric displays.
Implementation Method 1
The term 'liquid crystal', 'mesomorphic compound' or 'mesogenic compound' (also shortly referred to as 'mesogen') means a compound that under suitable conditions of temperature, pressure and concentration can exist as a mesophase (nematic, smectic, etc.) or in particular as a LC phase
Implementation Method 2
a chiral substance which is mixed with a nematic material induces a helical twist transforming the material into a chiral nematic material, which is equivalent to a cholesteric material
Implementation Method 3
The term 'chiral' in general is used to describe an object that is non-superimposable on its mirror image
Implementation Method 4
If an electrical field is applied to this configuration normal to the helical axis the optical axis is rotated in the plane of the cell, similar as the director of a ferroelectric liquid crystal rotate as in a surface stabilized ferroelectric liquid crystal display. The flexoelectric effect is characterized by fast response times
Implementation Method 5
The field induces a splay bend structure in the director which is accommodated by a tilt in the optical axis
Implementation Method 6
The optical effect is best seen when the liquid crystal cell is placed between crossed polarizers with the optical axis in the unpowered state at an angle of 22.5° to the absorption axis of one of the polarizers
Data Source
AI summary
The invention relates to bimesogenic compounds of formula I, wherein R11, R12, MG11, MG12, X11, X12 and Sp1 have the meaning given in claim 1, to the use of bimesogenic compounds of formula I in liquid crystal media and particular to flexoelectric liquid crystal devices comprising a liquid crystal medium according to the present invention.