Bimesogenic Compounds for Flexoelectric LC Displays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current flexoelectric liquid crystal displays face challenges such as high driving voltage requirements, narrow phase ranges of chiral nematic materials, irreversible switching properties, and poor contrast due to unfavourable 'off-state' darkness, which are incompatible with modern LCD driving schemes.
Innovation Solution
The development of bimesogenic compounds with specific structural features, such as terminal alkyl groups and lateral dipoles, which improve alignment and maintain flexoelectric properties, are used in chiral nematic liquid crystal mixtures to induce a second nematic phase, optimizing elastic constants, flexoelectric coefficients, and dielectric anisotropy for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If chiral nematic liquid crystal materials are used for flexoelectric displays, then fast response times and good grey scale capability are achieved, but high driving voltage requirements and narrow phase ranges occur
Solution Approach 1:
The patent modifies the chemical composition and molecular structure of liquid crystal materials, specifically developing bimesogenic compounds with optimized elastic constants and dielectric anisotropy. This changes the physical parameters of the material to reduce the voltage required for flexoelectric switching while maintaining fast response times.
Solution Approach 2:
The invention uses composite liquid crystal systems comprising bimesogenic compounds combined with chiral dopants and other liquid crystal components. This composite approach allows tuning of both the flexoelectric response and the phase stability range, achieving low driving voltage and broad phase ranges simultaneously.
2Speed
If chiral nematic materials are used to achieve uniform lying helix alignment, then fast response times are obtained, but irreversible switching properties and poor off-state darkness occur
Solution Approach 1:
The patent optimizes the elastic constant ratios (particularly k33/k11) and dielectric anisotropy of the liquid crystal materials through careful molecular design of bimesogenic compounds. These parameter changes enable reversible switching by ensuring that the restoring forces are sufficient to return the helix to its original state after field removal, while maintaining fast response during switching.
3Length of moving object
If short pitch lengths are used in cholesteric liquid crystals, then uniform lying helix alignment is achieved, but narrow phase ranges and limited temperature stability occur
Solution Approach 1:
The invention employs composite formulations combining bimesogenic compounds with chiral dopants having complementary helical twisting powers. This allows independent optimization of pitch length (through chiral dopant concentration) and phase range (through host mixture composition), resolving the trade-off between short pitch and broad phase stability.
Solution Approach 2:
The patent introduces lateral dipole groups at specific positions in the bimesogenic molecular structure to locally enhance flexoelectric coefficients without significantly altering the overall pitch length. This localized modification allows maintaining short pitch for ULH alignment while improving the temperature stability of the phase range.
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
These bimesogenic compounds achieve high switching angles, fast response times, and good contrast at low temperatures with broad chiral nematic phase ranges and short pitch lengths, enabling uniform alignment without mechanical shearing and compatibility with current LCD driving schemes.
Implementation Method 1
induce a second nematic phase
Implementation Method 2
The flexoelectric effect is characterized by fast response times typically ranging from 6 μs to 100 μs
Implementation Method 3
The optical axis is rotated in the plane of the cell
Implementation Method 4
a chiral substance which is mixed with a nematic material induces a helical twist transforming the material into a chiral nematic material
Implementation Method 5
cholesteric liquid crystals having a relatively short cholesteric pitch
Implementation Method 6
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
Implementation Method 7
optimizing elastic constants, flexoelectric coefficients, and dielectric anisotropy
Data Source
AI summary
The invention relates to bimesogenic compounds of formula (I) wherein R11, R12, MG11, MG12 and CG1 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.