Dichroic-Dye Liquid-Crystalline Media for Uniform Smart Window Dimming
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Solution Overview
Problem
There is a need for liquid-crystalline media with improved chemical, physical, and electro-optical properties, particularly for use in switching elements and window elements, that can provide effective dimming with a uniform appearance and suitable reliability and stability, especially for solar applications.
Innovation Solution
A liquid-crystalline medium comprising one or more compounds of formula I and one or more dichroic dyes, with specific alkyl chains and dye concentrations, providing broad and stable LC phase ranges, suitable for guest-host type applications, and enhancing device performance with fast and uniform switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional liquid-crystalline media are used in guest-host devices, then the devices can achieve light transmission modulation, but the contrast ratio and switching uniformity are insufficient
Solution Approach 1:
The patent modifies the chemical structure of cyanobiphenyl derivatives by introducing specific substituents (fluorine atoms at positions 3 and 5, and various end groups R1 and R2) to change the physical and electro-optical parameters of the liquid crystal medium. This structural parameter change improves both the contrast ratio and switching uniformity by optimizing the interaction between the liquid crystal molecules and dichroic dyes.
Solution Approach 2:
The patent creates a composite liquid-crystalline medium by combining modified cyanobiphenyl derivatives with dichroic dyes in specific concentrations. This composite system achieves synergistic effects where the modified cyanobiphenyl provides improved molecular alignment and the dichroic dyes provide strong light absorption, resulting in enhanced contrast ratio and switching uniformity.
2Illumination intensity
If the concentration of dichroic dyes is increased to improve contrast, then the absorption increases, but the switching uniformity and appearance homogeneity deteriorate
Solution Approach 1:
The patent optimizes the concentration parameter of dichroic dyes to a specific range (1-10 wt%, preferably 3-7 wt%) in the liquid-crystalline medium. This parameter optimization ensures sufficient light absorption for high contrast while preventing excessive dye concentration that would cause aggregation and non-uniform appearance, thus maintaining composition stability.
Solution Approach 2:
The patent introduces fluorine substituents at specific positions (3 and 5) of the cyanobiphenyl core structure, creating local regions with enhanced electron-withdrawing properties. This local modification improves the overall molecular alignment and interaction with dyes, enabling better contrast at optimized dye concentrations while maintaining uniform distribution and appearance homogeneity.
3Speed
If cyanobiphenyl derivatives are used to achieve fast switching, then the response time improves, but the phase range stability is reduced
Solution Approach 1:
The patent carefully adjusts the molecular parameters of cyanobiphenyl derivatives by selecting specific end groups (R1 and R2) and linking groups (L1 and L2) to optimize the balance between switching speed and phase range stability. The fluorine substitution at positions 3 and 5 reduces molecular weight and enhances response time, while the overall molecular structure maintains sufficient intermolecular interactions for phase stability.
Solution Approach 2:
The patent creates a composite liquid crystal mixture by combining modified cyanobiphenyl derivatives with specific dichroic dyes and co-solvents. This composite formulation achieves synergistic effects where the cyanobiphenyl provides fast switching response and the additional components broaden and stabilize the liquid crystalline phase range across different temperatures.
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 medium achieves high contrast between bright and dark states, stable switching, and reliable performance in dimmable smart windows, offering energy savings and improved comfort in buildings and vehicles.
Implementation Method 1
Devices based on the guest-host effect were first described by Heilmeier and Zanoni... In a guest-host system, the LC medium comprises one or more dichroic dyes in addition to the liquid crystal. Owing to the directional dependence of the absorption by the dye molecules, the transmissivity of the dye-doped liquid crystal to light can be modulated when the dyes change their alignment together with the liquid crystal.
Implementation Method 2
Liquid crystals are used in particular as dielectrics in display devices, wherein the optical properties of such materials can be influenced by an applied voltage.
Implementation Method 3
Owing to the directional dependence of the absorption by the dye molecules, the transmissivity of the dye-doped liquid crystal to light can be modulated when the dyes change their alignment together with the liquid crystal.
Data Source
AI summary
The present invention relates to liquid-crystalline media comprising one or more mesogenic compounds of formula I as set forth herein and one or more dichroic dyes, and to switching elements and window elements containing the LC materials. The present invention further relates to the use of the liquid-crystalline media in devices for regulating the passage of energy from an outside space into an inside space, for example in switchable windows for solar energy control in smart buildings and vehicles with energy efficiency and improved comfort.