Liquid Crystal Switching Elements With Low-Haze DC Polymerisation
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Solution Overview
Problem
There is a need for switchable elements suitable for privacy windows that operate at low voltages with low energy consumption and have improved optical and electro-optical performance, along with enhanced reliability and stability.
Innovation Solution
A method involving a liquid-crystalline medium with mesogenic and chiral compounds, polymerised under a direct current (DC) electric field, to create a switching element that is operable between optically clear and scattering states, minimizing residual haze and ensuring stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polymerisation is performed without DC electric field, then manufacturing process is simpler, but residual haze increases and optical clarity deteriorates
Solution Approach 1:
The patent applies a DC electric field during the polymerisation process to pre-orient polymer chains before complete polymerisation occurs. This preliminary orientation action prevents light scattering by ensuring polymer chains align with the electric field, thereby reducing residual haze and improving optical clarity in the final product.
2Speed
If higher voltage is applied for switching, then switching speed increases, but energy consumption increases
Solution Approach 1:
The patent modifies the switching parameters by using specific voltage ranges (5-20V for clear state, 20-40V for scattering state) and controlled pulse durations (0.1-10 seconds) to achieve fast switching between states. By optimizing these parameters, the system achieves rapid state transitions while minimizing energy consumption through efficient voltage control rather than continuously high voltage.
Solution Approach 2:
The patent employs periodic voltage pulses to switch between clear and scattering states. The switching mechanism uses time-limited voltage application (0.1-10 seconds per state) rather than continuous high voltage, achieving fast switching speed while reducing overall energy consumption through periodic rather than continuous energy input.
3Reliability
If polymerisable mesogenic compounds are used in high concentration, then polymer network density increases and stability improves, but residual haze increases and optical performance deteriorates
Solution Approach 1:
The patent optimizes the concentration parameter of polymerisable mesogenic compounds to a specific range (0.1-5% by weight) and combines this with DC electric field application during polymerisation. This parameter optimization ensures sufficient polymer network density for stability while maintaining low residual haze and high optical clarity through proper molecular orientation.
Solution Approach 2:
The DC electric field is applied during polymerisation to pre-orient polymer chains formed from polymerisable mesogenic compounds. This preliminary orientation prevents random polymer network formation that would cause light scattering, thereby enabling the use of sufficient polymer concentration for stability without compromising optical clarity.
4Manufacturing precision
If AC electric field is used for polymerisation, then polymerisation proceeds uniformly, but residual haze increases compared to DC field
Solution Approach 1:
The patent inverts the conventional approach by using DC electric field instead of AC electric field for polymerisation. While AC field is traditionally used to avoid electrochemical reactions, the patent applies DC field to achieve superior optical clarity through sustained unidirectional polymer chain orientation, and manages electrochemical effects through controlled voltage and time parameters.
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 method produces switching elements with reduced residual haze, improved clarity, and enhanced reliability, allowing fast switching between states with low energy consumption and reduced pressure sensitivity, suitable for privacy windows and other applications.
Implementation Method 1
a switching element which is operable in and electrically switchable between an optically clear state and a scattering state
Implementation Method 2
polymerised under a direct current (DC) electric field
Implementation Method 3
a liquid-crystalline medium which comprises one or more mesogenic compounds, one or more chiral compounds and the one or more polymerisable mesogenic compounds
Implementation Method 4
one or more polymerisable mesogenic compounds provided in a layer containing a liquid-crystalline medium which comprises one or more mesogenic compounds, one or more chiral compounds and the one or more polymerisable mesogenic compounds are subjected to polymerisation
Data Source
AI summary
A method for preparing a switching element which is operable in and electrically switchable between an optically clear state and a scattering state, wherein one or more polymerisable mesogenic compounds provided in a layer containing a liquid-crystalline medium which comprises one or more mesogenic compounds, one or more chiral compounds and the one or more polymerisable mesogenic compounds are subjected to polymerisation in the presence of a direct current (DC) electric field in the layer. Also, a switching element obtained or respectively obtainable by carrying out the method and to the use of the switching element in a window.