Principle and Application of Cholesterol Liquid Crystal
I.Principle-
1.Molecular helical structure (core principle)
2. Pitch P: The thickness of molecular rotation over 360 degrees (color manifestation when matching with visible light wavelength).
Bragg reflection: selective reflection of specific wavelengths (colors), formula: λ ≈ n P (where n is the average refractive index).
2.Bistable electro-optic effect (display principle)
exhibits two stable states: planar state (bright/reflection) and **focal cone state (dark/scattering)**, which are maintained upon power-off (zero power consumption).
· Planar
In the absence of an electric field: the helix remains intact and reflects specific colored light (bright state).
· Focal Conic
Decreased pressure: spiral disorder, light scattering/transmission (dark state).
· Homeotropic
Increased voltage: helical unwinding, completely transparent.
3. Temperature/Electric Field Color Change Principle Temperature: Heating → Reduced pitch → Blue shift in reflected color; Cooling → Red shift.
Electric field: controls helical unwinding/recovery to achieve overtage/underage and color change.
4. Electronic paper/display application structure: Typical dual-substrate liquid crystal box consisting of upper and lower electrodes + cholesterol liquid crystal layer, with voltage-driven bistable switching.
II.Key Application Scenarios
1. Display Technologies: Reflective Low-Power Displays
E-paper / E-readers: Bistable + high readability in sunlight, ideal for prolonged reading. Colorization can be achieved by stacking three RGB liquid crystal layers, a more mature technology than electrophoretic displays (E-Ink).
Electronic shelf labels (ESL): Zero-power refresh, suitable for warehousing and retail scenarios. Global installed base has exceeded 100 million units.
Outdoor / Automotive Displays: Backlight-free design, remains clear and non-washout under strong light. Suitable for extreme environments such as bus stop signs and automotive sunroofs.
Flexible Displays: Compatible with plastic substrates, used in wearable devices and foldable screens.
2. Smart Materials and Architecture
Smart Dimming Windows / Films: Adjust light transmittance via voltage/temperature, reflect infrared light for energy savings. Can be used in building facades and automotive sunroofs, reducing vehicle power consumption by over 15%.
Energy-Efficient Display Glass: Integrated with solar backplanes to achieve "display + energy storage," ideal for outdoor information screens.
3. Sensing and Detection
Temperature Sensing: Helical pitch varies with temperature, causing reflected color shift. Used for temperature monitoring in food cold chains and medical devices.
Stress/Strain Sensing: Pressure changes the helical pitch, altering reflected color. Used for structural health monitoring in aviation and bridges.
Microwave/Laser Detection: Capable of modulating microwave reflection and laser intensity distribution, used for calibration in radar and laser systems.
4. Anti-Counterfeiting and Biomimetics
High-End Anti-Counterfeiting Labels: Unique circular polarization reflection characteristics, difficult to replicate. Used for authentication of banknotes and luxury goods.
Biomimetics: The colors of certain beetle shells in nature originate from cholesteric-like structures, providing inspiration for the design of biomimetic materials.