Course Code: CHM-DSM-351
Paper Name: Advance Materials (Minor)
Liquid crystals are a state of matter between a solid crystal and a conventional liquid. They flow like a liquid but their molecules have a certain degree of order, like a crystal.
The arrangement of rod-like molecules determines the phase of the liquid crystal:
| Phase | Molecular Arrangement | Key Characteristic |
|---|---|---|
| Nematic | Parallel but not in layers. | High directional order; easiest to manipulate with electricity. |
| Smectic | Arranged in distinct layers. | More "solid-like" than nematic; higher viscosity. |
| Cholesteric | Twisted/Spiral arrangement. | Reflects specific colors based on temperature (used in mood rings). |
LCDs work by using an electric field to "untwist" or realign nematic liquid crystals. This realignment changes how light passes through the screen, creating images.
Surfactants (Surface Active Agents) are molecules that lower the surface tension between two liquids, like oil and water.
When surfactants are added to water, they eventually form aggregates called Micelles.
CMC (Critical Micelle Concentration): The specific concentration of surfactant above which micelles spontaneously begin to form.
In a micelle, the hydrophobic tails hide in the center, while the hydrophilic heads face outward toward the water. This structure allows soap to "trap" grease and oil inside the center of the micelle and wash it away.
Q: Why are liquid crystals used in thermometers?
A: Because cholesteric liquid crystals change color as the temperature shifts, providing a visual temperature reading.
Q: What happens if the concentration of surfactant is below the CMC?
A: The molecules stay separate (monomers) and mostly sit on the surface of the water.
Q: What is the difference between Nematic and Smectic phases?
A: Nematic molecules are just parallel; Smectic molecules are parallel and organized into layers.