Question

Which type of liquid crystal has its structure twisted about the helical axis lying perpendicular to the orientation of molecules?

• A. Nematic liquid crystal
• B. Smetic liquid crystal
• C. Lytotropic liquid crystal
• D. Cholesteric liquid crystal

Hint:

Associate the term "Cholesteric" with a twisted or helical structure. This phase was first discovered in derivatives of cholesterol, which are chiral molecules, leading to this unique twisted arrangement.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Liquid crystals are states of matter that have properties between those of conventional liquids and solid crystals. They are classified based on the ordering of their molecules. This question asks to identify a specific type of liquid crystal based on its unique structural arrangement.
Step 2: Detailed Explanation:


Nematic Liquid Crystal: Molecules have long-range orientational order (they tend to point in the same direction, defined by a vector called the director) but no long-range positional order.
Smectic Liquid Crystal: Molecules have orientational order and are also arranged in well-defined layers. They have positional order in one dimension.
Cholesteric Liquid Crystal: This phase is also known as the chiral nematic phase. It is composed of chiral molecules. While molecules within a small region are oriented like in a nematic phase, the director itself rotates in a helical or twisted pattern as one moves along an axis perpendicular to the director. This twisted structure is exactly what the question describes.
Lyotropic Liquid Crystal: This classification is based on formation, not structure. These phases are formed when a mesogen is dissolved in a solvent, and the phase depends on the concentration.

Step 3: Final Answer:
The cholesteric liquid crystal is characterized by a helical structure where the molecular orientation is twisted around an axis perpendicular to the molecules.