13. Liquid crystalline systems.

Question 1

Define liquid crystal

Answer 1

is a kind of metamorphous material, derived from:

• gr. meta = between
• gr. morpho = shape

Liquid crystals (LCs) are matter in a state that has properties between those of conventional liquid and those of solid crystal.

• average interaction energy ~ small like in liquids
• long range order ~ like in crystals
• deformable
• string-like shape

BUT:** **order can be easily perturbed by

• T
• cc/polarity of solvents
• electric field

Question 2

Explain and name the 3 forms of order of LCs

Answer 2

• smetic: The smectic phase has molecules organized into layers.
• nematic: In a nematic phase, the rod-shaped organic molecules have no positional order, but they self-align to have long-range directional order with their long axes roughly parallel.
• cholesteric (only chiral molecules): This phase exhibits a twisting of the molecules perpendicular to the director, with the molecular axis parallel to the director.