Pre-seminar Material: Molecules for Liquid Crystals Display

Speaker: Prof. Wai Kin CHAN, University of Hong Kong

Curriculum Link

• Seminar builds on knowledge from DSE curriculum:
  • Chemistry: Topic XIV Liquid Crystals

States of Matter

• Matter exists in three states: solid, liquid, and gas.

• Liquid Crystals:

  • Do not fit into the traditional three states.
  • Exhibit properties between liquid and solid crystal.
  • Considered as the 4th state of matter.

  Transition: Solid → Liquid crystal → Liquid (with increasing temperature)

Structural Properties of Liquid Crystals

• Positional Order: Regular arrangement of molecules.
• Directional Order: Molecules point in the same general direction.

Pictorial Representations

• Depictions of solid, liquid crystal, and liquid show differences in molecular arrangement and direction.

Molecular Characteristics of Liquid Crystals

• Typically rod-shaped.
• Have uneven electron distribution causing intermolecular forces, aligning molecules directionally.

Examples of Liquid Crystals:

• Cholesteryl Myristate
• Cholesteryl Benzoate

Effect of Electric Field on Orientation of Liquid Crystal Molecules

• Without Electric Field: Molecules are randomly oriented.
• With Electric Field: Molecules align along the field.

Liquid Crystals and Plane-Polarised Light

• Ordinary White Light: Vibrates in all directions perpendicular to travel.

• Polariser: Transmits light vibrating in one plane, creating plane-polarised light.

• Liquid Crystals as Polarisers:

  • Allow plane-polarised light to pass through another parallel polariser.
  • If polarisers are perpendicular, light is absorbed.

How Liquid Crystal Displays (LCD) Work

• OFF State:

  • Polariser, electrode, and reflector align to reflect light, making the panel appear bright.

• ON State:

  • Misalignment prevents light passage, making the panel appear dark.

For detailed working principles and applications of LCD, refer to the seminar.

Glossary

• Liquid Crystal Display
• Positional Order
• Directional Order
• Rod-shaped
• Cathode Ray Tube
• Cholesteryl Benzoate
• Cholesteryl Myristate
• Phosphorescence
• Polariser
• Reflector
• Light Emitting Diode

EDB Glossary Link: EDB Glossary (Chinese/English)