A4 Liquid Crystals (LCs)

Liquid crystals or LCs are fluids that have physical properties* that depend on the orientation of their molecules on some fixed axis in the material (*electrical, optical, elasticity).
The molecules LCs are often rod-shaped and polar and they generally point in the same direction. They remain pointing in one direction when the LC flows.
  • Thermotropic LC materials are pure substances that show LC behaviour over a range of temperatures.
  • Lyotropic LC are solutions that show LC state over a certain range of concentrations.
  • Nematic LC phase is characterised by rod-shaped molecules (like straws or dry spaghetti) which are randomly distributed but, on average, align themselves in one direction.
Figure 4.1 Liquid crystals
Figure 4.1 shows three examples:
  • Thermotropic: like dry, uncooked spaghetti. All tightly packed, aligned.
  • Nematic: Loosely packed spaghetti, random, same direction.
  • Random: Like a lot of spaghetti dropped on a table. No crystallinity, all directions.