Describe the liquid-crystal state, in terms of molecular arrangement, and explain what happens as temperature increases.

Discuss three properties a substance should have if it is to be used in liquid-crystal displays.

(rod-shaped) molecules aligned in the same direction;

increasing temperature causes arrangement to lose its directional order/molecules to become more randomly arranged;

until normal liquid state occurs;

chemically stable so that it does not undergo reactions;

liquid-crystal phase stable over a range of temperatures so that frequent malfunctions do not occur;

molecules should be polar so the electronic current can influence direction;

there should be a rapid change in direction / fast switching speed;

Award [2 max] if no reasons are given.

Liquid-crystals were known well by many candidates. Some were ill-prepared to answer these questions.

Liquid-crystals were known well by many candidates. Some were ill-prepared to answer these questions.