Summary of Molecular Alignment and Device Applications

In LCD devices, liquid crystal materials are usually sandwiched between two glass substrates carrying alignment film with a gap of 1-10 pm. the influence of the alignment film on the substrates, liquid crystal molecular orientations are determined. Typical orientations are shown in Fig. 4.1.1. 

These orientations are classified into two groups. The directors of the liquid crystal molecules in the Homogeneous, Tilted and Homeotropic cases are aligned in one fixed direction, while, the director of the liquid crystal molecules in the Splay, Twist, Bend, Hybrid and Super-twisted nematic cases are not fixed in one direction. In the latter orientations, the liquid crystals are under stress. 

Homeotopic alignment is obtained by substrates coated with hydrophobic films such as silane compounds. Recently, polyimide films with hydrophobic side chains 

Pretilt angle (e) Twist (Twisted nematic) (1) Bend 

Display modes Principle Numbers of polarizers Dielectric anisotropy Molecular orientation (Initial Applied electric field) 

Twisted nematic (TN) Multi domain TN Optical rotation 2 Ae 0 Twist (=90°) — Perpendicular to substrate surface 

---