Free energy in vertically aligned liquid crystal mode

ABSTRACT

Vertical alignment (VA) is a widely applied operation mode for liquid crystal displays. To achieve optimum brightness, the electrode of VA is often patterned with fish-bone fine slits to generate fringe field, so the negative liquid crystal aligns along the fine slits when the electric field is applied. VA is usually simply modelled by the bend geometry along the cell gap. However, defects, domain boundaries and periodical splay induced by the fine slits also exist in real pixels and disturb the liquid crystal alignment. Polymer-stabilised VA test cells with various fine slit pitches which lead to various strength of fringe field were fabricated to observe the deformation of liquid crystal. Then the models of liquid crystal deformation nearby the defects and in the fine slit area were proposed to calculate the electromagnetic (f_EM) and elastic free energy (f_elastic). The results show that the key factor to regulate f_EM and f_elastic is the pitch of the fine slits, and the optimum liquid crystal alignment is obtained when f_EM and f_elastic are equal. The models are useful for further investigation on the dynamics of liquid crystal alignment and applications in industrial products.

GRAPHICAL ABSTRACT

KEYWORDS:

• Liquid crystal
• vertical alignment
• free energy
• elasticity
• defect

SUBJECT CLASSIFICATION CODES:

• applied physics
• physics of liquid crystal

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Extrapolation length is a factor to estimate the range of effectiveness of the surface anchor [23]. It is calculated by the ratio of elastic constant (K) and anchoring energy (W). The numbers applied in this research are K/W = 15 pN/(3 × 10⁴ J/m²) = 50 nm. The reference for the W of PSVA is from Reference [24].