Milky translucent haze of a large-scale topological defect array in nematic liquid crystal

ABSTRACT

A large two-dimensional (2D) topological defect array in nematic liquid crystal (NLC) shows a translucent watery hazy texture. The haze is a composition of three optical phenomena: scattering of light, lens imaging and diffraction. The scattering of light causes the milky haze. Vertically aligned NLC cells with pixel electrodes were fabricated to produce the crowded irregular defects. The key parameters are the electrode shape (pad or annulus), the array structure (square or hexagonal) and the pixel size (from $15\mu m\times 15\mu m$ to $200\mu m\times 200\mu m$). Location and topological charge of the defects are identified under a polarised optical microscope. 2D Fourier transform of the defect distribution gives the spatial frequency spectrum, which is the diffraction pattern of light through the defects. Large pad electrodes produce ordered defects and significant diffraction. Crowded irregular defects render the milky translucent haze and a continuous spatial spectrum. The traditional haze measurement is not able to distinguish the scattered and diffracted light. The spatial spectrum can accurately describe the appearance perceived by the viewers. Small annulus electrodes in a hexagonal array produce the messiest defects, the haziest texture and the most comfortable visual experience among the others.

GRAPHICAL ABSTRACT

KEYWORDS:

• Nematic liquid crystal
• topological defect
• smart window
• phase grating

Acknowledgments

We thank Dr Chien-Huang Liaw, Dr Kun-Cheng Tien and Dr Jin-An Lin from AU Optronics for all the kind support and sharing the experiences with smart windows during the author’s internship.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Additional information

Funding

This research was supported by the National Science and Technology Council (Former Ministry of Science and Technology), Taiwan, R.O.C. under Grant no. MOST 109-2112-M-009 -019 and Grant no. MOST 110-2112-M-A49 -031.