An anti-counterfeit technique using elastic and optical properties of liquid crystals

ABSTRACT

As the diversity of information and data sources increases, anti-counterfeiting technologies become more critical in data recording, delivering goods and managing valuables. We propose a security device that can detect the denatured state or hacking of the information using liquid crystal’s elastic and optical properties: Twist is allowed in the nematic phase, but not in the smectic phase. The optical polarisation varies in the twisted liquid crystal. The information images are engraved on the photo-alignment layer by irradiating polarised UV light in smectic phase. Several images are fabricated controlling polarisation directions. The engraved images are not visible as long as the smectic is maintained. To reveal the images, heating is necessary to nematic, where the twist is allowed. Even in nematic, we can selectively display or hide images by adjusting polariser angles. This security method can show a warning message or hide an image even if hacking occurs. Cooling back to the smectic phase distorts the image and it never returns to the initial phase. Therefore, if the texture is a distorted image, we notice an improper temperature change or product hacking. These devices are inexpensive, simple to manufacture, and effective in product security.

GRAPHICAL ABSTRACT

KEYWORDS:

• Liquid crystal
• anti-counterfeiting
• optical anisotropy
• elastic property
• photo-alignment
• phase transition

Disclosure statement

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

Additional information

Funding

This work was funded by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education [NRF-2018R1D1A1B07047808, NRF-2020R1A6A1A03047771, NRF-2021R1I1A3052203].