A method for transforming cholesteric liquid crystals (CLCs) into spherical particles of micrometer size has been developed by a group of researchers led by Dr. Jialei He of Nagoya University’s Graduate School of Engineering.
CLCs are a sort of fluid precious stone that has a helical construction, empowering them to specifically mirror light. The researchers created an original anti-counterfeiting QR code that can only be displayed under a specific circular polarizer by combining spherical CLC particles with pigments that are readily available on the market. Advanced Optical Materials was the journal that published the findings.
CLCs are one example of how engineering can use nature. You have seen what CLCs can do if you have ever observed the iridescent wings of butterflies or the glossy coating on the exoskeletons of beetles. Once distinguished, CLCs that emulate the units that produce the shades of the exoskeletons of creepy crawlies are orchestrated in the lab on account of their strange varieties and properties, which lie among fluids and gems.
“The sample testing was especially difficult because of the softness of the samples at room temperature, which is a property inherent in CLCs. As a result, much effort was expended in determining an adequate approach to classify the samples without inflicting any damage.”
Dr. Jialei He of Nagoya University’s Graduate School of Engineering.
Especially helpful are the optical properties of CLCs. They show uncommon varieties because of their novel sub-atomic design and optical properties that lead to the particular impression of light at explicit frequencies. Long molecules that repeat themselves in the form of a helix make up CLCs. In the helix, the upward separation from where one district circles around and rehashes the same thing is known as the ‘pitch’.
The liquid crystal has a short pitch and reflects shorter wavelengths of light, resulting in blue and violet colors if the helix has repeating units that are close together. Be that as it may, those with a more drawn-out vertical space have longer frequencies, prompting red or orange tones.
To make things even more complicated, the crystal’s molecules are arranged in a helix, so the color can change depending on how the viewer looks at the helix. Therefore, depending on how the liquid crystal is viewed, an infinite number of colors are possible.
To use CLCs all the more effectively, analysts make round CLC particles. These particles are circular and remember the helix for a 3D network, with the goal that researchers can more readily control their tinge. In any case, a significant issue is size. Spherical CLC particles of 100 micrometers are produced by current methods, which are too large for most applications.
The development of QR codes that are more secure and cannot be replicated is one potential application for this research. Credit: Yukikazu Takeoka and Jialei He
Nagoya University researchers Jialei He (he/she) and Yukikazu Takeoka (he/she) used a technique called dispersion polymerization to create spherical CLC particles with a controlled particle size of a few micrometers to address this issue.
Since the examples were taken at room temperature, it was hard to find the new strategy. ” Dr. He stated, “The softness of the samples at room temperature, which is a property that is inherent to CLCs, made the sample testing a particularly challenging time.” As a result, it took a lot of work to figure out a good way to characterize the samples without harming them.”
The researchers made the CLC particles spherical with a uniform size distribution because the pitch of spherical CLCs of this size varies with the curvature of the particles. This is a monodisperse sphere.
“Unexpectedly, we discovered during the experiment that the structural color that was produced was significantly influenced by the particle size of the microspheres.” Dr. He stated, “We could produce a variety of colors depending on the particle size.” Additionally, we discovered that the coloration and thermal stability of the spherical CLC particles were enhanced by covering them with the polymer polydimethylsiloxane.”
The development of QR codes that are more secure and cannot be replicated is one potential application for this research. They could be made by exploiting an element of the CLCs called chirality. An asymmetry prevents an object or molecule from being superimposed onto its mirror image, which is known as chirality.
Combining the color of spherical CLC particles with non-chiral pigments that are commercially available could be used to create an anti-counterfeiting QR code because CLCs are chiral and have optical activity. The code must be understood when a particular round polarizer that permits the non-chiral light through, but not the chiral light of the QR code, is utilized.
“The advancement of circular CLC particles coming about because of this examination will give additional opportunities to minimally expense underlying variety capabilities that are not the same as those of regular variety materials,” said Dr. Takeoka. “As well as being an extraordinary practical shade for hostile to falsifying, it can likewise be utilized for different applications that exploit the circularly enraptured primary tone with little point reliance.”
More information: Jialei He et al, Particle Size Controlled Chiral Structural Color of Monodisperse Cholesteric Liquid Crystals Particles, Advanced Optical Materials (2023). DOI: 10.1002/adom.202300296
