Tag Archives: National Research Foundation of Korea (NRF)

Precise color control in anti-counterfeiting technology with silver nanoparticles trapped in a polymer matrix

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A December 4, 2024 news item on phys.org announces a new anti-counterfeiting technology from South Korea, Note: A link has been removed,

In a significant advancement in the field of anti-counterfeiting technology, Professor Jiseok Lee and his research team in the School of Energy and Chemical Engineering at UNIST [Ulsan National Institute of Science and Technology] have developed a new hidden anti-counterfeiting technology, harnessing the unique properties of silver nanoparticles (AgNPs). The results are published in Advanced Materials.

“The technology we have developed holds significant promise in preventing the counterfeiting of valuable artworks and defense materials, particularly in scenarios where authenticity must be verified against potential piracy,” Professor Lee explained.

…

The original December 4, 2024 Ulsan National Institute of Science and Technology (UNIST) press release by JooHyeon Heo, which originated the news item, provides more details about the work,

Abstract
Silver nanoparticles (AgNPs) are known for their unique plasmonic colors and interaction with light, making them ideal for color printing and data encoding. Traditional methods like electron beam lithography (EBL) and focused ion beam (FIB) milling, however, suffer from low throughput and high costs. In this paper, a scalable and cost-efficient method is introduced for producing multiplexed plasmonic colors by in situ photoreducing AgNPs within microgel architectures with controlled porosity. Utilizing a digital micro-mirror device (DMD)-based flow microlithography system combined with a programmable dithering-mask technique, the high-throughput synthesis of shape or barcoded microparticles is facilitated, along with large-scale, high-resolution images embedded with hidden multiplexed plasmonic colors. This approach allows for a hidden multiplexed plasmonic color code library, significant enhancing the encoding capacity of barcode microparticles from 33 to 303 (a 1000-fold increase). Additionally, quantitative agreement is achieved between chemically encrypted and optically decrypted plasmonic colors using a deep learning classifier. Moreover, the method also supports the production of large scale (>5.6 × 5.6 cm2), high-resolution (>300 dpi) microgel arrays encrypted with multiple plasmonic colors in under 30 min. The multiplexed plasmonic coloration strategy in microgel architectures paves a new way for hidden data storage, secure optical labeling, and anti-counterfeiting technologies.

The portrait of Mookpododo—an ink on-silk painting of grapes featured on the genuine Korean ₩50,000 bill—radiates a bright fluorescent green, an effect achieved through security ink that is visible under ultraviolet (UV) light. This feature remains concealed from the naked eye and is intended for use by professionals in financial institutions and other high-security environments.

[see news item]

The team leveraged the inherent disadvantage of AgNPs, which tend to discolor upon exposure to UV light, to create a controlled color development process. By trapping silver nanoparticles within a polymer matrix, researchers can manipulate particle size and, consequently, the color emitted under UV light. Larger polymer nets yield silver nanoparticles that appear yellow, while smaller nets produce a red hue, allowing for precise control of the resultant colors based on ingredient combinations.

Using these high-molecular structures as pixels, the research team successfully crafted high-resolution color images. Utilizing an automated photo-etching technique, they reduced the fabrication time to one-tenth of traditional methods, producing an image of a parrot larger than a standard business card in just 30 minutes. This digital process allows for flawless color printing, with precise control over saturation and tone.

In addition to images, anti-counterfeiting data can be discreetly embedded in arrangements of polymer structures that resemble red, yellow, and blue barcodes. The color response varies with UV exposure time, allowing for the storage of temporal information within the barcode structure. This innovative approach enables information storage capabilities to increase over 1,000-fold compared to conventional methods, with a potential for unlimited data encoding by arranging barcode particles without additional synthesis.

To enhance the reliability of this technology, the research team developed an artificial intelligence algorithm capable of analyzing barcode authenticity. This AI system boasts a remarkable reliability rate of 98.36%, distinguishing genuine barcodes from counterfeit ones by assessing material composition, UV exposure duration, and barcode integrity.

“The simplicity of the manufacturing process and the reproducibility of colors present a substantial opportunity for the advancement of information encryption systems, particularly in anti-counterfeiting applications,” stated Byungcheon Yoo, the lead author of the study.

The groundbreaking findings from this research were published in the online version of Advanced Materials on November 20, 2024. This research was supported by the National Research Foundation of Korea (NRF).

Here’s a link to and a citation for the paper,

High-Throughput Multiplexed Plasmonic Color Encryption of Microgel Architectures via Programmable Dithering-Mask Flow Microlithography by Byungcheon Yoo, Chaeyeong Ryu, Seunghwan Lee, Sanggyun Jeong, Younghoon You, Dahye Baek, Dowon Kim, Inkyu Jeon, Ki-Seok An, Jongwon Oh, Jiseok Lee. Advanced Materials DOI: https://doi.org/10.1002/adma.202405388 First published: 20 November 2024

This paper is behind a paywall.

Cosmetics breakthrough for Ulsan National Institute of Science and Technology (UNIST)?

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Cosmetics would not have been my first thought on reading the title for the paper (“Rates of cavity filling by liquids”) produced  by scientists from Ulsan National Institute of Science and Technology (UNIST).

A September 17, 2018 news item on Nanowerk announces the research,

A research team, affiliated with Ulsan National Institute of Science and Technology (UNIST) has examined the rates of liquid penetration on rough or patterned surfaces, especially those with pores or cavities. Their findings provide important insights into the development of everyday products, including cosmetics, paints, as well as industrial applications, like enhanced oil recovery.

This study has been jointly led by Professor Dong Woog Lee and his research team in the School of Energy and Chemical Engineering at UNIST and a research team in the University of California, Santa Barbara. Published online in the July 19th issue of the Proceedings of the National Academy of Sciences (“Rates of cavity filling by liquids”), the study identifies five variables that control the cavity-filling (wetting transition) rates, required for liquids to penetrate into the cavities.

A July 26, 2018 UNIST press release (also on EurekAlert but published on September 17, 2018), which originated the news item, delves further into the work,

In the study, Professor Lee fabricated silicon wafers with cylindrical cavities of different geometries. After immersing them in bulk water, they observed the details of, and the rates associated with, water penetration into the cavities from the bulk, using bright-field and confocal fluorescence microscopy. Cylindrical cavities are like skin pores with narrow entrance and specious interior. The cavity filling generally progresses when bulk water is spread above a hydrophilic, reentrant cavity. As described in “Wetting Transition from the Cassie–Baxter State to Wenzel State”, the liquid droplet that sits on top of the textured surface with trapped air underneath will be completely absorbed by the rough surface cavities.

Their findings revealed that the cavity-filling rates are affected by the following variables: (i) the intrinsic contact angle, (ii) the concentration of dissolved air in the bulk water phase, (iii) the liquid volatility that determines the rate of capillary condensation inside the cavities, (iv) the types of surfactants, and (v) the cavity geometry.

“Our results can used in the manufacture of special-purpose cosmetic products,” says Professor Lee. “For instance, pore minimizing face primers and facial cleansers that remove sebum need to reduce the amount of dissolved air, so that they can penetrate into the pores quickly.”

On the other hand, beauty products, like sunscreens should be designed to protect the skin from harmful sun, while preventing pores clogging. Because, clogged pores hinder the skin’s function of breathing or exchange of carbon dioxide and then cause further irritation, pimples, and blemished areas on your skin. In this case, it is better to reduce volatility and increase the amount of dissolved air in the cosmetic products, as opposed to facial cleansers.

“This knowledge of how cavities under bulk water are filled and what variables control the rate of filling can provide insights into the engineering of temporarily or permanently superhydrophobic surfaces, and the designing and manufacturing of various products that are applied to rough, textured, or patterned surfaces,” says Professor Lee. “Many of the fundamental insights gained can also be applied to other liquids (e.g., oils), contact angles, and cavities or pores of different dimensions or geometries.”

This study has been supported by the National Research Foundation of Korea (NRF) grant, funded by the Ministry of Science and ICT.

Here’s a link to and a citation for the paper,

Rates of cavity filling by liquids by Dongjin Seo, Alex M. Schrader, Szu-Ying Chen, Yair Kaufman, Thomas R. Cristiani, Steven H. Page, Peter H. Koenig, Yonas Gizaw, Dong Woog Lee, and Jacob N. Israelachvili. PNAS August 7, 2018 115 (32) 8070-8075 https://doi.org/10.1073/pnas.1804437115 Published ahead of print July 19, 2018

This paper is behind a paywall.