"Just One Minute Needed! UNIST Develops Process Technology for Thin Film Production Using Only Water and Oil"

A technology has been developed that allows the production of thin films, which typically require complex processes, to be completed in just one minute using only water and oil.

The research team led by Professor Koo Kanghee from the Department of Energy and Chemical Engineering at UNIST announced on the 17th that they have developed a process technology that enables the fabrication of catalyst thin films and more using oil droplets dispersed in water.

Research team. (From top right clockwise) Professor Koo Kanghee, Researcher Seo Seunghwan (first author), Researcher Heo Jieun (first author), Researcher Lee Jooyoung. Provided by UNIST

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The developed technology works by having the nanoparticle-form thin film precursors attached to the surface of oil droplets float to the water surface and assemble there. When hydrogen peroxide is added, it is decomposed by the thin film precursor, generating bubbles. The thin film precursor adheres to these bubbles, is lifted up, and assembles on the water surface within one minute.

This process technology allows for precise control of thin film thickness from 350 micrometers (μm, 10-6m), and enables the synthesis of thin films up to 100 cm² in area using various precursors. The fabricated thin films have a porous structure, resulting in a large surface area, and exhibit not only high mechanical strength but also excellent flexibility.

Additionally, these thin films possess a dense bonding structure, allowing them to be easily transferred to substrates without damage using the lift-on method, where the substrate is floated up from beneath the water. Even when high-quality thin films are produced, they are often easily damaged during the transfer process to the substrate.

This was demonstrated through experiments in which thin films were transferred onto substrates of various shapes and materials, including those with three-dimensional patterns. In particular, they could be easily transferred onto substrates with precise patterns at the micrometer scale, enabling precise coating of the substrate.

The research team used carbon nanoparticles coated with platinum (Pt/C) as the precursor to produce a catalyst thin film, then transferred it onto a leaf and plated it with gold to create a flexible electrode. The electrode demonstrated consistent conductivity, lighting up a small bulb even after repeated bending.

Technology for single-step nanoparticle self-assembly and transferring the synthesized thin film onto a substrate.

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Professor Koo Kanghee explained, "This technology is a paradigm shift that applies Pickering emulsion, which is used in cosmetics manufacturing." Pickering emulsion is a technique that lowers interfacial energy by covering the oil-water interface directly with solid nanoparticles instead of molecular surfactants.

The research team developed a new platform based on the idea that it is energetically favorable for nanoparticles to be located at the interface of fluids, allowing these nanoparticles to spontaneously move from the oil-water interface to the air-water interface and assemble there.

Professor Koo added, "Not only is this technology highly cost-effective, but it also allows for various combinations of nanoparticles and is not limited by the substrate, making it widely applicable in the development of flexible electrodes, catalysts, and energy storage devices."

This research was published on February 4 in ACS Nano, a renowned journal in the field of nanoscience.

The research was supported by the Ministry of Science and ICT, the National Research Foundation of Korea (NRF) Nano Future Materials Original Technology Development Program, the Basic Research Laboratory Support Program, and the Excellent Young Researcher Program.

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