Tech Breakthrough: 1-Minute Thin Film via Water & Oil

Abstract

Freestanding networked nanoparticle (NP) films hold substantial potential due to their high surface areas and customizable porosities. However, NPs with high surface energies and heterogeneous sizes or shapes present considerable challenges as they tend to aggregate, compromising their structural integrities. In this study, we report the scalable fabrication of ultrathin, bicontinuous, and densely packed carbon NP films via Pickering emulsion-mediated interfacial assembly. This method enables the efficient transfer of closely packed NP networks from emulsions to air-water interface and ultimately to diverse substrates, which provides broad versatility for tailored applications. Utilizing the jamming structures of NPs at the fluid interface, we achieve precise control over film size with homogeneous thickness while minimizing material waste and facilitating recyclability. Notably, the films can be smoothly transferred to micropatterned, stretchable, and complex three-dimensional substrates, enabling the realization of robust conformal coatings. The resulting films exhibit high structural stability and flexibility, demonstrating significant potential for the design of stretchable and flexible devices.

A groundbreaking technology has been developed that enables the manufacturing of thin films, which typically require complex processes, using only water and oil in just one minute. Professor Kang Hee Ku and her research team from the School of Energy and Chemical Engineering at UNIST announced their novel process for creating catalytic thin films using oil droplets dispersed in water.

The developed technology involves a process in which nanomaterial precursors attached to the surface of oil droplets float to the surface of the water, where they assemble into a thin film. When hydrogen peroxide is added, it decomposes due to the thin film precursors, producing gas bubbles that cause the precursors to be lifted and assembled on the water surface within one minute.

This process allows for precise control of the thin film thickness, adjustable from 350 μm, and enables the synthesis of thin films covering an area of up to 100 cm² using various raw materials. The resulting thin films exhibit a porous structure with a high surface area, featuring exceptional mechanical strength and flexibility.

Additionally, these thin films have a dense binding structure that allows for easy transfer from the water surface to substrates using a lift-on method, without damage. Typically, the transfer process can lead to damage even when manufacturing high-quality thin films. This has been demonstrated through experiments involving the transfer of thin films onto substrates of various forms and materials, including those with intricate patterns at the micrometer scale, allowing for precise coating.

The research team utilized carbon nanomaterials coated with platinum (Pt/C) as raw materials to produce catalytic thin films, which were then transferred onto a leaf for gold plating to create flexible electrodes. These electrodes demonstrated consistent conductivity sufficient to power a miniature light bulb even under repeated bending.

Professor Ku explained, "This technology represents a paradigm shift utilizing Pickering emulsions, which are used in cosmetics manufacturing." Pickering emulsions lower interfacial energy by covering the interface of water and oil with solid nanoparticles (NPs) instead of using molecular surfactants. The team developed a new platform by leveraging the concept that it is energetically favorable for these NPs to spontaneously move from the oil-water interface to the air-water interface for assembly.

She further added, "The process is not only cost-effective but also allows for a range of NP combinations and is substrate-agnostic, making it applicable in the development of flexible electrodes, catalysts, and energy storage devices."

The findings of this research have been published in ACS Nano on February 4, 2025. The study was supported by the Ministry of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF) through the Nano Future Materials Development Project, Basic Research Laboratory Support Project, and Excellent Young Researcher Program.

Journal Reference

Jieun Heo, Seunghwan Seo, Juyoung Lee, Kang Hee Ku, "Scalable Fabrication of Freestanding Jammed Nanoparticle Films via Pickering Emulsion-Mediated Interfacial Assembly," ACS Nano, (2025)