jasdooit

A collaborative research group from KAIST and Seoul National University has managed to observe ‘nano-droplets,’ which are significantly smaller than the width of a human hair, for the first time globally.

Understanding how water and other liquids spread, stick, and drip across surfaces is essential for hydrogen generation catalysts, batteries, and the production of semiconductors. Nevertheless, up until now, droplets have been too tiny to track their motion directly, leading scientists to use indirect methods for estimation.

◇ What Makes Nano-Droplets Significant?

The effectiveness of hydrogen production catalysts is influenced by the speed at which droplets and bubbles descend. When droplets fail to stick to the surface and fall quickly, there is a reduced chance of bubbles causing blockages in the system.

Water surprisingly has an important role in semiconductor manufacturing. Semiconductor chips are produced through hundreds or even thousands of exact procedures. Throughout this process, tasks such as cleaning surfaces, applying chemical substances, and rinsing are common. Specifically, the last step involves rinsing with water and then drying.

If water fails to distribute evenly across the semiconductor wafer and accumulates in specific regions, dust or chemicals might not be consistently removed during the cleaning process, resulting in spots or leftover substances. If water evaporates at a slow rate, impurities can become an issue. If it dries too rapidly, residual layers or raised structures could develop.

In batteries and fuel cells, liquid reactions have a major effect on durability and performance. Batteries include electrolytes that help conduct electricity. The more uniformly the electrolyte covers the electrode surface, the more efficiently ions can move. If the electrolyte doesn’t spread evenly, it can lead to heat-related degradation. How electrolytes distribute and stay on electrodes directly influences battery life, storage capacity, and power output. Therefore, understanding how tiny droplets settle and spread is essential.

◇ How Were Tiny Droplets Detected?

Nano-droplets were previously too minute to be observed directly. Professor Seungbeom Hong’s group at KAIST and Professor Jongwoo Lim’s team at Seoul National University employed an atomic force microscope (AFM) to address this issue. A major challenge was that nano-droplets are so tiny that even minimal contact with a probe changes their shape. While being imaged, the droplets could vanish or become distorted, making it hard to record their initial structure.

The experimental material’s surface was carefully cooled to enable atmospheric moisture to naturally form ‘nano-droplets.’ The AFM was then utilized in non-contact mode to record the droplets’ original three-dimensional shapes without causing any disturbance. A Python-based algorithm was employed to determine the contact angle. This represented the first successful non-invasive observation and quantitative measurement of nano-droplet contact angles.

The group utilized this technology on the ferroelectric material LiTaO₃ (lithium tantalate). They demonstrated, for the first time worldwide, that modifying the electric polarization direction affects the contact angle of nano-droplets—a phenomenon absent in larger droplets. This also allowed for accurate examination of how nano-droplets engage with catalyst surfaces. Unlike earlier research that used indirect methods, direct observation and numerical calculations are now achievable.

Professor Hong Seung-beom from KAIST mentioned, “We have globally demonstrated for the first time that nano-sized droplets can be directly observed and their contact angles measured. Now, we are able to observe in real time how water behaves and reacts in the nano-scale environment.” The study was highlighted in the international academic publication *ACS Applied Materials & Interfaces*.

Research paper link: doi.org/10.1021/acsami.5c14404