Dr. Yuki Araki, Prof. Toyoko Arai (Graduate School of Natural Science and Technology, Kanazawa University) and Dr. Taketoshi Minato (Institute for Molecular Science, National Institutes of Natural Sciences) have successfully visualized the behavior of nanometer-sized water droplets on glass surfaces.
By observing the wetting process of silica glass in a humid air using frequency modulation atomic force microscopy (FM-AFM) (※1), they discovered that these nanoscale droplets, or “nano-water droplets”, form spontaneously with increasing humidity. Contrary to previous wetting models, these droplets do not grow larger but maintain their droplet state even in high humidity environment. Further measurements using peak force tapping atomic force microscopy (PFT-AFM) (※2) revealed that the nano-water droplets form not directly on the glass surface, but atop a gel-like layer on the glass. The visualization of these nano-water droplets provided insight into their unique movements across the glass surface, different from those of larger droplets, and suggested their potential role in mass transport on solid surfaces and involvement in various phenomena such as catalysis. The team plans to further explore the formation mechanisms of these droplets to determine if this phenomenon is universal across other materials as well.
The findings were published in the online edition of『 Scientific Reports 』on May 10, 2024.
Figure 1: Nano-water droplets formed on glass.
They were observed above 50% RH, and disappeared when the humidity was reduced to around 30%. All scale bars represent 500 nm.
? 2024 Araki, et al., Scientific Reports, CC BY 4.0
(http://creativecommons.org/licenses/by/4.0/)
?
※1：Frequency modulation atomic force microscopy (FM-AFM)
Atomic force microscopy (AFM) is a type of microscope that enables the observation of surface structures at atomic resolution. This method involves scanning the sample surface with a sharp probe and detecting variations in the cantilever’s vibrations caused by the forces between the probe and the sample using frequency modulation (FM) techniques. This approach not only allows for high-resolution observation of solid surfaces but also facilitates the study of the structure of water adsorbed on these surfaces, known as hydration structure.
※2：Peak force tapping atomic force microscopy (PFT-AFM)
PFT is a type of atomic force microscopy where the probe approaches and retracts from the sample surface while measuring the force exerted on the probe during approach and retraction. By detecting extremely small forces in the piconewton (pN) range, this technique allows for the creation of the maps of adhesion force and elastic modulus of the sample surface.
Click here to see the press release【Japanese only】
Journal：Scientific Reports
Researcher's Information: Yuki Araki
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