Experimental verification of the possibility of detecting nano-bubbles generated from O2 and Ar in water by using Ripplon surface Laser Light Scattering method with variable wavelength of Ripplon from 50 to 200 μm


Y. Ichikawa1 and Y. Nagasaka2

1School of Integrated Design Engineering, Keio University, Japan
2Department of System Design Engineering, Keio University, Japan

Keywords: surface properties
property: ripplon
material: nano-bubbles

Micro and nano-sized bubbles containing in water have been attracting increasing attention from wide variety of research fields because of their remarkable purification and bioactive effects. Although many application studies have been conducted, the fundamental understanding such as existence and stability of especially nano-bubbles (NBs) below a few hundred nanometer in diameter in water is still not clear. The purpose of the present study is to detect the changes of surface properties (apparent surface tension and viscosity) of NBs in water by the newly developed ripplon surface laser-light scattering apparatus. The present measurement technique is able to detect nanometer-order-amplitude surface wave usually regarded as ripplons excited by thermal fluctuations. Because this technique is able to measure nanometer-order sensitivity to surface properties, the present apparatus has the potential to detect the possible presence of NBs in the vicinity of water surface. We have observed temporal change of surface tension and viscosity of oxygen NBs in ultrapure water in a closed container by the ripplon surface laser-light scattering apparatus for 2 weeks at 25.5 oC. We also have measured surface properties of oxygen NBs in ultrapure water in atmospheric pressure to verify the pressure change in a closed container. The bubbles were generated for at least 60 minutes by using a micro and nano bubble generator. The observed apparent surface tension and viscosity of oxygen NBs in ultrapure water in a closed container was decreased up to about 12 % and was increased up to about 295 % relative to those of reference water, respectively. And, the observed changes of both apparent surface tension and viscosity of oxygen NBs in ultrapure water in atmospheric pressure was smaller than those of oxygen NBs in ultrapure water in a closed container. In addition, we have measured viscosity and density in bulk and pH of each sample to verify the possibility of changing thermal properties of oxygen NBs in ultrapure water. But, we have not observed significant differences of these properties. Furthermore, we measured surface properties of NBs in water generated from different gases such as argon and nitrogen to verify changing surface properties from dissolved oxygen with variable wavelength of ripplon from 50 to 200 μm.


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