Yushin Kanazawa

Influence of Microwaves on the Water Surface Tension

In this study, microwave irradiation was applied to hanging droplets of both water and ethylene glycol. Once the irradiation had ceased and the droplet was allowed to return to its original temperature, it was found that the surface tension of ethylene glycol returned to its original value. In contrast, the water surface tension remained well below its original value for an extended period of time. Similar observations have been reported for magnetically treated water, but this is the first time that such a lasting effect has been reported for microwave irradiation. The effect can be attributed to the unique hydrogen bonds of interfacial water molecules. While the irradiation intensities used in this study are well above those in household devices, there is certainly the potential to apply the methodology to industrial applications where the manipulation of surface tension is required without the use of chemical addition.

Convection and surface tension profiles for aqueous droplet under microwave radiation

Application of microwave irradiation for chemical processes, such as emulsification and polymerization, has been reported [1,2]. Surfactant free emulsion can be produced with the help of microwave irradiation. Surface tension is an important property for the industrial process such as foaming/defoaming, wetting/dewetting and flotation. Similarly, the interfacial tension plays crucial role in separation and mixing process of two immiscible liquids, which are important unit operations of the fundamental chemical engineering. In practice, surface and interfacial tensions are often altered by introducing surfactants. In our previous research [3,4], specific property for surface tension of water droplet with salt under microwave radiation was found. For example, lower surface tension after the radiation was measured. The formation of nano-bubble will explain this behavior. Normally, the surface tension of aqueous solution increases with the salt concentration because cation and anion collect water molecule more strongly as a solvation. However, the exact mechanism of surface tension reduction by microwave radiation is not clear. We tried not only measurement of surface tension but also convection in the droplet during microwave radiation. This study investigates the influence of microwave on surface tension of aqueous solution. Moreover, relation between the concentration, temperature and droplet shape, which are related with surface tension.

In-situ observation of convection in droplet under microwave radiation by PIV

In this study, microwave irradiation is applied to a liquid droplet and the surface tension, the circulation flow and temperature of water droplet are measured dynamically under the irradiation. The droplet was allowed to return to its original temperature after the irradiation, it was found that water surface tension remained well below its original value for an extended period of time. Surface tension reduction shown similar effect of ”impurity“ at molecular level during the microwave, and some “memory” after microwave, which might be caused by nano-bubble. On the other hand, microwave can introduce the circulation flow of higher rotation speed and will be expected to be applied for non-contact stirring method.