Study on liquid-gas interface at nanoscale using transmission electron microscopy

Control for the bubble nucleation at the onset of nucleate boiling (ONB) ensures the stable start of boiling heat transfer. However, the bubble nucleation mechanism at the ONB remains unclear, because of the difficulty of in-situ observation, which is due to the small size of nucleation. Thus, in order to break through the current technological barrier of boiling heat transfer, a new experimental technique enabling the investigation of the dynamics of bubbles near the solid-liquid interface is highly desirable. Liquid cell electron microscopy is the most useful method for the in-situ observation of liquid samples at the nanoscale. We prepared a closed liquid cell fabricated using MEMS technology and observed the generation and growth of bubbles at the nanoscale and in real time using transmission electron microscopy (TEM). In the growing process, the water meniscus between smaller bubbles becomes thinner and thinner and eventually ruptures. However, when the bubbles grow, the meniscus between larger bubbles do not rupture and the bubble overlaps with others, suggesting that thin meniscus can be stable only in the case of larger bubbles because of the difference of the curvature of their liquid-gas interfaces between smaller bubbles and larger bubbles. Our experimental results lead to the insight of the mechanism of the stability and the phase change phenomena at the liquid-gas interface at the nanoscale.