収縮気泡表面の非平衡蒸気凝縮 : 分子動力学シミュレーション(<小特集>異相界面における諸現象の物理)

抄録

Non-equilibrium molecular dynamics computer simulation was performed to investigate phase change on the surface of a micro-scale vapor bubble in liquid which shrinks under compression. The system consists of Lennard-Jones particles as liquid and vapor, and soft-core particles as non-condensable gas inside the bubble. Without the gas, the bubble rapidly shrinks and completely collapses, after which a bubble reemerges at the same spot. The temperature and the pressure inside the bubble increases as the bubble shrinks, and reaches a maxium at the instant of collapse. In the case where the bubble contains large amount of non-condensable gas, it does not collapse but bounces back when it shrinks to a certain radius. Slight inhomogeneity of temperature and vapor composition inside the bubble is observed, which suggests a heat-up mechanism similar to the shock wave model for a single bubble sonoluminescence. The self-condensation of vapor particles is examined with a correlation function method. The condensation coefficient a on surface of a shrinking bubble without the gas was found to be only slightly larger than that of an equilibrium bubble. For a gas bubble, in contrast, a of a shrinking bubble is smaller than that of an equilibrium bubble.