Movement of Foreign Particles in Liquid Driven by Interfacial Tension Gradient under Microgravity

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The behaviors of fine foreign particles in liquids (distilled water and silicone oil) with a vertical temperature were investigated under 1g and microgravity (10^<-5>g). In a drop experiment using a drop shaft of MGLAB in Toki city, water particles, which had kept falling down in silicone oil under 1g, came to a standstill as microgravity was reached when no temperature gradient existed in silicone oil. In contrast, water particles were found to move up after a very short stop as microgravity was reached when a positive temperature gradient was built up in silicone oil. The upwards velocity of the water particle show a tendency to increase with increasing radius of the particle and temperature gradient in the silicone oil.Analysis based on the previous study by our research group indicated that around the interface between particle and liquid, temperature gradient could result in interfacial tension gradient that propels particle in the direction of decreasing interfacial tension. The Dependencies of the particle velocity on the radius of the particle and the temperature gradient are also explained qualitatively based on the analysis using our previous study. In addition, this research also indicates that a much longer period of microgravity is needed in order to clarify more clearly the effect of interfacial tension gradient on the behavior of foreign particles in liquid. A parabolic flight experiment has much more feasibility for clarifying accurately the behavior of foreign particles in liquid for various kinds of systems.