Interfacial physico chemical study on engulfment and pushing of fine partcle in liquid solution by solidifying interface

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Behavior of fine bubbles in front of solidifying interface of C_8H_<17>SO_3Na water solution was directory observed under the gravity condition of μG and 1G by combining Mach-Zehnder interfernometer. Fine bubbles inside the concentration boundary layer of C_8H_<17>SO_3Na formed in front of the interface move quickly toward the interface and are engulfed by the interface. On the other hand, the bubbles outside the boundary layer, just float up under 1G or don't move under μG in the solution. The above motion of fine bubbles toward the interface can be explained reasonably based on the driving force, acting on the bubble, caused by the surface tension gradient along the bubble surface due to the concentration gradient of C_8H_<17>SO_3Na in front of the interface.Behavior of fine graphite particle in distilled water was directly observed under the gravity condition of μG and 1G. Sedimentation velocity of the particle in the water with temperature gradient was smaller than that in the water with uniform temperature under 1G gravity condition. We also observed a few graphite particles floated up in the water with temperature gradient under μG gravity condition. The temperature gradient, dT/dZ>0, where T is temperature, Z is the vertical height in the water. The above results indicates that the interfacial tension gradient along the interface between the particle and the liquid causes the motion of fine solid particle as well as fine bubble.Therefore, the behaviors of fine particles such as bubbles, liquid droplets and solid particles in front of the solidifying interface are dominantly influenced by the interfacial tension gradients caused by the gradients of concentration of surface active component and also temperature, which closely relates to the materials processing by the aid of solidification process.