Behaviors of Bubbles in Front of a Solidifying Interface

Abstract

By means of a solidifying water model, we investigated the influence of the concentration boundary layer on the behavior of fine bubbles (less than 60 μ m in diameter) near the solidifying interface. The solidifying interface of water solution was moved horizontally from the left to the right side of the solidifying cell. In the vicinity of the solidifying interface of a non-surfactant (NaCl) water solution, fine bubbles were moving upward, no matter how close they were from the solidifying interface. However, in the case of a surfactant (C 8 H 17 SO 3 Na) water solution, once the distance between bubbles and the solidifying interface was less than 90∼100 μ m, bubbles were found to move horizontally toward the solidifying interface, and then were entrapped by it. This phenomenon can be attributed to the surfactant concentration gradient inside the boundary layer, which results in a surface tension gradient around the surface of bubbles. Experimental results can be quantitatively explained fairly well with theoretical analysis.