Visible spectroscopic observation of controlled fluid flow up along a soap bubble film from a pool of solution

Abstract

In this paper we report the demonstration of controlled fluid movement up along a soap bubble film from a solution on which the bubble floats. The control is achieved by controlling the gradient in surfactant concentration present in the bubble film and the solution below. We monitored the fluid flow by following the time-dependent visible absorption spectrum of a Rhodamine dye in the film that moved from the solution to the film due to fluid flow. Our observations suggest that an initial surfactant concentration gradient between the film and the solution (the solution having higher concentration) induces upward flow of fluid. Increase in the concentration gradient increases the rate of flow. No fluid flow was observed when the concentration gradient was zero or lower. In addition, our observation indicates that the upward movement of fluid occurs in concurrence with drainage of the film.