Simultaneous measurement of flowing fluid layer and film thickness of a soap bubble using a UV−visible spectrophotometer

Abstract

In this Letter we report a method for observing Marangoni convection driven fluid flow, in various soap bubble systems, using a UV−visible spectrophotometer. We also report time-dependent simultaneous measurement of the thickness of the fluid layer and thickness of the bubble film. The measurement is based on earlier reports^1,2 of time-dependent monitoring of film thickness in a soap bubble by observing the interference maxima and minima occurring in the UV−visible region of wavelength. In the present case the interference maxima and minima due to the upward fluid flow appeared superimposed on those due to film thickness. Our observations suggest that the fluid layer thickness remains nearly constant for both vertical and horizontal bubbles even though the film thickness changes with time. The observed values of the fluid layer thickness are about 6.94 ± 0.15 μm for the vertical bubble and about 4.75 ± 0.09 μm for the horizontal bubble. Also, the intensity of the interference peaks due to Marangoni convection goes down as the film thickness reduces which indicates a possible decrease in refractive index of the fluid with time.