Experimental evidence of the existence of non-equilibrium coverages over the surface of the floating bubble

According to earlier theoretical works, viscous drag over the surface of a floating bubble causes the top part of the bubble to have a surface coverage which is lower than the equilibrium one. This paper reports measurements of average lifetimes of single bubbles at the free surface of n-nonanol solutions located close to and far away from the point of the bubbles' formation. It was found that the average lifetimes on bubbles at free surfaces located far away were shorter than the lifetimes at the interface located close to the capillary orifice. Shorter bubble lifetimes at the interface far away from the point of the bubbles' formation show that the bubble motion indeed causes the lowering of n-nonanol surface coverage at the top pole of the floating bubbles.