Surface Tension of Methylene Blue Aqueous Solution

This paper presents experimental studies of the surface tension coefficient (STC) of aqueous solutions of methylene blue (MB) in the presence of the proton-exchange polymer membrane - Nafion. The kinetics of change in the STC value of aqueous MB solutions has been established. The character of surface tension coefficient kinetics of aqueous solutions of methylene blue is caused by the presence of the membrane in the solution. Dissociation of sulfone groups and accompanying diffusion processes of MB solutions into the membrane leads to a sharp decrease in the STC value of the studied solutions. With prolonged exposure of the membrane in the solutions: for the aqueous solution of Mb
⁺
(blue solution), the STC value eventually increases by 5%, and for the reduced form of methylene blue - colorless water solution, the STC value decreases approximately by 5,2%. The result can be explained by the diffusion process of water and MB solution into the membrane surface. The STC of the solutions formed in the process of diffusion into the membrane has a significantly lower value compared to the STC of water by 20% for the Mb
⁺
-form and by 24% for the MbH°-form of MB.