Surfactant Enhanced Spreading: Catanionic Mixture

• A freshly prepared mixture of SDeS and DoTAB wets completely polyethylene.
• The initial spreading rate is similar to that of superspreaders.
• The surface tension above CMC increases with time due to crystallisation.
• The wetting film after complete wetting assembles back into a droplet again.
• Transition from complete to partial wetting is due to crystal growth.

The spreading behaviour of aqueous solutions of mixture of two surfactants sodium 1-decane sulfonate and dodecyltrimethylammonium bromide is investigated on two hydrophobic substrates. The solutions demonstrate rapid complete wetting on polyethylene film and only partial wetting on silanized glass. It is shown that the spreading behaviour depends crucially on the age of the mixture and is determined by the crystal growth affecting the surface tension of solution. An increase of surface tension with time results in an interesting phenomenon — a transition from complete to partial wetting, that is, a droplet of freshly prepared mixture first spreads completely but after some time the solution assembles into the droplet again.

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