Surface tension properties of aqueous solutions of disulfur betaine derivatives

Abstract

The equilibrium and dynamic surface tensions of aqueous solutions of two newly synthesized surfactants relevant to wool dyeing were studied by means of the Wilhelmy plate and a bubble method. The surfactants (Nα,Nα′-bis(N-dodecyl-N,N-dimethylglycine cystine dimethyl ester dihydrochloride) and (Nα,Nα′-bis(N-dodecyl-N,N-dimethylglycine) cystamine dihydrochloride), are double-chain and bicationic in character. Their CMCs and Langmuir adsorption equilibrium parameters were determined at 25°C. Both molecules are very efficient surfactants. Their surface tensions equilibrate in time-scales ranging from seconds to hours (concentration c=1000-2 μM). Their dynamic surface tensions under constant and pulsating area conditions indicate that there is a strong barrier to adsorption at the air-water interface. The presence of the micelles accelerates the net rate of adsorption, suggesting fast micellar dissociation.