Surface and interfacial tension reduction

The surface activity of surfactant is one of the most commonly measured properties and can be quantified by the Gibbs adsorption equation  

If the surface or interfacial tension is reduced with the addition of a solute (surfactant), V is positive (concentration of the solute at the solution surface is higher than that in the bulk liquid). If the surface tension is elevated with the addition of a solute (such as K2C03), F is negative (concentration of the solute at the solution surface is lower than that in the bulk liquid). 

For dilute solution (10 2 M or less) containing one ionic surfactant that completely dissociates (A 1 B ), the Gibbs adsorption equation is  

For the mixture of non-ionic and ionic surfactants in water with no electrolyte, the coefficient decreases from 2 to 1 with a decrease in the ionic surfactant concentration at the interface [ 12]. For the ionic surfactant solution in the presence of electrolyte such as NaCl, KC1, NaBr and KBr [ 13-15] the Gibbs adsorption equation is  

For the ionic surfactant solution in the presence of electrolyte containing non-surfactant counterion, the surface activity can be quantified with eqn 2.4. The more complicated Gibbs 

---