DYNAMIC SURFACE-TENSION OF AQUEOUS SURFACTANT SOLUTIONS .2. PARAMETERS AT 1-S AND AT MESOEQUILIBRIUM

The dynamic behavior in surface adsorption for 15 highly purified surfactants and 1 partially purified commercial surfactant has been investigated. Parameters at 1-s surface age and at mesoequilibrium, characterizing dynamic surface tension, are defined and discussed. Surfactants that are more efficient at reducing surface tension under equilibrium conditions are more efficient at reducing it in a short time. A bulk phase surfactant concentration of at least 5 × 10-4 M is required to achieve a 1-s surface tension that does not change much with increase in surfactant concentration. A fairly good correlation between the wetting time on cotton skeins and the surface tension at 1 s (γ1s) has been found for 20 commonly used industrial and 3 purified surfactants at various concentrations. For a wetting time of 25 s or less, γ1s should be <38 mN m-1; for a wetting time of 10 s or less, <34 mN m-1. The deviation of dynamic from equilibrium properties increases with increase in the surface activity of the surfactants. Compounds with larger equilibrium maximum excess surface concentration (Γmax) values appear to require more time to reach mesoequilibrium that those with smaller Γmax values in the same surfactant class. © 1990.