The area occupied per surfactant molecule (Amin at theair-water interface38has been obtained by using Eq. (2)Amin= 1/N max(2)The value of the surface pressure at the cmc (cmc wasobtained from Eq. (3),cmc= o− cmc(3)where oand cmcare the values of surface tension ofwater and the surfactant solution at the cmc, respectively.The surface excess concentration (max is an effectivemeasure of adsorption at air/water interface. It measureshow much the air/solution interface has been changedby surfactant adsorption and depends on the molecularstructures of surfactants. The value of maxand Aminineach case has been calculated and is given in Table II