Association of cationic surfactants to humic acid (original) (raw)

2006, Colloids and Surfaces A: Physicochemical and Engineering Aspects

Surface properties of aqueous solutions of mixtures of humic acid, HA, and a series of cationic surfactants, C n TAB, have been studied. For a fixed amount of HA, the concentration of surfactant at which micelle-like aggregates are formed, cac, were determined. The log(cac) varies with the number of carbon atoms in the surfactant alkyl chain in a way similar to that shown by the log(cmc) of the pure surfactants. The addition of small amounts of C n TAB to an aqueous solution of HA has a huge effect on the surface tension decrease of water. This enhancement of the surface activity exhibited by mixtures of HA and C n TAB is explained in terms of the efficiency and effectiveness of surface adsorption. These parameters were determined by measuring the values of pC 20 , and the excess surface concentration Γ , respectively. The values of the standard free energy of adsorption, G • ad , were also determined as a function of the surfactant chain length, and from this relation the contribution by methylene group was determined.