Adsorption of cationic/nonionic surfactant mixtures on polyester

Experiments were performed to characterize the adsorption of the cationic surfactant benzalkonium chloride (BZK) on polyester as well as measure the effect of the cationic surfactant on polyester surface charge. Additional studies were performed to examine the effect of adding nonionic surfactants on surface charge. In studies of adsorption of BZK on polyester, different behaviors were observed at pH values 6 and 10, with adsorption reaching a maximum at pH 10 but not at pH 6. In probing the zeta potential and isoelectric point (IEP) of polyester exposed to solutions composed of BZK (cationic surfactant) and an ethoxylated alcohol (nonionic surfactant), it was seen that the IEP could be shifted to higher pH levels by increasing the mole fraction of nonionic surfactant in a cationic/nonionic surfactant solution. A maximum in the IEP was obtained at a certain mole fraction for most cases. The shift in the IEP was hypothesized to be driven by increased deposition of the cationic, since the nonionic itself did not significantly change the IEP. The cooperative interactions between cationic and nonionic species were theorized to be driven not so much by attractive interactions, but other interactions, such as minimization of cationic charge repulsion.