Adsorption kinetics of plasticizer dibutyl phthalate at the air-water interface

Although the amphipathic nature of plasticizer dibutyl phthalate (DBP) was previously verified, the adsorption kinetics of DBP at the air-water interface is yet to be ascertained. Hence, the adsorption kinetics of aqueous DBP solutions was studied by measuring the dynamic/equilibrium surface tensions (ST) and conducting theoretical simulation. A pendant bubble tensiometer was used to examine the ST relaxations of aqueous DBP solutions at different concentrations. The experimental ST data confirmed the surfactant-like nature of DBP molecules as the dynamic ST of DBP solution smoothly reduced from 72 mN/m to its respective equilibrium ST. The simulation results indicate that the Langmuir model describes very well the dynamic/equilibrium ST data of DBP. The adsorption of DBP molecules onto a freshly created air-water interface was found to be of mixed control. In addition, the adsorption and desorption rate constants of DBP were also obtained. Unlike typical surfactants, a phase separation occurred when the bulk concentration is larger than 6.0 x 10(-8) mol/cm(-3); thereby indicating the absence of micelle formation in DBP solutions. (C) 2020 Elsevier B.V. All rights reserved.