Adsorption kinetics of diazinon at the air-water interface

The adsorption kinetics of diazinon is studied by using pendant bubble tensiometry enhanced by video digitization. The relaxations in surface tension for two types of processes were measured: the adsorption onto an initially clean air-water interface and the desorption out of a suddenly compressed interface that is originally at equilibrium. The adsorption of diazinon onto a clean air-water interface is verified to be a diffusion-controlled process. A diffusion coefficient was computed by comparing these adsorption profiles with numerical solutions of the bulk surfactant diffusion equation and the Langmuir equilibrium adsorption isotherm. The reequilibration of a compressed interface agrees well with a diffusion-controlled process. Lower bounds on the kinetic constants for the sorption process are inferred for diazinon by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the desorption relaxation data. Problems of decomposition of diazinon and the sudden shrinkage of the interface for the desorption process are also discussed.