ADSORPTION-KINETICS OF OCTYLPHENYL ETHERS OF POLY(ETHYLENE GLYCOL)S ON THE SOLUTION AIR INTERFACE

We studied the dynamic surface tension of aqueous solutions of Triton X-100 and Triton X-405 by the maximum bubble pressure and the inclined plate methods in the lifetime range from 0.001 s up to 10 s. It is established that in the region of large and ultimately small surface pressure and time the adsorption follows diffusion kinetics, but in the region of intermediate values of lifetime and surface pressure both the surfactants decrease the surface tension faster than predicted by the existing diffusion theory. We offer a model that provides for the ability of poly(ethylene glycol) chains to adsorb on the water-air interface and to change the area that a molecule occupies on the surface. For this model we achieve full coincidence of the measured values and the values calculated according to the diffusion theory of the dynamic surface tension. It is ascertained that the Triton X-405 molecule can exist in the surface layer in different states: with the poly(ethylene glycol) chain fully expanded or with it partially or fully submerged in solution. The first state is most probable at surface pressures less than 5 mN m-1, and the second is probable at a pressure of about 8-10 mN m-1. At pressures larger than 15-20 mN m-1, the poly(ethylene glycol) chain is fully submerged in the solution. The Triton X-100 molecule can also expand its poly(ethylene glycol) chain at low pressures and fully submerges it in the solution at higher values of the surface pressure.