Adsorption layer characteristics of Triton surfactants: 1. Surface tension and adsorption isotherms

The adsorption of the non-ionic surfactants Triton X-45, Triton X-100, Triton X-165, and Triton X-405 can be described by a reorientation model, assuming that molar area required by adsorbed molecules depends on the surface coverage. The surface tension isotherms we measured by drop and bubble profile tensiometry, where it was shown that at low surfactant bulk concentrations, significant differences in the measured equilibrium tensions are due to depletion effects from the volume of a single drop. This difference in equilibrium surface tensions, observed between data from drop and bubble experiments, is a good tool to determine the adsorbed amount from the total mass balance. An intersection point of all surface tension isotherms at about 1 μmol/l is explained by a respective displacement of the ethylene oxide chain from the interface by the hydrocarbon chain.