Layer thicknesses are studied of adsorbed nonionic surfactants (Synperonic NPE) by means of two different techniques. Electrokinetic measurements give a thickness which depends on the electrolyte concentration at which the experiment was done. At low electrolyte concentration a limiting value is reached, corresponding to the hydrodynamic layer thickness for a specific molecular weight. Liquid film measurements give a thickness which corresponds to the hydrodynamic layer thickness as well. Therefore, at low ionic strength, the "electrokinetic thickness" should be approximately equal to the "steric thickness." This is confirmed by the experimental results in this study.
Cohen Stuart, M. A., van den Boomgaard, T., Zourab, S. M., & Lyklema, J. (1984). The layer thickness of adsorbed nonionic surfactants: Comparison between electrokinetic and film thickness methods. Colloids and Surfaces, 9, 163-172. https://doi.org/10.1016/0166-6622(84)80155-9