Adsorption of non ionic surfactants at the solid/water interface

Reversible adsorption of non-ionic surfactants, such as alkyl (CNa ENp) or alkyl phenol polyoxyethylene glycol (CNaPENp), occurs onto hydrophilic or polar solids below the critical micellar concentration (CMC). As shown in several experimental studies, all adsorption isotherms reach a plateau around the CMC. Generally speaking, the adsorption appears to be a cooperative process involving strong lateral interaction between surfactants and weak interaction with the solid surface. In the first part of this paper, an overview of some recent experimental studies of non-ionic adsorption layer is presented, including fluorescence spectroscopy, neutron scattering and atomic force microscopy. In the second part, a theoretical discussion of the aggregative adsorption process onto hydrophilic solid/water interface is presented. This last part will permit to raise some interesting questions concerning the role of the so-called ‘normal interaction’ (surfactant/solid interaction) to select the optimal surface aggregate curvature.