Probing the adsorption/desorption of amphiphilic polymers at the air-water interface during large interfacial deformations
Hydrophobically modified polymers are good candidates for the stabilization of liquid interfaces thanks to the high anchoring energy of the hydrophobic parts. In this article we probe the interfacial anchoring of a series of home-made hydrophobically modified polymers of controlled degree of grafting by studying their behavior upon large area dilations and compressions. By comparing the measured interfacial tension to the one that we expect in the case of a constant number of adsorbed monomers, we are able to deduce whether desorption or adsorption occurs during area variations. We find that the polymer chains with the longest hydrophobic grafts desorb for larger compressions than the polymers with the shortest grafts, because of their larger desorption energy. Furthermore, we observe more desorption for polymers with the highest grafting densities. We attribute this counter intuitive result to the fact that for high grafting densities, the length of the polymer loops is shorter, hence the elastic penalty upon compression is larger for these layers, leading to a faster desorption. The dilatation experiments reveal that the number of adsorbed anchors remains constant in the case of chains with low grafting density while chains with the highest degree of grafting seem to show some degree of adsorption during the dilatation. Therefore for these highly grafted chains there may be unadsorbed grafts remaining in the vicinity of the interface, which may adsorb quickly to the interface upon dilatation.