Organization of an amphiphilic graft copolymer at the air-water interface: A neutron reflectometry study

Graft copolymers of methyl methacrylate and ethylene oxide have been prepared with a methacrylate backbone and poly(ethylene oxide) grafts of 54 ethylene oxide units. Three copolymers with different ethylene oxide contents have been synthesized together with equivalent copolymers with deuteriomethyl methacrylate backbones. Each of these copolymers has been spread at the air-water interface and their organization investigated using neutron reflectometry. The reflectivity data have been analyzed using exact optical matrix and approximate partial structure factor methods. As the surface concentration and ethylene oxide content increases, the number of layers needed to reproduce the reflectivity data increases. The poly(ethylene oxide) grafts stretch deeper into the subphase as their areal density increases, and ideas from grafted brush layer theory have been applied to these data. Exact agreement is not obtained, and reasons for this have been cited; When the ethylene oxide content in the near surface layer is high, the partial structure factor of the water exhibits anomalous behavior.