Characterizing the glassy phase of a statistical copolymer monolayer

Monolayers of a statistical copolymer with a poly(methacrylate) chain and h ydrophilic and hydrophobic side groups are investigated at the air/water in terface. The isotherms suggest a fluid and a frozen phase. With in-situ X-r ay reflectivity the monolayer thickness is determined to be 2.5 nm or less. The shear viscosity in the fluid phase is extremely high yet can be descri bed in the framework of the free area model. However, the parameter which c haracterizes the overlap of holes available for a diffusing monomer unit is a factor of 2 higher than expected, suggesting local diffusion barriers fo rmed by nanosized clusters. In the glassy phase single-molecule fluorescenc e shows anomalous diffusion in an approximate to 140 nm cage (cf. ref 1), i ndicating that the clusters touch. The aggregates are mainly formed by the hydrophilic monomers, as both the X-ray data and the isotherms suggest.