Two-Dimensional Melts: Polymer Chains at the Air−Water Interface

Both physical surface rheology and computer simulation experiments were performed to understand the conformation of polymers in 2D systems. The interfacial stress rheometer was used to measure surface rheological properties of Langmuir monolayers of poly( tert -butyl methacrylate) with molecular weights between 81.5 and 780 kg mol -1 . The Π− A isotherms for these monolayers show two transitions: a plateau at Π ≈ 18 mN m -1 and a bend at Π ≈ 52 mN m -1 . The properties of the films are shown to be substantially different above and below the plateau surface pressure, Π p . Below Π p, the monolayers are primarily viscous, and surface viscosity increases linearly with MW, while above Π p, the films are more elastic, and surface viscosity is MW-independent. Computer simulations of these systems produce qualitatively similar Π− A isotherms. The observed transition at Π p marks the changeover from polymer chains existing in a single layer to forming regions of multilayers.