Adsorption/Migration of a Perfluorohexylated Fullerene from the Bulk to the Polymer/Air Interface

Adsorption/migration of a perfluorohexylated-C 60 (C 60 (C 6 F 13 ) 5 ) from the bulk of a polymer matrix (polystyrene) to the polymer/air interface is reported here as a tool for surface modification as well as the demonstration of a method to increase the efficiency of polymer additives. Surface activity of C 60 (C 6 F 13 ) 5 was evaluated as a function of bulk concentration, annealing temperature, and annealing time. C 60 (C 6 F 13 ) 5 is extremely surface-active in the polystyrene matrix, occupies ∼90% of the outermost ∼40 Å (XPS sampling depth), and renders a surface that is similar in wettability to a monolayer containing CF 3 groups (hexadecane contact angle data). Surface reconstruction studies were carried out by either spin-casting or the transfer of a free-standing (solid) polystyrene film onto the composite materials (the surface-active agent and polystyrene) and subsequent thermal annealing. Both approaches show similar results: migration of perfluorohexylated-C 60 from the bulk to the surface is driven by surface free energy minimization and is a function of annealing temperature, annealing time, and molecular weight of the polymer matrix. Peel tests indicate that the composite materials have good mechanical integrity.