Aggregation behavior of star-shaped fluoropolymers containing polyhedral oligomeric silsesquioxane (POSS) at the air–water interface

Aggregation behavior of three star-shaped fluoropolymers containing polyhedral oligomeric silsesquioxane (POSS) and different monomers poly(methyl methacrylate) (PMMA), poly(trifluoroethyl methacrylate) (PTFEMA) and poly[poly(ethylene glycol)methyl ether methacrylate] (PMPEGMA), POSS-(PMMA-b-PTFEMA)₈, POSS-(PTFEMA-b-PMMA)₈, and POSS-(PTFEMA-b-PMPEGMA)₈) was investigated at the air–water interface. The interfacial rheology and surface morphology were studied through surface pressure and compression modulus measurements, hysteresis, relaxation, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The surface pressure–mean molecular area (Π-MMA) isotherms exhibited four regions, and it was found that the pseudoplateau observed corresponds to a “pancake-to-brush” transition. The compression modulus isotherms showed two peak values which were related to the phase transition of the monolayer. The hysteresis behaviors were compared in two different regions during the compression–expansion process. In addition, the relaxation of the monolayer was discussed using the step compression method. The relaxation process was proposed that related to the adsorption–desorption exchange of molecules and polymer segments on the surface (fast relaxation process) and the reconformation of the adsorbed macromolecules inside the adsorption layer (slow relaxation process). Furthermore, the Langmuir–Blodgett (LB) films prepared at different surface pressures from the three copolymers were scanned by AFM and a variety of morphologies were observed. Finally, the structure evolutions for the three star-shaped copolymers that aggregate at the air–water interface were proposed.