Effects of Film-Forming Conditions on Surface Properties and Structures of Diblock Copolymer with Perfluoroalkyl Side Chains

Abstract

Film-forming conditions (cast solvents and film-forming technique: casting or spin-coating) are found to regulate the surface free energy of a diblock copolymer composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA-b-PFEMA). The surface properties and structures both in the solid state and in the solution of this polymer were investigated using dynamic contact angle, X-ray photoelectron spectroscopy, X-ray diffraction, reflection-adsorption Fourier transform infrared spectroscopy, dynamic light scattering, and surface pressure measurements. The surface free energy of the PMMA-b-PFEMA film drastically changed from 7.8 to 28.4 mJ/m(2), depending on the film-forming conditions. For the film cast from the micellar solution, the surface free energy is governed by the unimers, localized at the air-solution interface. On the other hand, higher amounts of micelles with the laid perfluoroalkyl side chains were exposed on the surface of the spin-coated film, which yielded a relatively high surface free energy. These findings demonstrated a significant effect of the in-solution molecular association on the surface structures and properties of the solid. In particular, the in-solution unimers played the most important role in lowering the surface free energy of the PMMA-b-PFEMA films.