A self-consistent-field analysis of the surface structure and surface tension of partially fluorinated copolymers: The influence of polymer architecture

A molecular-level self-consistent-field theory is used to analyze physical and thermodynamic properties of partially fluorinated poly(methyl methacrylate) chains in the vicinity of the polymer-vapor interface. The molecules are described on a united atom level in which the methyl ester and perfluoroalkyl esters are linked onto a C-C backbone, whereas the vapor is modeled as free volume. Replacing -OCH₃ groups by -OCH₂C₆F₁₃ groups was used to vary the chain composition/architecture. In agreement with experimental data, the degree of fluorination influences the surface tension in a nonlinear way; a small fraction of fluorinated groups leads to a relatively large drop of the surface tension. The surface characteristics also depend on various polydispersity effects. The effects of chain length, blockiness, and degree of incorporation of the fluorinated monomer were systematically analyzed. It is found that both the surface tension and surface structure are very sensitive to the degree of blockiness, leading in special cases to microphase separation of the bulk. For these microphase-separated systems a completely ordered bulk with lamellae parallel to the surface was observed.