Surface Structure of Spin-Coated Fluorinated Polymers Films Dominated by Corresponding Film-Formation Solution/Air Interface Structure

Abstract

In this paper, the relationship between the surface structures of spin-coated fluorinated polymer films and their corresponding film-formation solution/air interface structures was investigated. Film-forming poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (FMA; PFMAy-ec-PnAMAx-ec-PFMAy) was synthesized via a controlled/living atom-transfer radical polymerization (ATRP) technique. The structures both at solution interface and on the spin-coated film surface for these polymers were studied by X-ray photoelectron spectroscopy (XPS), sum frequency spectroscopy (SFG), and surface tension measurements. The results showed that, with increasing polymerization degree of PnAMA, the fluorinated moieties in PFMAy-ec-PnAMAx-ec-PFMAy adsorbed at the solution/air interface were gradually completely replaced by PnAMA segments, resulting in an increase in corresponding solution surface tension until it was equal to that of poly(n-alkyl methacrylate) solution. Additionally, it was observed for the first time that the surface F/C ratios of spin-coated films decreased linearly with increasing surface tension of the corresponding film-formation polymer solution. Overall, the results indicate that the ultimate surface composition of spin-coated films of these fluorinated methacrylates was mainly dominated by their corresponding film-formation solution/air interfacial structure. This work provides a fundamental understanding of the formation of film surface structures from fluorinated polymer solution to the resulting solid film.