Vapor-Deposited Fluorinated Glycidyl Copolymer Thin Films with Low Surface Energy and Improved Mechanical Properties

Copolymer films of glycidyl methacrylate (GMA) with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA) and with (perfluoroalkyl)ethyl methacrylate (PFEMA) were synthesized using initiated chemical vapor deposition (iCVD). By varying the inlet monomer feed ratios during iCVD process, the mole percentage of fluorinated acrylics in the P(GMA- co -DFHA) and P(GMA- co -PFEMA) copolymers was systematically varied between 19% and 65%. Vacuum annealing of the as-deposited copolymer films induced cross linking between epoxy functionalities of the GMA units. Both the hardness and the modulus of the annealed copolymers films were observed to increase with increasing GMA fraction, providing an order of magnitude improvement in these mechanical properties. The dispersive surface energy of the annealed copolymers showed a limited dependence on GMA fraction, with the range of values being 17.5−18.6 mN/m and 9.9−14.7 mN/m for the P(GMA- co -DHFA) and P(GMA- co -PFEMA) films, respectively. These data are as low as or lower than the benchmark value for poly(tetrafluoroethylene). The low surface energies and the limited dependence on composition suggest an enrichment of fluorinated units at the surface, a hypothesis which was directly verified using angle-resolved X-ray photoelectron spectroscopy. The annealed iCVD fluorinated copolymers also demonstrate optical transmission of greater than 99% in the visible spectrum for films with a thickness of 700 nm. The resulting combination of enhanced mechanical properties, low surface energy, and optical clarity is desirable for many applications.