(5bs) Initiated Chemical Vapor Deposition of Thin Polymeric Coatings

Vapor deposition can be used to produce a wide variety of polymeric thin films. Vapor deposition has the environmental benefit of using no solvents and the process can be used to conformally coat substrates with complex geometries such as fabrics and wires since there are no surface tension problems. Initiated chemical vapor deposition (iCVD) is a low energy vapor deposition process (0.01 W/cm²) that can be used to produce linear polymers in which the pendant chemical moities are kept intact. iCVD has been used to polymerize many vinyl monomers such as glycidyl methacrylate, 2-hydroxyethyl methacrylate, and 2-(perfluoroalkyl)ethyl methacrylate. Deposition rates as high as 200 nm/min have been achieved using iCVD. The proposed polymerization mechanism is the classical free radical polymerization mechanism of vinyl monomers. Monomer and initiator gases are fed into a vacuum chamber where resistively heated wires are used to thermally decompose the initiator molecules into free radicals. The free radicals then attack the vinyl bonds of the monomer molecules. Propagation occurs on the surface of a cooled substrate.

In this study, the kinetics associated with the iCVD process will be examined and the iCVD process will be scaled up. The process will also be used to functionalize the surfaces of polymeric membranes. These membranes have monodisperse pore distributions and vary in porosity, length, and diameter. iCVD will be used to coat these membranes with a low surface energy (10 mN/m) fluoropolymer that renders the membranes both hydrophobic and oleophobic. Contact angle measurements have been used to show that the hydrophobicity of the coated membrane is much larger than the uncoated membrane and x-ray photoelectron spectroscopy has been used to verify the presence of fluorine in the coated membranes. Dynamic contact angle measurements show a low hysteresis indicating that the internal pore surfaces are coated with the fluoropolymer. We are currently studying the depth of penetration of the coating as a function of pore diameter, pore length, and coating thickness using an electron microprobe.