Polyimide Films from Vapor Deposition: Toward High Strength, NIF Capsules

The focus of recent efforts at LLNL has been to demonstrate that vapor deposition processing is a suitable technique to form polyimide films with sufficient strength for current National Ignition Facility target specifications. Production of polyimide films with controlled stoichiometry was accomplished by: 1) depositing a novel co-functional monomer and 2) matching the vapor pressure of each monomer in PMDA/ODA co-depositions. The sublimation and deposition rate for the monomers was determined over a range of temperatures. Polyimide films with thicknesses up to 30 μm were fabricated. Composition, structure and strength were assessed using FTIR, SEM and biaxial burst testing. The best films had a tensile strength of approximately 100 MPa. A qualitative relationship between the stoichiometry and tensile strength of the film was demonstrated. Thin films (∼3.5 μm) were typically smooth with an rms of 1.5 nm.