Radiation tolerance in polymeric dielectrics by small molecule doping, Part II: Thermodynamic and kinetic parameters

The doping of Mylar® film (composed of semicrystalline poly(ethylene terephthalate)) with small molecule electron traps results in a high-quality dielectric film with excellent radiation tolerance. Fluorenones with electron-withdrawing substituents, doped from ethylene glycol, are excellent candidates to provide this radiation tolerance. Utilizing theories for diffusion and partitioning, this paper extracts kinetic and thermodynamic information from the doping process. Diffusion is significantly retarded, and partitioning significantly enhanced, upon the addition of polar substituents to the dopant molecule; dopant size has a minor impact. Diffusivity corrections due to tortuous paths around the crystallites are accounted for. Additionally, it was found that the solubility parameters, in combination with estimations for the local interaction volumes, provide an excellent method to predict trends in the equilibrium doping behavior via the χ parameter and hydrogen bonding-modified Flory-Huggins theory. Based on this method, estimations are given for the number of hydrogen bonds between ethylene glycol and dopant molecules.