Chemical modification of polypropylene and polystyrene through fluorocarbon ion beam deposition

Classical molecular dynamics (MD) simulations are used to examine the deposition of polyatomic fluorocarbon (FC) beams on polypropylene (PP) and polystyrene (PS) surfaces. The goal is to investigate the ways in which different FC ions, in this case CF₃⁺ and C ₃⁺C₃F₅⁺, chemically modify the two different polymer surfaces. The simulations predict that the chemical reactions that occur upon impact are highly localized. As a result, with the same incident energy, CF₃⁺ ions generate more PP chain fragments and facilitate more etching of the surface than C ₃F₅⁺ ions. In contrast, C₃F ₅⁺ ions promote more cross-linking between PP chains and the growth of FC films on the PP surface. In PS, there is more penetration of the ions than in PP as well as increased formation of CF₂ particles, which indicates that deposition on PS yields fluorocarbon films more easily than deposition on PP. The simulations thus provide important insights into the complex mechanisms associated with the processes used to engineer polymer thin films in FC ion beams and plasmas and illustrate how differences in polymer structure ultimately influence such properties as sputtering, chemical modification, and thin film growth.