Surface and in-depth molecular characterization of plasma-treated polymers and plasma-polymers using SIMS

The use of plasma technologies under atmospheric pressure for the surface modification of polymers and the deposition of thin polymer films has expanded enormously since the last decade, finding countless applications in several sectors, such as material science and medicine. De facto, these plasma-related polymers are systems extremely complex to characterize. Thanks to the latest advent of large noble gas clusters for ‘damageless’ sputtering of organics, time-of-flight secondary ion mass spectrometry (ToF-SIMS), a well-known surface-sensitive technique, is now able to probe the detailed chemical structure of any organic material along the third dimension. In this thesis, new ToF-SIMS methodologies for the surface and in-depth chemical characterization of plasma-treated and plasma-synthesized polymers under atmospheric pressure were developed. To this purpose, two challenging case studies were defined: 1) Polyethylene films exposed to an Ar-H2O post-discharge of an atmospheric plasma torch. Owing to the high isotope sensitivity of SIMS, the H2O reactivity with the polymer films was successfully traced as a function of the parameters “treatment time” and “sample-torch distance”. For the first time, the surface chemical characterization could be correlated with the in-depth modifications; and 2) Polystyrene-like films synthesized near atmospheric pressure by a dielectric barrier discharge. The chemical structure of the deposited coatings was investigated as a function of the plasma power, after exposure to the ambient air but in the inner layers. This expedient permits to perform ex-situ characterization, even in presence of post-polymerization oxidation.