Dry degradation processes at solid surfaces

Abstract

Polymer surfaces were modified by exposure to a silent discharge plasma, by exposure to UV radiation and by chemical functionalisation. Additionally, the silent discharge treatment of alkali halide disks was investigated. Employing XPS and IR, the silent discharge treatment of poly (phenylmethylsilane) and poly (cyclohexylmethylsilane) thin films was found to result in the formation of a carbonaceous SiO(_x) layer. Oxidation occurred faster and to a larger degree in the case of the aromatic polysilane. A XPS study of the UV irradiation of poly (phenyhnethylsilane) thin films in the presence of CCI(_4) vapour revealed the formation of a chlorinated silicon species. The analysis of aged samples showed that this initially formed product was unstable in moist air. The silent discharge treatment of alkali halide disks (KCI, KBr, KI) was studied in ambient air, as well as in dried and humidified gases (artificial air. He, N(_2), O(_2)). IR and XPS were used as analytical methods, hi most cases nitrate and halogenate were formed upon treatment in air. Depending on the reaction conditions treated KI disks sometimes showed the presence of nitrite as an additional or as the main product. In oxygen atmospheres halogenate was formed as the exclusive product. Treatments in the remaining atmospheres did not lead to product formation. The presence of water vapour in the feed gas increased the amount of product. Changes in the IR spectra of the nitrate species upon storage in a desiccator and after exposure to heat were found and monitored. Pentafluoropropionic anhydride was tested for its suitability as a vapour phase labelling reagent for hydroxyl groups on polymer surfaces. Derivatised films were analysed by XPS and IR. Using Polyvinyl alcohol as a model polymer the reaction proceeded fast and quantitative. Moreover, the cross-reaction with a number of polymers containing functionalities other than hydroxyl was studied. The reaction with nylon 6,6 was investigated m detail. The vacuum photodegradation of polyethersulfone upon irradiation with the full and a selected part of a Hg (Xe) lamp spectrum was studied. The volatile products were identified with in-situ quadrupole mass spectrometry. Monitoring the intensities of some products in subsequent irradiation phases provided evidence for a crosslinking process. In samples irradiated with the complete lamp spectrum crosslinkmg occurred faster. Additionally, the XP spectra of the corresponding samples revealed a stronger modification which became most obvious in the presence of a reduced sulfur species.