Microfilters for biomedicine obtained by swift ion processing.
Swift ions with 50 MeV energy are used to irradiate bio-polymeric films. Lithium, carbon and oxygen beams, with fluencies ranging between 10(8) and 10(13) ions/cm2, are swept on large surfaces of hydrogenated and fluorated polymers. The electronic stopping power of the ion induces high rates of ionization, excitation and radical formation along the ion path with production of chain-scission and cross-linking processes which can be investigated by the molecular emission from the irradiated polymer. The radiation damage increases the chemical solubility of the material around the ion track up to distances of the order of 100 nm. A suitable chemical etching removes the damaged material leaving micrometric holes in the polymeric film. This process gives rise to micro-perforated films which can be used as microfilters, with sub-micrometric pore dimension, high selectivity and controllable porosity. Their use is very interesting for special applications in ultra- and microfiltration of biological liquids.
Structural modification of polymer films by ion irradiation
Abstract The atomic and electronic structure of polymer films undergoes deep modifications during high energy (keV-MeV) ion irradiation, from molecular solid to amorphous material. At low energy density (1022–1024 eV cm 3 ) typical effects include chain scissions, crosslinks, molecular emission and double bonds formation. In hydrocarbon polymer (polystyrene, polyethylene) the main effect of irradiation is the formation of new bonds as detected by molecular weight distribution, solubility and optical measurements. Moreover the concentration of trigonal carbon (sp2) in the polymer changes with ion fluence (1011–1014 ions cm 2 ) and stabilizes to a value of 20% independently on the initial chemical structure of the irradiated sample. Photoemission spectroscopy shows an evolution of valence band states from localized to extended states. At high energy density (1024–1026 eV cm 3 ) the irradiated polymer continues to evolve showing spectroscopic characteristics close to those of hydrogenated amorphous carbon. Trigonal carbon concentration changes with ion fluence (1014–1016 ions cm 2 ) reaching the steady state value of 60% and the hydrogen concentration decreases to 20%. Moreover the values of the optical gap (2.5–0.5 eV) suggest the presence of medium range order in the obtained hydrogenated amorphous carbon. These values are consistent with the formation of graphitic clusters, whose size goes from 5 A to 20 A by changing the ion fluence (or energy density).
Calorimetric measurements of MeV ion irradiated polyvinylidene fluoride
Abstract High energy ion irradiation of semicrystalline polyvinylidene fluoride (PVDF) films changes its melting behaviour. After irradiation with 9 MeV carbon beam, differential scanning calorimetry of PVDF flims exhibits a quite complex behavior in the temperature range 20–200°C. At low ion fluence irradiation (