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.
Temperature influence on the gas desorption from polyvinylidene fluoride (PVDF) irradiated with helium beams
Abstract Polyvinylidene fluoride (PVDF) is strongly modified by ion irradiation. PVDF films were bombarded with helium beams, 50-350 keV in energy and ion doses ranging between 1012 and 1015 ion/cm2. Irradiations were performed in vacuum at different temperatures from-150 up to +100°C. Ion irradiation of the fluropolymer produces H2 and HF gas desorption, which yields are proportional to the temperature, as detected ‘in situ’ by a quadrupole mass spectrometer. The results can be qualitatively explained by assuming that free radicals of hydrogen and fluorine, produced along the ion track, can diffuse throughout the sample, react, and the resulting melecules desorbed from the polymer surface. Residual irradiated polymer remains drastically modified and rich in carbon content.
Graphitic clusters in hydrogenated amorphous carbon induced by keV-ion irradiation
Energy gap and hydrogen concentration have been measured in hydrogenated amorphous carbon (a‐C:H) after bombardment with 100 keV He+ and 300 keV Ar+ ion beams, up to ion fluences 3×1016 ions/cm2. a‐C:H films have been obtained by ion irradiation at low ion fluences of polystyrene layers and with a subsequent low‐temperature annealing (400 °C, 10 min). Experimental values for the energy gap (2.5–0.5 eV) and hydrogen concentration (7.4×1022–1.8×1022 H atoms/cm3) have been interpreted in terms of a graphitic cluster structure with a different size (3–20 A). We were able to determine experimentally the value of the bond integral ‖β‖ and we found it in good agreement with the calculated one for graphite.