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.
KeV-MeV ion irradiation of polyvinylidene fluoride (PVDF) films
Abstract Semicrystalline polyvinylidene fluoride (PVDF) films have been irradited with different ion beams and energies ranging between 0.1 keV/amu and 6 MeV/amu. Polymer modifications induced by the ion irradiation, for electronic and nuclear energy stopping, have been investigated in situ by a highly sensitive quadrupole mass spectrometer. Ion irradiation of PVDF produced ejection of H 2 and HF molecules with a high chemical yield. Switching on the ion beam, the measured yields show a prompt (for H 2 ) and a slow (for HF) component of the molecular emission, which depends on the ion energy, ion fluence and polymer temperature. Along the ion track, the energy deposition produces a high density of active species, which give rise to desorbed molecules, to cross-linking processes and to a very stable residual carboneous film. At room temperature, the diffusion coefficient of HF molecules measured in irradiated PVDF is of the order of 10 −8 cm 2 /s. The structural modifications of the irradiated films have been investigated ex situ by X-ray diffraction and optical absorption. The ion energy deposition along the ion track can be useful to realize active bio-membranes through the polymer grafting process.
High energy ion beam modification of polymer films
Abstract Studies on the effects of high energy ion beam irradiation in polymer films are reviewed in this paper. The studies reported in this review suggest exciting research in the field of ion-polymer interaction with impact on electronic transport in disordered systems, dynamical radiation chemistry and novel materials synthesis. p ]High energy ions (> 10 keV amu ) deposit a large amount of energy (several eV atom ) in ionizing the electrons of the target atoms. This results in significant destruction of bonds in the films as a result of which polymers undergo rapid dissociation. Using a quadrupole mass spectrometer, the study of transient emission of molecular species produced by an ion pulse has been shown to yield information about the diffusion and reaction kinetics of various molecules in the polymer. The fact that polymers undergo dissociation and those atoms which form volatile species are selectively depleted from the film could be utilized in producing useful inorganic composites by ion bombardment of polymers. For example, hard SiC composite films have been produced by ion beam irradiation of organo-silicon polymers. Eventually, polymer dissociation leads to a predominantly carbon containing film which exhibits interesting electronic transport properties. Experiments on ion irradiated, pure carbon films indicate that a metallic form of carbon is produced from the polymer films at high irradiation doses. While experiments on disordered conductors have involved the ion beam modification of highly conducting materials to form bad metals (with resistivity, ρ ∼ 10 −3 −10 −4 Ω cm ), comparable bad metals are formed in these experiments starting with insulating materials. There have been, in addition, interesting studies on polymer films using low energy ions (in the ion implantation regime) as well and a brief review of these studies have also been included in this paper.