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.
Control of reflective cracking
The first is 'fatigue' cracking of the layer. This type of cracking is the result of the application of loads on the pavement and is controlled by appropriate thickness design which 'ill not be discussed in detail here. Thickness design includes not only the design strength and thickness of the stabilised, but other design elements such as delaying reflection cracking, or limiting stresses in the stabilised layer, by adopting a minimum thickness of overlying material. This may include an unbound layer utilising the 'upside down' pavement approach. The actual thickness required of the overlying material varies but for example PIARC (Ref.1) recently reported when the thickness of coated materials exceeds 20 cm the emergence of shrinkage cracks at the surface is generally uncommon; when it is 15 cm thick, the cracks emerge at the surface, but do not shorten the life of the surface course, especially if they are sealed. This experience has been gained 'with legal axle loads of 130 kN, considerably greater than the Australian legal axle load.