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 ion beam irradiation of polyvinylidene fluoride (PVDF)
Abstract Polyvinylidene fluoride (PVDF) films were bombarded with 50–350 keV ion beams with fluences of about 1 × 1015 ions/cm2. Structural modifications induced by the ion beam irradiation were studied ‘in situ’ by monitoring the desorbed gases from the irradiated polymer by quadrupole mass spectrometry and ‘ex situ’ by X-ray diffractometry analysis. The chemical yields of the emitted H2 and HF molecules are of the order of 1 desorbed molecule per 100 eV incident energy. The chemical yields of these molecules were investigated as a function of the irradiation conditions and ion fluences. The experimental results are discussed from the standpoint of the chemical evolution induced by ion energy deposition in the bio-polymer.
General expression for the density effect for the ionization loss of charged particles
The equations for the density-effect correction $\ensuremath{\delta}(X)$ for the ionization loss as given in a previous paper have been extended to the case where $\ensuremath{\delta}({X}_{0})\ensuremath{\equiv}{\ensuremath{\delta}}_{0}g0$. Here ${X}_{0}$ is the lower limit of the range ${X}_{0}lXl{X}_{1}$, where a particularly simple expression for $\ensuremath{\delta}(X)$ applies; $X={log}_{10}(\frac{p}{{m}_{0}c})$, where $p$ is the momentum and ${m}_{0}$ is the mass of the incident particle. The case ${\ensuremath{\delta}}_{0}g0$ applies directly to the calculation of $\ensuremath{\delta}(X)$ for conductors (metals).