Nanoporous modification by simultaneous gamma radiation grafting

MARIA LAURA CARBAJAL; GERARD PEPY; MARIANO GRASSELLI

Angra dos Reis

Simposio; 8th International Symposium on Ionizing Radiation and Polymers (IRaP); 2008

Production of track-etched membranes using heavy ion bombardment and subsequent chemical etching of polymeric films has been reported several years ago. However, there is a renewal interest to make track-etched membranes with pore diameter in the nanometer scale containing specific chemistry onto its surfaces. Track membranes with pore diameters at molecular dimensions have direct application in molecule and ion sensing through resistive-pulse sensor method. Another interesting application can be come from the introduction of chemical selectivity in order to confer a molecular recognition in the selective-permeation function. Specific chemical interactions between solute and the modified nanopore walls can alter the transport properties. Most of the advances in this field have been done on commercial track-etched membranes modified with a gold deposition by electroless plating method to reduce the pore diameter. This work is focused in the modification of track-etched polyethylene terephthalate (PET) membranes by simultaneous radiation induced graft polymerization in order to modify the internal surface of porous material at the nanometer dimension. PET foils were irradiated with a heavy ion beam of Kr and Xe (10 MeV/uma, ion fluence 3 x 109/cm2) in vacuo provided by GANIL laboratory. Small pieces of irradiated PET were etched with NaOH solution 0.25 N 80°C during 45 min. In a second step, glycidyl methacrylate (GMA) solutions, at very low concentrations (between 0.1 % and 0.6 % v/v), were used as monomer to induced simultaneous grafting on track-etched PET membranes using 60Co gamma source at 6 kGy. Different monomer concentration reaches proportional grafted polymer (degree of grafting between 1 and 6 %) which was further chemically modified by ring-opening reaction onto the epoxy groups. The chemical reaction of iminodiacetic acid was carried out in the last step. Small Angle Neutron Scattering (SANS) were performed to analyze pore diameter and homogeneity of the grafted nanoporous. The quality of the samples and the experiment was proved by the observation of the oscillations of the Bessel function, characteristic of the scattering function of a straight cylinder. Fitting the dispersion pattern to a mathematical model, reaches a reduction in the pore radius in the order of 3 to 5.6 nm in the grafted samples. Track-etched pore diameter was initially 67.4 nm. All chemical steps were following by FT-IR ATR spectroscopy.