Synthesis and modification of cylindrical and conical nanopores on track-etched membranes

SILVIA SOTO ESPINOSA; MARIANO GRASSELLI

Salta

Congreso; VIII Congreso Iberoamericano en Ciencia y Tecnología de membranas; 2012

Universidad Nacional de Salta. CITEM 2012

Nanotechnology is growning faster than other technology in the last decade. In particular, the swift-heavy ions bombardment as a well-established technique to produce micro and nanopores onto polymeric films. An important feature of this approach is the ability to control properties such as the size and shape of these nanostructures. The present work is involving different physical and chemical conditions to produce nanopore membranes of different characteristics. The main goal is found a simple methodology to make nanopore membranes of different pore diameter, pore shape and chemical pore properties. Nuclear-track poly(ethyleneterephthalate) (PET) foils were irradiated with 84Kr of 250 MeV or 129Xe of 125 MeV/ ions with a fluence ions of 3.107cm2 and 7.107 cm2 respectively. Nanopore membrane with different pore diameter and pore shape were performed by changing experimental variables during the etching process, such as etching time, bath temperature, concentration of NaOH and UV light pre-treatment. Nanopores were visualised using a Field Emission Scanning Electron Microscopy (FESEM). Nanopore diameter reached by etching is directly proportional to the increase of etching temperature in the range of 30 °C to 60 °C, reaching pore diameters in the range of 40+/-8 to 540+/-100 nm at 2M NaOH and 25 min. The etching time was studied in the range between 10 and 66 min reaching pore diameters between 45+/-14 to 496+/-68 nm at 2M NaOH and 50 °C. Concentration NaOH was adjusted between 0.25 and 5M at 25 min and 50 °C. Pore diameter changed in the range of 60+/-14 to 420+/-34 nm. Additionally pre-irradiation with UV light was performed to increment the etching rate in the damage region [1]. Pre-irradiation (wavelength 320 nm) was applied for one hour each side of the foil reaching pore diameters in the order of 25+/-7 to 625+/-37 nm (Fig.1). Considering the combination of the four etching variables, we reached membranes with pores of pseudo-conical shape by UV pre-irradiation of only one side of the track-foils, and setting constant the other three etching variables (Fig.2). In a further step, residual radicals inside the track-etched membranes were used for internal pore wall modification by grafting on submicroscopic wall track method [2]. Briefly, immediately after etching, membranes were grafted by soaking in a methacrylate monomer solution of GMA (glycidyl methacrylate) under nitrogen atmosphere at 62 ºC. To visualise the grafting yield we used two methods, FESEM and fluorescent derivatization. Epoxy groups from polyGMA grafted at nanopore wall were modified with fluorescein. Finally labelled membranes were measured directly by Nanodrop® 3300 (fluorometer). Fluorescent relative units (RFU) increase in grafted membranes respect to the etched ones. This result was also confirmed by fluorescence microscopy. We also found a direct correlation between RFU and pore diameter reached at different etching temperatures (Fig.3). VER ADJUNTO