Making porous membranes by chemical etching of

MARIANO GRASSELLI; BETZ, N.

NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH B - BEAM INTERACTIONS WITH MATERIALS AND ATOMS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2005 vol. 236 p. 501 - 507

0168-583X

PVDF (poly(vinylidene difluoride)) is one of the most resistant polymers commercially available. Its bi-axial phase has additional interesting technological properties such as piezo- and pyroelectric properties. Production of track etched membranes using heavy ion bombardment and subsequent chemical etching of PVDF films has been reported several years ago . However, a renewal interest in making porous membranes with pore diameter in the nanometer scale, encourages us to deep further in the etching mechanism and optimization of the chemical conditions to achieve membranes with lower pore diameters. In this work PVDF foils irradiated with Sn ions (2.85 MeV/uma) were exposed to several etching conditions, which involved permanganate oxidation in different alkaline environments (KOH >9 mol . L). The solution of KOH 9 mol . Land saturated in KMnO4 was the best to etch PVDF foils. Functional groups created in the alkaline and oxidative attack by permangante were studied by FT-IR and UV-vis spectroscopies. The spectroscopic data revel alkaline media produce mainly double bonds by a mechanism of dehydrofluorination and permanganate solution produce the oxidation these double bonds to carboxylic acid. In spite of the two very well delimited processes the tracks are only etched when both reagents are present at the same time, showing a synergistic mechanism. Etching time (1 to 15 h) and temperature (85 were the parameters that have the highest influence on the etching process. Etching temperature of 40 °C">40 was unable to produce pores independently of alkaline concentration of the solution and etching time. Pore diameter and shape were studied by electron microscopy.