The Zeta Potential of Track-Etched PVDF Membranes
The zeta potential gives comprehensive information about the charging behaviour of inner and outer membrane surfaces.
Irradiation of poly(vinylidene fluoride) films (PVDF) followed by chemical etching yields nanoporous membranes with tightly controlled pore sizes. These are used for highly specific filtration tasks like capturing blood cells or particles of known size.
The surface charge of a PVDF membranes with 50 nm pore size was characterized both on the outer surface (tangential mode) as well as inside the pores (transmembrane mode). In tangential mode the electrolyte is streaming along the membrane surface, whereas in transmembrane measurement the electrolyte passes through the membrane pores.The zeta potential inside the pores and on the outer surface is compared with the zeta potential of the untreated non-porous PVDF film.
Irradiation and especially oxidative etching introduce acidic functional groups into the inert PVDF surface. These functionalities shift the IEP from pH 4 (indicative for a clean polymer surface) to pH 3.2 independent of the measurement across the surface or through the pores. The difference in magnitude of the negative zeta potential reveals that the surface inside the pores is more affected (becomes more hydrophilic) by the treatment process.
O. Cuscito, M.-C. Clochard, S. Esnouf, et al, Nucl. Instr. and Meth. in Phys. Res. B 265 (2007) 309-313