Characterization of PVDF membranes by vibrational spectroscopy

In order to investigate the effectiveness of vibrational spectroscopy in the characterization of polymeric membranes, several poly(vinylidene fluoride) (PVDF) membranes with different porous structures were prepared by the phase inversion process using different casting solvents. An accurate analysis of the Fourier transform Raman (FT-Raman) and the Fourier transform infrared (FTIR) spectra was performed for each sample and the scanning electron microscopy (SEM) results were noted. To highlight the specific problems related to porosity and surface roughness in the acquisition of spectra by different sampling techniques, the attenuated total reflection (ATR) and photoacoustic spectroscopy (PAS) spectra were compared with corresponding spectra obtained from dense films. A detailed analysis of these spectra highlighted their ability in determining the differences in the polymer structure between the two membrane sides. This indicates that (considering the results given by all the different techniques) thorough qualitative membrane characterization can generally be achieved. Moreover, the good quality spectra of the PVDF membrane provide information on a portion of material which depends on its structure, highlighting the usefulness of FTIR-PAS in studying porous materials which, as a rule, give low quality infrared spectra when other sampling techniques are used. However, the complex and inhomogeneous structure of these materials can make quantitative analysis more, or less, difficult.