RHEOOPTICAL FT-RAMAN STUDY OF UNIAXIALLY STRETCHED POLY(VINYLIDENE FLUORIDE)

A Fourier-transform Raman-spectroscopy-based rheo-optical system was u sed to study the process of uniaxial stretching of poly(vinylidene flu oride) (PVF2). This rheo-optical system made possible to reduce the ra te of stretching and favoured the acquisition of a higher number of sp ectra in different mechanical stages during the stretching process. Th ose can be the eleastic zone or the formation of the neck. Thus, it ha s been possible to establish that the stretching-induced phase transit ion in PVF2 takes place in the beginning of the neck formation. Shortl y after the neck development that transition has reached its maximum e xtent. The performance of the transition was highly temperature depend ent. As the temperature of stretching increases, the extent of the tra nsition decreases. Along with this permanent modification of the sampl e structure, other transient modifications were found. High resolution spectra of the phase beta of loaded PVF2 showed a wavenumber shift of specific absorption bands. These band shifts have been interpreted as a deformation of the geometry of the bonds reflected by the absorptio n band. Thus, bands with high contribution of skeletal CC bonds suffer ed the highest band shift, suggesting that these bonds were most sensi ble to the applied load. This band shift and, consequently, bond defor mation immediately vanished after removal of the load.