Vibrational Sum Frequency Generation (SFG) Analysis of Ferroelectric Response of PVDF-Based Copolymer and Terpolymer

In poly(vinylidene difluoride) (PVDF)-based polymers, the alignment of dipoles of the crystalline beta phase with all trans conformations is responsible for ferroelectricity; however, there is a lack of direct spectroscopic evidence for this phenomenon. We report in situ monitoring of the molecular orientations associated with ferroelectric responses of PVDF-based polymers using vibrational sum frequency generation (SFG) spectroscopy. The orientation of CH2 groups with respect to the -(CH2CF2)(n)- chain axis of the poled beta domains in a PVDF copolymer was determined from the SFG dependence of an uniaxially aligned sample on the laser polarization and azimuthal angle. The relative intensities of CH2 symmetric and asymmetric stretch modes as well as their total intensities revealed the transformation of the all-trans conformation domains during the electrical poling of PVDF based co- and terpolymer films.