H/D Isotopic Exchange in Water Interactions with the Ferroelectric Copolymer:  Poly(vinylidene fluoride−trifluoroethylene) (70%:30%)

Abstract

For both water and heavy water adsorption and absorption on crystalline poly(vinylidene fluoride with trifluoroethylene (30%)), P(VDF-TrFE 70:30), two distinctly different adsorption sites have been identified by thermal desorption spectroscopy. One adsorbed water species resembles ice and there is also an absorbed water species that interacts more strongly with the polymer thin film, and in addition, there is a polymer surface (polymer to ice interface) water species. We find that there is H/D exchange between the water or heavy water molecules and the ferroelectric polymer (largely -(CH2-CF2)-), particularly at the polymer surface.

Energetics of the dipole flip-flop motion in a ferroelectric polymer chain

“…The calculated dipole moment per monomer ͑1.6 D͒ as well as structural parameters are all found to be in good agreement with other studies. 20,[31][32][33] All energy values reported in this paper are measured with respect to the total energy of the ideal structure.…”

Adsorbate/absorbate interactions with organic ferroelectric polymers

“…For thicker films, greater exposures to water are required for the formation of ice. This is evident from the thermal desorption spectra [21][22][23][24][25]27], and indicated in Figure 2b for P(VDFTrFE) samples roughly 35 Å thick. Because the desorption temperature of water from P(VDF-TrFE) above 280 K is associated with film thickness and water exposure, we associate this water species largely with absorbed water [22,23,25,27], but a surface species cannot be completely excluded [23,25,27].…”

“…The thermal desorption spectra of water from P(VDF-TrFE 70:30) are shown in Figure 2. Following exposure of water to crystalline thin films of P(VDF-TrFE 70:30) at 120-135 K, the thermal desorption spectra are largely characterized by two desorption peaks, and reported elsewhere [21][22][23][24][25]27]. Desorption of water at 150-160 K is characteristic of a water ice thin film sublimation (from the surface of P(VDF-TrFE 70:30).…”

“…From thermal desorption [21][22][23][24][25][26][27] and X-ray diffraction [19,20,22] studies, we find evidence that water is absorbed into the thin film bulk of the copolymers. The thermal desorption spectra of water from P(VDF-TrFE 70:30) are shown in Figure 2.…”

“…Again, water absorption does create distortions of the P(VDF-TrFE 70:30) chains leading to a reduction of crystallinity [19,20,22] and a distortion of the ferroelectric dipoles away from the surface normal in the immediate proximity to the water molecule [23]. This could also lower the activation barrier to dipole reversal (or just a significant dipole or multiple dipole reorientation) with electronic or dipole excitations.…”