Imaging the Effects of Annealing on the Polymorphic Phases of Poly(vinylidene fluoride)

Abstract

The effect of annealing on the phase transformation and the dielectric properties of poly(vinylidene fluoride) (PVDF) is explored using quasi-single molecule (quasi-SM) microscopy. The solvatochromic properties of nile red (NR) are employed to measure the spatial distribution of the local dielectric constant (ε) in ∼30 μm thick PVDF films before and after annealing at 90 °C. The results presented here demonstrate that nonannealed films exhibit much larger ε distributions, both in terms of magnitude and distribution, when compared to annealed films. The polymorphic phase of PVDF before and after annealing is also confirmed using X-ray diffraction. Nonannealed films are found to be in the γ-phase with annealing promoting the transition to primarily β-phase. Combining these results, we conclude that the decrease in ε with annealing time is due to the phase transformation from γ- to β-phase. Using quasi-SM imaging techniques one can readily visualize the ε environments present within different polymorphic phases of PVDF.

Multiscale-structuring of polyvinylidene fluoride for energy harvesting: the impact of molecular-, micro- and macro-structure

“…It has also been shown that annealing of the PVDF thin lms at 90 C transforms the g-phase to the b-phase and this is re-ected in a decrease of the relative permittivity. 77 Recently, nanofabrication technologies such as electrospinning, nanoimprint lithography 78 and the horizontal Langmuir-Schaefer technique 79 have attracted attention to produce non-volatile memory and exible piezoelectric sensors. In particular, electrospinning can produce a high b-phase content in PVDF nanobers via a one-step process that avoids additional processing stages such as mechanical stretching or electrical poling; this process will be described later in Section 2.2.8.…”

Optical Microscopic Techniques for Synthetic Polymer Characterization

“…Early experiments in which single molecule spectra were obtained using a sample scanning confocal microscope demonstrated the utility of this method for characterizing local environments in polymer films . Quasi-single molecule imaging methods have since been used by Hess et al to obtain the fluorescence emission wavelength of Nile Red doped into 30 μm-thick PVDF films . These data allowed them to visualize spatial variations in the local dielectric constant of the polymorphic polymer films.…”

“…38 Quasi-single molecule imaging methods have since been used by Hess et al to obtain the fluorescence emission wavelength of Nile Red doped into 30 μm-thick PVDF films. 39 These data allowed them to visualize spatial variations in the local dielectric constant of the polymorphic polymer films.…”

Enhancement Research on Piezoelectric Performance of Electrospun PVDF Fiber Membranes with Inorganic Reinforced Materials

“…However, what can be obtained by the traditional preparation process of PVDF membranes is the nonpolar α-phase [12]. The β-phase of obtained PVDF membranes should always be induced by some post-processing treatments, such as mechanical stretching, annealing, and high voltage poling [13][14][15][16]. Compared with the complex traditional preparation process of PVDF piezoelectric membranes, the electrospinning process, including the ejection of the PVDF solution, volatilization of the solvent, stretching of the electrospinning streams, and high voltage polarization, could be completed in one step and the β-phase content of the prepared PVDF membranes were improved with the function of high voltage and stretching, which exhibit the better piezoelectric properties [17].…”