DNA increases the β-phase content of PVDF films

Deoxyribonucleic acid (DNA) has been shown to interact with poly(vinylidene fluoride) (PVDF), resulting in increased electroactive β-phase content and piezoelectric response under certain casting conditions. While the use of DNA as a self-poling agent has the potential to eliminate the need for additional stretching and poling steps in piezoelectric PVDF films, the mechanism through which DNA poles PVDF is not yet well understood, hindering the optimization of the process. Here, we performed a study to screen the effects of drying temperature, amount of nucleic acid additive, weight percentage of PVDF, spin-casting speed, and molecular weight of PVDF on spin-cast PVDF-DNA hybrid films. The phase composition and piezoelectric response of the resulting films were quantified using Fourier-transform infrared spectroscopy (FTIR) and a piezoelectric meter, respectively. We found that DNA has a significant influence on the PVDF films' β-phase content; however, this effect is masked at low drying temperatures. While DNA facilitates the formation of the electroactive β-phase of PVDF, we could not find evidence that DNA enhances PVDF's piezoelectric response. These results conflict with previous literature, which reported that DNA aligns the dipoles of PVDF such that the films exhibited a significant piezoelectric response. Overall, this study identifies that nucleic acid additives - under certain casting conditions - have an important effect on PVDF film phase composition.