Enhanced Electroactive Phase Content of PVDF Composite Thin Film by Tuning DyFeO₃ Nanoparticles

The design and development of Poly(vinylidene fluoride) (PVDF) based composites became the hotspot of the material science in recent years due to its promising applications in sensors, wearable portable self-powered systems, actuators. The application potentiality of PVDF can be tailored by improving the electroactive phase content, which can be achieved effectively by adding nanofillers into the pure PVDF. The incorporation of nanofillers not only improves the electroactive phase content, it also useful to enhance piezoelectric, dielectric, electrical conductivity and energy density of PVDF. Herein, we have studied the influence of DyFeO₃ (DFO) nanoparticles to improvising the electroactive phase content of the PVDF matrix. The DFO nanoparticles as a filler embedded to PVDF polymer matrix with different concentration (3, 6, 9, 12 and 15 % respectively) were fabricated using the doctor blade set up. For the formation of films, initially the granular Polyvinylidene Fluoride was added in Dimethylformamide (DMF) solvent and stirred at 70 ^oC for 1-2 h to completely dissolve. We added the filler in a clear PVDF and DMF solution as per the weight percentage and stirred for 24 hr for homogeneous blending of the nanoparticle and PVDF composite. The solution was ultrasonicated for 1 hr prior to the film preparation. The ultrasonicated solution were cast on doctor blade equipment to get a uniform film of DFO-PVDF (DFP). To know about the structural property of DFP composites, the room temperature XRD of DFP films was performed at 5 to 80^o diffraction angle range. The crystalline peaks of DFO filler and PVDF peaks completely matched with all DFP composites and it suggests that both (DFO and PVDF) characteristic present in DFP composite films. The peak position at 19.8^o and 20.4^o diffraction angle corresponding to nonpolar α and polar β-phase and planes associated with these two peaks are (020) and (110)/(200). The electroactive phase analysis was investigated from FTIR measurement. Electroactive phase content calculated with the help of Beer-Lamberts law by considering the 766 and 840 cm^-1 band corresponding to nonpolar α and electroactive phase (both β and γ phase). The obtained values are 72.86, 77.51, 79.27, 82.36, 83.42 and 83.50 for PVDF, 3, 6, 9, 12 and 15 wt%, respectively. To know about the individual contribution of β and γ phase in electroactive phase we deconvoluted peaks in the range 800 to 860 cm^-1. The peak centered at lower wavenumber around 828 cm^-1indicates γ phase and the peak at higher wavenumber at 838 cm^-1corresponds to the β phase. For all the composites including neat PVDF, the β phase found to be the dominant phase than the other phase. To again confirm the existence of β phase, we carried out the DSC measurement as the γ phase melting temperature is relatively higher than the β phase. From the DSC it is observed the melting peak appeared at ~172 ^oC,which agrees well with the melting temperature of β phase. So, the prominent peak at 20.4^oin XRD, individual phase content analysis through Beer-lambert law from FTIR and DSC melting peak investigation confirmed the improved β phase content in the polymer nanocomposites.