Microphase separation in PVDF/CoFe$_2$O$_4$ composite during FDM printing

This study is devoted to the investigation of 3D printing using functional polymer composites based on polyvinylidene fluoride (PVDF) with the addition of CoFe$_2$O$_4$ (CFO) nanoparticles at concentrations of 5, 10, and 15 wt.%. The microphase separation of the composite during filament formation and its subsequent effects on fused deposition modeling (FDM) printing and the properties of printed objects were studied. It was found that as the percentage of nanoparticles in the filament increased, the sizes of pores and pits on the periphery of the filament also increased. The appearance of defects in the polymer matrix at a CFO concentration of 15 wt.% was confirmed by differential scanning calorimetry (DSC), where an additional peak appeared on the enthalpy change curves. Although the highest content of the electroactive phase and the highest magnetization value were observed in the film printed from the filament with 15 wt.% CFO nanoparticles, the maximum magnetoelectric coefficient ($a_{33}$ = 3.2 mV/(cm$\cdot$Oe)) was achieved in the film printed with 10 wt.% CFO. This result is attributed to microphase separation. While the obtained magnetoelectric coefficient is lower than that of layered composites, it is sufficient for biomedical applications, such as regenerative medicine. Furthermore, the use of FDM printing technology enables the creation of complex structures, such as cell scaffolds.