Ferroelectric phenanthrene nanofibers by electrospinning

Ferroelectric nanofibers, based on the insertion of ferroelectric compounds into a polymer matrix, have been attracting strong interest due to their potential for technological applications, namely in sensors/actuators where their dielectric, pyroelectric and piezoelectric characteristics can be exploited. In this respect, nanofibers prepared by the versatile electrospinning technique present a high surface to- volume ratio and unique structure, allowing to tailor the fiber diameter down to the nanometer scale. Phenanthrene is an organic ferroelectric material that has been studied mainly in its bulk form and it has not been explored for the incorporation in functionalized nanostructures. As such, in this work we have studied the synthesis of phenanthrene nanofibers by electrospinning and their structural, dielectric and pyroelectric properties were characterized. The X-ray diffraction and Raman studies show that the prepared fibers are polycrystalline presenting the monoclinic ferroelectric structure. Scanning electron microscopy (SEM) measurements show that the fiber diameters are in the range 198-305 nm, being composed by phenanthrene inclusions embedded inside the polymer matrix. The temperature dependent permittivity studies indicate that the ferroelectric transition temperature (Tc) is ~ 75 ºC, similar to its bulk value (Tc,bulk = 72 ºC), with some hysteresis under temperature cycling. Pyroelectric measurements allowed to determine the pyroelectric coefficient, which similar to the bulk value. The observed behaviors were correlated with the nanosized character of the polar ferroelectric inclusions inside the synthesized nanofibers.