Coaxial electrospinning process toward optimal nanoparticle dispersion in polymeric matrix

Nano-reinforced polymers have gained popularity in the last decades since they exhibit enhanced properties (compared to pristine polymers) that are useful in a wide range of applications. Unfortunately, dispersion of nanoparticles (NP) into polymeric matrices is a major problem since they tend to form agglomerates, limiting the improvement of properties and further applications. In this work, we propose the use of coaxial electrospinning as onestep method to disperse nanoparticles in a polymeric matrix. Particularly, iron oxide (Fe 3 O 4) NP with a monomodal and bimodal size distributions were dispersed in polyvinylidene fluoride (PVDF), a material that is well-known for its improved piezoelectric properties when it is processed via electrospinning. The results indicate that the incorporation of NP modified the polymeric fiber depending on their surface-to-volume ratio (smaller NP promoted smaller fiber size). Moreover, TEM revealed a good NP dispersion in the polymer, especially for the smallest NP size (monomodal). Finally, each NP size distributions were well preserved in the electrospun mats compared to the initial NP solutions, demonstrating the suitability of this technique for the fabrication of nano-reinforced PVDF structures with tailored NP size. Overall, this method could represent a facile and practical alternative to fabricate materials with piezoelectric/super-paramagnetic properties.