Dielectric properties at microwave frequencies of poly(ɛ-caprolactone)/CNF films and electrospun mats

The electromagnetic (EM) properties of hybrid poly(epsilon-caprolactone)/carbon nanofiber films and electrospun mats at microwave frequencies (8.2-12.4 GHz) were assessed by means of wave guide measurements. It was found that, on equal composition, the two systems present very different permittivities, that in the case of electrospun mats is far lower than that of films. These results are explained in view of the different microstructures. In particular, the massive presence of porosity is demonstrated to be the major parameter affecting the EM properties of mats. Shielding effectiveness was evaluated and was found to be poor for both systems, despite the relative large amount of conductive nanofiller. This results was attributed, in the case of films, to the presence of multiple reflections among CNF, while in the case of mats to their porous microstructure that let the waves easily pass through. (C) 2011 Elsevier B.V. All rights reserved.