Do surface effects explain the unique elasticity of polymer nanofibers?

The elastic modulus of electrospun Polyamide (Nylon-6.6) nanofibers, which sharply increases in nanofibers with diameters below 500 nm, was measured by both bending and tensile deformation modes. Since the nanofiber surface energy contributes significantly to the elastic modulus measured by bending, but is negligible in the modulus obtained by stretching, the contribution of the surface energy to the modulus can be extrapolated from datasets collected after both types of deformation. The results unambiguously show that the abrupt increase in the elastic modulus of the nanofibers cannot be attributed either qualitatively or quantitatively, to a surface energy effect. The presented results contradict earlier claims with regards to the contribution of surface energy to the elastic modulus. In addition, these data suggest that the confinement of the supermolecular structures within nano-objects formed during nanofiber processing is responsible for the observed modification in elastic modulus. Copyright (C) EPLA, 2011