Mechanical deformation and failure of electrospun polyacrylonitrile nanofibers as a function of strain rate

The mechanical deformation of 12 mu m long electrospun polyacrylonitrile (PAN) nanofibers with diameters of 300-600 nm was investigated. The nanofibers were subjected to cold drawing in atmospheric conditions and at strain rates between 10(-2) and 10(-4) s(-1). The ultimate strain of the PAN nanofibers was 60%-130% varying monotonically with the strain rate. On the contrary, the fiber tensile strength, ranging between 30 and 130 MPa, varied nonmonotonically with the slowest drawing rate resulting in the largest ductilities and fiber strengths. At the two faster rates, the large fiber ductilities originated in the formation of a cascade of ripples (necks), while at the slowest strain rate, the nanofibers deformed homogeneously allowing for the largest engineering strengths and extension ratios.