A convenient method was developed to fabricated helical nano-fiber yar n in one step and with high efficiency.Poly(vinyl pyrrolidone) (PVP) sol (Mw =1.3×106，10% in ethanol) was electrospun at the voltage of 25 kV

using a t hin upright copper needle as a collector with the rotation speed of 0～1200 r/min.In t hi s setup

centimeters-long precursor fibers are spontaneously electrospun on the tip of the upright needle target parallel to the electric field.The electrospin ning process is mainly controlled by the electrostatic forces.Thus

when a grou nded needle is close to the splaying jet

the splaying jet will be converged and then deposed on the needle.The yarn was formed between the needle and the spin neret

and the jet will be folded and aligned to form a self-bundling yarn.The morphologies of helical fiber were observed by scanning electron microscopy (SEM ).The morphologies of PVP fibers were changed from non-helical

dispersed-helic al to tight-helical fibers forming a multi-filament yarn in the various ro t ating speeds.The Coulomb attracting force (in the vertical direction due to the static fields between the jet and the copper thread)

the Coulomb excluding forc e between the spinning fibers (in the horizontal direction) and the shear force (in the tangential direction due to the high rotation speed by copper needle) ar e the three main factors to form the helical fibers.The main advantages of prod ucing PVP fiber yarns by this technique are the minimum polymer degradation and forming the multi-filament yarns having a high tenacity.