3. Results and discussion
The morphology of the electrospun PVP and PVP/Eu-PEG compo- site fibers with different PEG molecular weights are shown in Fig. 1. The elementary compositions of PVP/Eu-PEG nano fibers are further confirmed by a energy dispersive X-ray spectrometer (EDX), as reveals in Fig. 2. Both the neat PVP and the PVP/Eu-PEG fibers were quite uniform in diameter and cylindrical with smooth surfaces, which indicate that PVP and Eu-PEG are miscible and compatible in the composite fibers. From SEM observations (Fig. 1), we saw that the average diameters of the electrospun PVP/Eu-PEG composite fibers increased from 796 to 1190 nm with increasing PEG molecular weight, which is nearly two to three times larger than that of the PVP fibers ( 350 nm).This result