Abstract
Tailoring the secondary surface morphology of electro-spun nanofibers has been highly desired, as such delicate structures equip nanofibers with distinct functions. Here, we report a simple strategy to directly reconstruct the surface of polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) nanofibers by water evaporation. The roughness and diameter of the nanofibers depend on the temperature during vacuum drying. Surface changes of the nanofibers from smooth to rough were observed at 55 °C, with a significant drop in nanofiber diameter. We attribute the formation of the secondary surface morphology to the intermolecular forces in the water vapor, including capillary and the compression forces, on the basis of the results from the Fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy. The strategy is universally effective for various electro-spun polymer nanofibers, thus opening up avenues toward more detailed and sophisticated structure design and implementation for nanofibers.
Highlights
It is well recognized that distinctive secondary morphologies or structures, as found in, e.g., core-shell nanofibers [7], hollow nanofibers [8], triaxial nanofibers [9], tree-like nanofibers [10], surface-roughened nanofibers, etc., can significantly enhance functionality and efficiency
It is challenging to achieve sufficiently high roughness on polyvinyl alcohol (PVA)-nanofiber surfaces in order to anchor cells, gas molecules, or cement-hydration products because of the rather low surface tension of PVA solutions, which usually forces the formation of very smooth nanofiber surfaces during electrospinning
We report secondary-morphology formation on PVA nanofibers, (PVP)
Summary
The applications of nanofibers in air and water filtration [1], for catalyzing substrates [2], in various sensors [3], as biomedical scaffolds [4,5] and drug carriers [6] are rapidly increasing, thanks to their much larger surface area. Surface-roughened or grooved nanofibers with an easy-to-prepare secondary morphology are receiving fast increasing attention, as they offer useful interactions with surrounding objects at a low cost. They are being implemented at a fast pace into highly cell-attachable scaffolds [11], optimized ethylene-glycol gas sensors [12], stronger bonded construction materials [13], etc. Several routes, such as chemical corrosion or selective dissolution, are feasible for obtaining rough or grooved nanofiber surfaces. It has been shown that parameters such as solution concentration, externally applied voltage, flow rate, collecting distance, etc., during electrospinning are not suitable for preparing PVA
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