Abstract
Electrospinning is now commercially used for the fabrication of nano/micro fibers. Compared with spider dragline silk, artificial fibers have poor mechanical properties. Unlike natural silk, which has a hierarchical structure with an approximate 3-fold symmetry, the molecular structure of spun fiber has neither folding nor orientation. To date, it is almost impossible to control molecule orientation during the spinning process. Here, we show that macromolecule orientation can be easily controlled using the laminar flow of fluid mechanics. A lasting laminar flow in a long needle can order macromolecules. We find that the orientation of macromolecules can greatly affect the morphology and mechanical properties of fibers. We expect our technology to be helpful for more sophisticated fabrication of fibers with ordered macromolecules and DNA-like twists.
Highlights
Hierarchical structures in nature always behave extremely well, with astonishing functional properties that no manmade materials can match
Natural hierarchies always serve as a source of inspiration for scientists who hope to fabricate self-assembled macromolecular-scale nano/micro fibers embodying special functions, such as those of spider silk [9,10]
We will use laminar flow theory to control the molecular movement in the jet of the process, which might be used for the fabrication of the finest hierarchical layer in future; it would be possible to arrange macromolecules in a controllable way, like that of DNA structures
Summary
Hierarchical structures in nature always behave extremely well, with astonishing functional properties that no manmade materials can match. Electrospinning is widely used to prepare various materials for specific applications [14,15,16], and Richard-Lacroix and Pellerin have made important contributions to molecular orientation in electrospun fibers They showed the importance of controlling molecular orientation for some new and promising applications of molecule-oriented nanofibers [17] in mechanical engineering, thermal science, electrical devices, optical equipment, and puncture-proof fabrics [18,19,20,21,22]. The laminar flow indicates that when a spun solution goes through a needle, the flow velocity varies gradually from zero on the needle’s inner-surface to the maximum along the cross-sectional center of the needle [23,24,25] This velocity distribution is helpful to make macromolecules ordered. X-ray diffraction (XRD), scanning electron microscopy (SEM), a mechanical property testing machine, and transmission electron microscopy (TEM) are used to reveal that the molecular movement can be effectively controlled by the needle’s length; a longer needle organizes macromolecules in a better order
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