Control And Self-Assembly Of Fiber-based Nanostructural Materials

Since the first patent on electrospinning has been applied by Formhals, Electrospinning, as a simple and effective method for organic/inorganic nanofibers, has gained special attention. Additionally, electrospun nanofiber can act as a bridge between the nanoscale and macroscale for their nanoscale diameters and macroscale lengths. In recent years, with the development of electrospinning, the preparation of hybrids nanofibers for their multi-functional properties has been of current interest. However, how to fabricate nanomaterials with controlled-morphologies and controlled-position based on electrospun nanofiber and self-assemble them into controlled structures are still big challenges.My thesis involves two parts based on electrospinning technique: (1) Preparation of morphologies-controlled and position-controlled inorganic nanomaterials based polymer nanofibers via electrospinning. (2) Investigation of the self-assembled electrospun nanofibers during the process of electrospinning.In the first experimental part, we investigate that how to fabricate metal nanoparticles inside the PVA nanofibers and control the inter-distance between them inside the PVA nanofibers based on the theory of"Macromolecules-Metal Complexes"and"electric-rheology". First of all, we successfully obtain Cu nanoparticles inside PVA nanofibers through in-situ electrospinning. Then, we increase the molar ratio of PVA: Cu (in term of repeating units) to control the sizes of Cu nanoparticles. We find when the molar ratio of PVA: Cu is 40:1; we can obtain Cu/PVA coaxial nanocable. As the molar ratio of PVA: Cu is 42:1, two Cu nanowires can be found inside one PVA nanofiber. Finally, we orderly arrange Cu and Ag nanoparticles inside PVA nanofibers through electric-rheology theory.In the second experimental part, we are engaging in controlling the size and position of metal (semiconductor) nanoparticles based on PAN nanofibers through adjusting the concentration of metal salt and DC voltage. We found that metal (semiconductor) nanoparticles decreased by lowering the concentration of metal salt. At the same time, we found that those metal (semiconductor) nanoparticles were on the outer surfaces of PAN nanofibers for no interactions between their precursors and PAN.In the third experimental part, we successfully obtain Cu2S nanorods and nanoparticles through surface-gas-solid reaction and normal gas-solid reaction. A careful analysis of the resulting structures reveals that a new mechanism called room temperature surface-gas-solid reaction plays an important role in determining the formation of hierarchical nanostructures, which suggests a new means to generate hierarchical nanostructures that may lead to new applications. However, the generality of this mechanism is in research.In the fourth experimental part, we demonstrated that hierarchical macroscopic trees can be obtained with charged polymer nanofibers as building blocks through hydrogen bondings and charge-repulsive forces. These macroscopic trees have successfully broken through the size-limits and spatial-limits of self-assembled structures. The sizes of the macroscopic trees can be controlled by varying the electrospinning time. This is the first time, two different types forces (hydrogen bondings and charge-repulsive forces) have been applied in the hierarchical sel-assembly process. Most importantly, the demonstrated method provide a new route for fabricating the macroscopic hierarchical self-assembly structures, but also an excellent model for future research on macroscopic hierarchically self-assembled structures.In conclusion, we successfully controll the size and position of nanomateraisl based on electrospun nanofibers and obtained their self-assembled aggregation for the first time. We find that (i) the position of nanomaterials based on electrospun nanofibers is mainly depended on the interactions between nanomaterials and polymer, (ii) the hydrogen bondings is important for the self-assembled nanofibers'aggregation. We believe that our work can offer a powerful platform for understanding electrospinning technique.