One Dimensional Nanounites Assembled By Electrospinning Technique And The Assemblies’ Properties

Electrospinning technique can facilely fabricate one-dimensional (1D) nanomaterials on a large scale and the morphology can be controlled, especially a variety of composite nanofibers can be synthesized by directly adding functional components into the electrospinning solution, which overcomes the disadvantage of the conventional synthesis methods for1D nanomaterials. On the other hand, several reports found that anisotropic nanostructures, such as carbon nanotubes, were aligned along the axis of the electrospun fibers, thus it is possible to use electrospinning technique as a kind of assemble method. So far, although the nanomaterials have superior properties to those of their bulk counterparts, it still remains a challenge that assembling of these individual nanocomponents into macroscopic materials in a large scale and keeps the stability of the assemblies.This dissertation will focused on combining and assembling1D functional nanounites effectively with electrospun fibers by electrospinning technique, and the properties of the1D composite nanofibers were investigated. By electrospinning several kind of ID nanounites, composite nanofibers were successfully fabricated, which confirms the electrospinning technique could assemble1D nanounites in large scale and has the advantage of broad applicability, efficiency and stability. The main results can be summarized as follows:1. A novel assemble route was developed for aligning gold nanorods (AuNRs) within polyvinyl alcohol (PVA) fibers by electrospinning technique. After electrospinning, AuNRs were confined within the PVA fibers and aligned along the axial of the electrospun fibers, which confirms AuNRs can be effectively assembled by elelctrospinning technique. Compared with some traditional assemble methods, electrospinning technique has shown obvious advantages in simple operation and can assemble on a large scale. By varying the AuNRs concentration in the electrospun solution, the space among the AuNRs confined within the polymer fibers could be adjusted and therefore the optical properties of the AuNR/PVA electrospun mats could be controlled. Compared with the AuNRs solution and corresponding casting films, both the transverse Plasmon band (TPB) and the longitudinal Plasmon band (LPB) of the electrospun mat red shifted; when increasing the AuNRs concentrations, the LPB of the electrospun mats blue shifted and broadened, while there is no significant change on TPB, which confirms the effect of assemble on their optical properties. In addition, the electrospun mat could be used as surface enhanced Raman scattering (SERS) substrate. The resulting electrospun mat makes a significant SERS enhancement to3,3’-diethylthiatricarbocyanine iodide (DTTCI) molecules with large-area uniformity and good reproducibility. Lastly, PVA electrospun fibers were crosslinked, and the composite films have remarkable photothermal effect. Under808nm irradiation, the composite film with dimension of10×5mm2could heat1mL water from23℃to50℃in60s, and most of the cancer cells could be injured in30s, which confirms the Au/PVA composite films have the advantage of high efficiency and can be used facilely.2. Composite nanounites were electrospun and assemble within the polymer fibers. Firstly, we fabricated the nanocomposites composed of the same dimensional but different components, such as AuNR-AgNW assemblies, in which the AuNRs were arranged along the axis of the AgNWs with a preferential string-like alignment. The assembled AuNR-AgNW nanocomposites are then further embedded within PVA nanofibers by electrospinning, by which both AuNRs and AgNWs can be stabilized and arranged along the axis of polymer nanofibers. The influences of the AuNR-AgNW assemblies with different AuNRs concentrations on the optical properties and SERS enhancement have been investigated. Compared with the normal casting films composed of randomly dispersed AuNRs and AgNWs, or electrospun mats with monometallic components, the resulting AuNR-AgNW/PVA electrospun mats show red-shifted and broader absorption bands, also higher SERS performances, due to the order alignment of AuNR-AgNW nanocomposites on a large scale. Secondly, electrospinning was used to assemble the nanocomposites composed of the same components, such as Au/SiO2/Au nanoparticles. The nanocomposites were also aligned within the electrospun fibers, and the performance of the composite mats could be varied by etching the SiO2layer.3. Ultralong NWs were further macroscopic-scale aligned by using the magnetic-field-assisted electrospinning technique. With this method, ultrolong AgNWs can be assembled within the PVP electrospun fibers and arranged in parallel; The number of AgNWs confined within the PVP fibers can be controlled by changing the concentration of NWs within the electrospun solution; While the polymer nanofibers can also be arranged by the magnetic-assisted-field electrospinning technique, the AgNWs were manipulated to align parallel to each other throughout the entire film. The AgNWs can be further aligned as a result of the flexibility of the polymer fibers, and mats with tunable cross angle and the fiber assemblies with hierarchical structures can be prepared. Due to the high EM field existing in adjacent AgNWs, the polarization angle of the incident light strongly influences the UV-vis transmission spectra for the mats, which further confirms the effectively assemble of NWs by electrospinning technique. In addition, ultrathin TeNWs were electrospun to confirm that the electrospinning technique could not only assemble rigid NWs, but also the flexible ones.When chosing the non-benign solvent of TeNWs to solve the polymer and electrospinning, the TeNWs could be assembled like a bundle within the electrospun fibers. The obtained composite fibers could be used as microreactor, as TeNWs have high reactivity.