| The development of modern science and technology leads to the fast development of nano technology. In recent decades, the fabrication, characterization and application of nanomaterials have achieved great progress. For now, nanomaterials have already been widely used in regenerative medicine, biology, clinical field and biochemical analysis, efficient energy field and aerospace. Nanofibers were one of the most important branches of nano technology science. Due to the good mechanical properties, high specific surface area, high porosity and good conductivity of properties, they have attracted more and more attentions. The properties of fibres were dependant on the structure of the fibres. To get better properties of the fibers, researchers have devoted much of their careers to studying the structures of the fibers.This thesis focused on fabricating micro-/nanofibers possessing multilevel structures based on the combination of traditional electrospinning technology and the microfluidic system, and before experiments, the finite element method were used to analyze and evaluate the motion of the fluid in the microfluidic, offering a theoretical guidance to the following experiments. Polyvinyl alcohol (PVA), polylactic acid (PLA) and polyethylene glycol (PEG) have been used in meterial preparation for their better biocompatibility and biodegradability. Fibers with controllable hydrophobic/hydrophilic cooperative Janus branched polymer fiber structures or inner multilevel structures were finally fabricated based on this microfluidic-electrospinning technique.In Chapter two, the basic theory of finite element analysis (FEA) in the motion of fluid is introduced. According to the following experimental mcirofludic devices, FEA were employed to simulate the flow field in the micrfludic devices during the fabrication of micro-droplets in two different ways:capillary of microfluidic and T-shaped structure of microfluidic. Based on the T microfluidic model, the variation of the flow field were analysized more deeply under different boundary conditions, the continuous phase with different concentration and the discontinuous phase with different speed, on ANSYS software. The results of this simulation offered a theoretical guide to the following experiment.In Chapter three, the PVA aqueous solution (as dispersing phase) and PLA solution (PLA in organic solvent dimethyl carbonate (DMC), as continuous phase) were injected into microfluidic chip, after the PVA droplets were generated, PLA solution containing PVA droplets will be delivered to the stainless needle applied with a electrostatic voltage. Then the electrospun hydrophobic/hydrophilic cooperative Janus branched polymer fibers are obtained. We investigated the fiber structures with light microscopes, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). In order to further investigate the formation mechanism of multilevel structured fibers and to build a model of Janus branched polymer fibers, it is necessary to understand the distribution of electric field. Based on the principle of the finite element,2D electric field analysis are analyzed to validate the branched polymer fibers generated by the finite element ANSYS software. Based on the above works, different density and length of branches can be obtained by changing the parameters in process. As a result, the controllable preparation of Janus branched polymer fibers can be achieved.In Chapter four, PEG aqueous solution (as dispersing phase) and PLA solution (PLA in organic solvent dimethyl carbonate (DMC), as continuous phase) were injected into Microfluidic chip. By modulating parameters in experiments, a novel structured model, inner multilevel structur is obtained. |
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