| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 101 === Electrospinning technique is a convenient, simple, and fast method to fabricate polymer nanofibers or microfibers. The sizes and morphologies of electrospun fibers can be controlled by adjusting the experimental parameters in the electrospinning process. Currently, various electrospun polymer fibers have been generated and are widely used for different applications. But the annealing effect of electrospun polymer fibers has been little studied. Here we choose polystyrene (PS) and poly(methyl methacrylate) (PMMA) as materials for electrospinning, and we study the substrate effect on the morphology transformation of the electrospun polymer fibers under thermal and solvent annealing.
In this thesis, we first investigate the morphology transformation of electrospun PS fibers on glass and PMMA-coated glass substrates by thermal annealing. The final morphologies are induced by the Rayleigh instability and are affected by the interfacial energies between different substrates. When electrospun PS fibers are annealed on glass substrates, wetting occurs. When the electrospun PS fibers are annealed on PMMA-coated glass substrates, the PS fibers transform into hemispheres embedded in the PMMA film, driven by the Rayleigh instability. The morphology transformation can also be observed by selectively removing PS or PMMA. In addition, Stimulated Raman Scattering (SRS) is applied to further confirm the mechanism of the morphology transformation.
In addition, we study the morphology transformation of electrospun PS fibers by thermal annealing and solvent annealing on bare and treated silicon wafers. In the experiments of thermal annealing, PS fibers are found to wet on three different silicon wafers. In the experiments of solvent annealing, however, the morphology transformation is dependent on the types of the annealing solvents and the underlying substrates. For example, PS fibers are converted to beads-on-string PS structures by annealing the PS fibers on ODTS-treated silicon wafers under toluene annealing.
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