基板效應對高分子電紡織纖維形態轉變之影響

Abstract

電紡織技術是一種方便、簡單、又可快速製備高分子奈米或微米纖維的方法，可以利用調整參數來控制纖維的尺寸及形貌。目前電紡織纖維已經被廣泛地應用在許多不同的領域上，但是很少有學者探討高分子電紡織纖維在不同退火環境下其形態的影響，因此這裡我們探討當高分子纖維在不同的基板上進行退火處理時其形態的變化。在此我們選用polystyrene (PS)以及poly(methyl methacrylate) (PMMA)作為電紡織高分子纖維材料，並利用熱退火(thermal annealing)和溶劑退火(solvent annealing)來探討基板效應對於高分子電紡織纖維形態轉變的影響。 本論文主要是探討PS電紡織纖維在不同基板上進行熱退火與溶劑退火後的形態變化，基板的選用首先為玻璃以及不同厚度的PMMA高分子膜，以探討利用不同基板的介面能以及雷利不穩定效應對纖維最終形態的影響。當PS電紡織纖維在玻璃上加熱時，產生潤濕現象(wetting)。當PS電紡織纖維在PMMA膜上加熱時，纖維因雷利不穩定現象轉變為陷入PMMA膜中的PS半球。形態的轉變也可以利用選擇性移除其中一個高分子來觀察，此外我們也利用受激式拉曼散射(SRS, Stimulated Raman Scattering)來幫助了解高分子的形態轉變，並判定其發生機制。 此外我們也探討PS電紡織纖維在矽基板與處理過之矽基板上受到熱退火與溶劑退火的形態變化。在熱退火實驗中發現，PS纖維在三種不同矽基板上皆發生潤濕現象。當使用溶劑退火時，根據使用的溶劑或基板的不同，PS纖維會有不同的形態轉變。舉例來說，當使用甲苯當溶劑及ODTS改質過的矽基板，PS纖維會形成串珠結構(beads-on-string)。

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.