電紡織高分子纖維受退火作用後之形態轉變

Abstract

電紡織是一種簡單且方便製作高分子纖維的技術，可利用不同電紡織參數製造不同尺寸纖維。目前不同電紡織纖維已被用在各種應用上，但是高分子纖維加熱退火效應較少被學者們研究。退火效應可控制高分子纖維性質及表面形態。我們選用poly(methyl methacrylate) (PMMA)以及polystyrene (PS)作為電紡織高分子纖維材料，探討退火效應對其形態從纖維轉變成微米球體的影響。首先藉由參數控制，製得不同形態之電紡織纖維，之後再進行兩個不同實驗主題的研究探討。

實驗主題一主要探討電紡織纖維在無基板環境中加熱退火，使用乙二醇溶劑作為均勻加熱介質，可避免基板的作用，並探討雷利不穩定效應對形態轉變之影響。在此我們使用不同加熱退火時間以及各種加熱退火溫度作控制，使高分子纖維發生形態轉換最終轉變至圓球狀，並符合雷利不穩定理論計算結果。亦使用不同分子量高分子纖維，探討加熱退火時間對於分子量高低之影響。實驗主題二則是探討電紡織纖維於基板上進行加熱退火，研究電紡織纖維於不同基板表面的介面能差異，使其加熱退火後發生雷利不穩定效應以及各介面能之差異，最終形成微米等級微粒，其直徑大小亦符合理論推算結果。並利用選擇性溶劑移除基板，觀察微粒真實面貌，並判定其發生機制。

Electrospinning is a simple and convenient technique to prepare polymer fibers, and various electrospun polymer fibers have been generated for different applications. But the annealing effect of the polymer fibers, which is critical for controlling the properties and morphologies of the polymer fibers, has been rarely studied. Here we study the annealing effect of electrospun poly(methyl methacrylate) (PMMA) and polystyrene (PS) fibers and their transformation into microspheres or microparticles under thermal annealing. The polymer fibers are first prepared by electrospinning and the diameters of the electrospun fibers are controlled by the electrospinning condition.

In part 1, polymer fibers are annealed in ethylene glycol. The fibers undulate and transform into microspheres, driven by Rayleigh instability. The morphology can be controlled by using different annealing times and annealing temperatures. The sizes of the microspheres are found to be fitted well with the theoretical calculations. Polymers with different molecular weights are also used to investigate the effect of molecular weights.

In part 2, we study the annealing effect of the electrospun fibers on different substrates. Various morphology transformations are obtained by annealing the fibers on different substrates, and the relationship between the polymer interfacial energy and the Rayleigh instability is studied. The polymer fibers transform into microparticles caused by the reduction of the interface energy, and the sizes of particles also fit well with the theoretical values. The shapes of the polymer particles are confirmed by removing the polymer film using selective solvent. Both AFM and SEM show that hemispherical polymer particles can be formed by annealing PS fibers on PMMA film coated substrates.