Electrospun polymer core–shell fibers have gained much attention because of their promising applications in areas such as electronic devices, drug delivery, and tissue engineering. The morphology transformation of polymer core–shell fibers, however, has been rarely investigated. Here, we study the effect of thermal annealing on the morphology transformation of electrospun polystyrene (PS)/poly(methyl methacrylate) (PMMA) core–shell fibers on PMMA films. Two types of transformation processes are discovered. In the first type of the transformation process (type I), the PS cores transform to hemispherical particles after the annealing process; in the second type of the transformation process (type II), the PS cores transform to spherical particles after the annealing process. The measured sizes of the hemispherical and spherical PS domains fall into two classified regions, as predicted for the two different types of transformation processes. It is also observed that the growth rates of the undulated amplitude are similar for the two different types of transformation processes, but the type I fibers start to undulate at later annealing times than the type II fibers do. When the PS particles are selectively removed, the PMMA films with linearly arranged cavities are used for the tearing experiments, demonstrating a proof of concept on the potentials in studying the mechanical properties of cavity-containing films.

中文翻译：

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从电纺聚合物核-壳纤维到聚合物半球形和球形：两种转变过程和具有线性排列腔的撕裂薄膜

电纺聚合物核-壳纤维由于在电子设备，药物输送和组织工程等领域的应用前景广阔而备受关注。然而，很少研究聚合物核-壳纤维的形态转变。在这里，我们研究了热退火对PMMA薄膜上的电纺聚苯乙烯（PS）/聚甲基丙烯酸甲酯（PMMA）核-壳纤维形态转变的影响。发现了两种类型的转换过程。在第一种类型的转变过程（类型I）中，PS核在退火过程之后转变为半球形粒子；在第二种类型的转变过程（II型）中，PS核在退火过程之后转变为球形颗粒。如针对两种不同类型的转换过程所预测的那样，所测量的半球形和球形PS域的大小分为两个分类区域。还观察到，对于两种不同类型的转变过程，起伏幅度的增长率是相似的，但是I型纤维在比II型纤维更晚的退火时间开始起伏。当PS颗粒被选择性地去除，该PMMA膜与直线排列的腔被用于撕裂实验，证明在研究含有空腔的膜的机械特性的概念上的电位证明。还观察到，对于两种不同类型的转变过程，起伏幅度的增长率是相似的，但是I型纤维在比II型纤维更晚的退火时间开始起伏。当PS颗粒被选择性地去除，该PMMA膜与直线排列的腔被用于撕裂实验，证明在研究含有空腔的膜的机械特性的概念上的电位证明。还观察到，对于两种不同类型的转变过程，起伏幅度的增长率是相似的，但是I型纤维在比II型纤维更晚的退火时间开始起伏。当PS颗粒被选择性地去除，该PMMA膜与直线排列的腔被用于撕裂实验，证明在研究含有空腔的膜的机械特性的概念上的电位证明。