Lamellar splaying is an important non-crystallographic branching phenomenon in polymer spherulite growth. The origin of lamellar splaying is commonly attributed to the repulsive action caused by cilia, but recent studies using solid nuclear magnetic resonance indicate that there are no cilia in the amorphous phase between adjacent lamellae. In order to further understand the origin of lamellar splaying, we reported a method to prepare poly(L-lactic acid) (PLLA) multilayer lamellae by film isothermal crystallization from the melt state in supercritical CO₂. We obtained screw terrace crystals with three different surface amorphous conformations assembled from three PLLA samples with different molecular weights. According to the characterization results of atomic force microscopy, transmission electron microscopy, nuclear magnetic resonance and X-ray diffraction, three kinds of intercrystalline phases were determined as no fold, tight fold, and loose fold. It was further found that the no fold and tight fold rarely contribute to lamellar splaying of PLLA, but the loose fold on the lamellar surface obviously contributes to lamellar splaying of PLLA. Furthermore, the molecular weight dependence and film thickness dependence of the PLLA crystal form indicated that the loose fold may be caused by the limit of in-plane entanglements in the lamellar thickening growth.

中文翻译：

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折叠构象对超临界CO2中膜结晶的PLLA层状张开的影响

层状张开是聚合物球晶生长中的重要非晶体分支现象。层状张开的起源通常归因于纤毛引起的排斥作用，但是最近使用固体核磁共振的研究表明，相邻薄片之间的非晶相中没有纤毛。为了进一步了解层状张开的起源，我们报道了一种通过在超临界CO _2中从熔融态进行膜等温结晶来制备聚（L-乳酸）（PLLA）多层片的方法。。我们从三个具有不同分子量的PLLA样品中获得了具有三个不同表面非晶构象的梯形梯状晶体。根据原子力显微镜，透射电子显微镜，核磁共振和X射线衍射的表征结果，确定三种晶间相为无褶皱，紧密褶皱和疏松褶皱。进一步发现，无褶皱和紧密褶皱很少有助于PLLA的层状张开，但是层状表面上的松散褶皱显然有助于PLLA的层状张开。此外，PLLA晶体形式的分子量依赖性和膜厚度依赖性表明，松弛折叠可能是由于层状增厚生长中的平面内缠结的限制引起的。