Nanosized crystals induced by secondary crystallization are common occurrences in semicrystalline polymers. However, their significance is often overlooked due to their small proportion and the difficulty in distinguishing them from primary crystals (PCs). This study selected poly(vinylidene fluoride) (PVDF) as a model system. We distinguished the thickness of the SCs from that of the PCs based on small-angle X-ray scattering data and further built the relationship between the melt memory of α-PVDF materials and the crystallinity of nanosized α-phase SCs by adjusting the end crystallization temperature. Notably, these nano α-SCs exhibit a remarkable role in transitioning from TGTG′ to T₃GT₃G′ conformation during their partial melting and subsequent cooling process. The conformational transition stemming from the partial melting of the SCs effectively promotes the transition from the nonpolar α-phase to the polar γ-phase. The observed phase transition can be attributed to the matching between the melting thermal dynamics of α-SCs and the thermal dynamics of the conformational transition within amorphous chains. Our findings underscore the significant effect of moderate nanosized SCs on the phase transformation and introduce a practical and effective methodology for producing polar-phase PVDF materials.

中文翻译：

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特异性纳米次生晶体对熔融记忆诱导的聚偏二氟乙烯相变的决定性作用


由二次结晶诱导的纳米级晶体在半结晶聚合物中很常见。然而，由于它们的比例小并且难以与初级晶体 （PC） 区分开来，它们的重要性经常被忽视。本研究选择聚偏二氟乙烯 （PVDF） 作为模型系统。我们基于小角 X 射线散射数据区分了 SCs 和 PC 的厚度，并通过调整末端结晶温度进一步构建了 α-PVDF 材料的熔融记忆与纳米级 α 相 SCs 结晶度之间的关系。值得注意的是，这些纳米 α-SCs 在其部分熔化和随后的冷却过程中，在从 TGTG' 过渡到 T₃GT₃G′ 构象中表现出显着的作用。由 SCs 部分熔化引起的构象转变有效地促进了从非极性 α 相到极性 γ 相的转变。观察到的相变可归因于 α-SCs 的熔融热动力学与非晶链内构象转变的热动力学之间的匹配。我们的研究结果强调了中等纳米 SCs 对相变的显着影响，并介绍了一种生产极性相 PVDF 材料的实用有效的方法。