原位正电子湮没寿命实验观察聚乙烯连续拉伸过程中自由体积孔的微小尺度演化,Macromolecules

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原位正电子湮没寿命实验观察聚乙烯连续拉伸过程中自由体积孔的微小尺度演化
Macromolecules ( IF 5.1 ) Pub Date : 2023-05-25 , DOI: 10.1021/acs.macromol.3c00486
Dongmei Huang ₁ , Yun Dong ₁ , Hang Guo ₂ , Erjie Yang ₂ , Yiwen Chen ₁ , Mi Luo ₁ , Ziwen Pan ₁ , Jiandang Liu ₁ , Liangbin Li ₂ , Hongjun Zhang ₁ , Bangjiao Ye ₁

Affiliation

使用新开发的正电子湮灭寿命光谱 (PALS) 设备，计数率高达 3000 cps，原位首次对聚合物的连续拉伸过程进行PALS实验，定量分析自由体积孔的微小尺度演化。根据四种不同结晶度聚乙烯的应力应变关系和PALS结果，拉伸过程可分为四个不同的阶段：弹性阶段、初始非线性阶段（直到屈服点）、屈服后阶段和应变硬化阶段。前三个阶段中 o-Ps（正正电子素）寿命的增加表明自由体积孔尺寸随着应变的增加而增大。最后阶段 o-Ps 寿命的减少很可能是由于自由体积空穴的各向异性增加所致。相对自由体积分数 FFV _r（源自孔半径R（根据Tao-Eldrup模型计算）和o-Ps强度）通常在前两个阶段增加，但在其他两个阶段几乎保持不变。这项工作展示了未来通过原位PALS 实验揭示材料微观结构微小尺度演化的新可行性。

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Minute-Scale Evolution of Free-Volume Holes in Polyethylenes during the Continuous Stretching Process Observed by In Situ Positron Annihilation Lifetime Experiments

Using the newly developed positron annihilation lifetime spectroscopy (PALS) facility with a high count rate up to 3000 cps, in situ PALS experiments were performed for the first time on the continuous stretching process of polymers to quantitatively analyze the minute-scale evolution of free-volume holes. According to the stress–strain relationship and PALS results of four types of polyethylenes with different crystallinities, the tensile process could be divided into four distinct stages: elastic, initial nonlinear (until yield point), postyield, and strain hardening stages. The increase of o-Ps (orthopositronium) lifetime in the first three stages exhibits an enlargement of free-volume hole size with increasing strain. The decrease of the o-Ps lifetime in the last stage is most probably due to the increasing anisotropy of free-volume holes. The relative fractional free volume FFV_r (derived from hole radius R (calculated from the Tao–Eldrup model) and o-Ps intensity) generally increases in the first two stages but remains nearly unchanged in the other two stages. This work demonstrates a new feasibility to disclose minute-scale evolution of microstructure of materials through in situ PALS experiments in the future.

更新日期：2023-05-25

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