Thickness-Dependent Mechanical Failure in Thin Films of Glassy Polymer Bidisperse Blends
Thickness-Dependent Mechanical Failure in Thin Films of Glassy Polymer Bidisperse Blends
复制标题
玻璃态聚合物双分散共混物薄膜中与厚度相关的机械故障
DOI：
10.1021/acs.macromol.1c01630
复制
发表时间：
2022
期刊：
影响因子：
5.5
通讯作者：
Riggleman, Robert A.
中科院分区：
文献类型：
--
作者：
Zhang, Tianren;Riggleman, Robert A.
虽然许多研究已经分析了玻璃态聚合物薄膜的各种性质，但其失效模式和非线性力学响应直到最近才受到关注。由于缠结密度的降低和自由表面附近流动性的增加之间的竞争效应，人们不清楚是否应该预期脆化或改善延展性。在这项研究中，我们构建了一个双分散的分子量分布的聚合物薄膜，通过将短链作为稀释剂高度缠结的聚合物系统在不同的组合物和膜厚度。由于自由表面附近的高流动性区域的主导地位，约10个单体直径厚的膜比由双分散共混物或均聚物组成的较厚的膜的延展性小，尽管具有类似的缠结密度。当薄膜大于20σ时，薄膜的力学性能对厚度的依赖性很弱，特别是对于高纠缠系统。随着稀释剂聚合物的添加，膜变得不那么延展性，并且聚合物薄膜的机械性能在添加的稀释剂是未缠结的聚合物时受到最大影响，如所预期的。此外，我们观察到的自由表面和纠缠网络之间的竞争效应，其中自由表面的相互作用占主导地位的最薄的薄膜测试的机械行为，而纠缠网络在较厚的薄膜中起着主导作用。
Although many studies have analyzed the various properties of glassy polymer thin films, the failure mode and nonlinear mechanical response have only recently received attention. Due to competing effects between reductions in the entanglement density and increased mobility near the free surfaces, it is not clear whether one should anticipate embrittlement or improved ductility. In this study, we constructed polymer thin films with a bidisperse molecular weight distribution by incorporating short chains as diluents into highly entangled polymer systems at different compositions and film thicknesses. Due to the dominance of the high-mobility region near the free surfaces, films approximately 10 monomer diameters thick are less ductile than thicker films composed of either a bidisperse blend or a homopolymer, despite having a similar entanglement density. The dependence of mechanical properties on the thickness is weak when the film is larger than 20σ, especially for highly entangled systems. With diluent polymers added, the films become less ductile, and the mechanical properties of the polymer thin films are affected most when the added diluents are unentangled polymers, as expected. Further, we observe a competing effect between the free surface and entanglement network, where the free surface interaction dominates the mechanical behavior for the thinnest films tested while the entanglement network plays a dominant role in thicker films.
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