Confined Segmental Diffusion in Nanophase Separated Janus Polynorbornenes as Investigated by Quasielastic Neutron Scattering,Macromolecules

当前位置： X-MOL 学术 › Macromolecules › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

Confined Segmental Diffusion in Nanophase Separated Janus Polynorbornenes as Investigated by Quasielastic Neutron Scattering
Macromolecules ( IF 5.1 ) Pub Date : 2024-08-22 , DOI: 10.1021/acs.macromol.4c01045
Paulina Szymoniak ₁ , Mohamed A. Kolmangadi ₁ , Martin Böhning ₁ , Bernhard Frick ₂ , Markus Appel ₂ , Richard A. Mole ₃ , Nicolas R. De Souza ₃ , Reiner Zorn ₄ , Andreas Schönhals _{1,

5}

Affiliation

A combination of neutron time-of-flight and neutron backscattering spectroscopy was used to investigate the molecular dynamics of Janus polynorbornenes (Janus poly(tricyclononenes)) on a microscopic level. These Janus polynorbornenes, denoted as PTCNSiOR, have a semirigid backbone with −Si(OR)₃ side groups attached to it. R represents the length of the alkyl side chain. Here side chain lengths of R = 3 (propyl) and R = 8 (octyl) were considered. It is worth mentioning that these polymers have some potential as active layers in gas separation membranes, especially for the separation of higher hydrocarbons. The combination of time-of-flight and backscattering will ensure a reasonably broad time window for analysis where the incoherent intermediate scattering function S_Inc(q,t) is considered. Previously, it was shown by X-ray investigations that the system undergoes a nanophase separation into alkyl side chain-rich domains surrounded by a backbone-rich matrix. For PTCNSiOPr (R = 3), the alkyl side-chain-rich domains are truly isolated in the backbone-rich matrix, whereas for PTCNSiOOc (R = 8) these domains percolate through the matrix. Further, it was also previously shown that the alkyl side-chain-rich domains undergo a glass transition. The advantage of neutron scattering experiments discussed here is that besides temporal also spatial information is obtained which will allow conclusions to be drawn about the type of molecular fluctuations. At the lowest measured temperature, the decay in S_inc(q,t) is due to the methyl group rotation. The methyl group dynamics is analyzed in terms of a modified jump-diffusion in a 3-fold potential and yields to a reasonable fraction of hydrogens which contribute to the methyl group rotation. At higher temperatures, the decay in S_Inc(q,t) is due to both the methyl group rotation and the segmental dynamics in the alkyl side-chain-rich domains. The segmental diffusion is modeled by a sublinear diffusion. For the analysis of the scattering function S_Inc(q,t) of PTCNSiOPr an elastic scattering due to the immobilized backbone-rich matrix must be taken into account. The analysis reveals that the segmental dynamics is confined by the finite size of alkyl chain-rich domains and that it is intrinsically heterogeneous in nature. Both effects are more pronounced for PTCNSiOPr in comparison to those of PTCNSiOOc.

中文翻译：

准弹性中子散射研究纳米相分离的 Janus 聚降冰片烯中的受限分段扩散

中子飞行时间和中子背散射光谱相结合，用于在微观水平上研究 Janus 聚降冰片烯（Janus 聚三环壬烯）的分子动力学。这些Janus聚降冰片烯，表示为PTCNSiOR，具有半刚性主链，其上连接有-Si(OR) ₃侧基。 R代表烷基侧链的长度。这里考虑R = 3（丙基）和R = 8（辛基）的侧链长度。值得一提的是，这些聚合物具有作为气体分离膜活性层的潜力，特别是对于高级烃的分离。飞行时间和后向散射的结合将确保在考虑非相干中间散射函数S _Inc ( q , t ) 的情况下进行分析时有一个相当宽的时间窗口。此前，X射线研究表明，该系统经历了纳米相分离，形成富含烷基侧链的区域，周围环绕着富含主链的基质。对于 PTCNSiOPr ( R = 3)，富含烷基侧链的结构域真正隔离在富含主链的基质中，而对于 PTCNSiOOc ( R = 8)，这些结构域渗透到基质中。此外，先前还表明富含烷基侧链的区域经历玻璃化转变。这里讨论的中子散射实验的优点是，除了时间信息之外，还可以获得空间信息，这将允许得出关于分子波动类型的结论。在最低测量温度下， S _inc ( q , t ) 的衰减是由于甲基旋转所致。根据 3 倍电势的改进跳跃扩散来分析甲基动力学，并产生有助于甲基旋转的合理分数的氢。在较高温度下， S _Inc ( q , t ) 的衰减是由于甲基旋转和富含烷基侧链的区域中的链段动力学造成的。分段扩散通过次线性扩散进行建模。为了分析 PTCNSiOPr 的散射函数S _Inc ( q , t )，必须考虑由于固定的富含主链的基质而产生的弹性散射。分析表明，链段动力学受到富含烷基链的区域的有限尺寸的限制，并且本质上是异质的。与 PTCNSiOOc 相比，PTCNSiOPr 的这两种效应更为明显。

更新日期：2024-08-22

点击分享查看原文

点击收藏

公开下载

阅读更多本刊新发论文本刊介绍/投稿指南