State Key Lab of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Renmin St 5625, Changchun 130022, Jilin, China.
ACS Macro Lett. 2022 Apr 19;11(4):484-490. doi: 10.1021/acsmacrolett.2c00072. Epub 2022 Mar 22.
Molecular theories for dynamics of entangled polymers are based on both the number of Kuhn segments per entanglement and the number of entanglements per chain /. Extensive studies have shown that, for polymer chains in the solutions or melts, linear viscoelasticity can be properly normalized, whereas the nonlinear extensional rheological properties cannot be normalized when / is kept the same. The failure of the latter normalization has been attributed to a difference in . Nevertheless, nonlinear rheological studies are lacking for a suitable model system with fixed and /. In this study, we identify poly(-alkyl methacrylate)s with the number of carbons per alkyl group below seven as a model system. We find that the degree of the transient strain hardening during extensional flow strengthens with increasing the size of the alkyl group even when and / are kept the same, which is attributable to the weaker friction reduction when the main backbones are more separated.
分子理论对于缠结聚合物的动力学的研究基于每缠结的 Kuhn 段数和每链的缠结数。广泛的研究表明，对于溶液或熔体中的聚合物链，线性粘弹性可以得到适当的归一化，而当保持不变时，非线性拉伸流变性能不能归一化。这种归一化的失败归因于的差异。然而，对于具有固定和的合适模型体系，非线性流变学研究仍然缺乏。在本研究中，我们将烷基甲基丙烯酸酯的数量确定为每个烷基基团的碳原子数低于七作为模型体系。我们发现，在拉伸流动过程中，瞬态应变硬化的程度随着烷基基团尺寸的增大而增强，即使保持和不变，这归因于当主链更加分离时，摩擦减少得更弱。
