Kapnistos M, Lang M, Vlassopoulos D, Pyckhout-Hintzen W, Richter D, Cho D, Chang T, Rubinstein M
FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 71110, Greece.
Nat Mater. 2008 Dec;7(12):997-1002. doi: 10.1038/nmat2292. Epub 2008 Oct 26.
After many years of intense research, most aspects of the motion of entangled polymers have been understood. Long linear and branched polymers have a characteristic entanglement plateau and their stress relaxes by chain reptation or branch retraction, respectively. In both mechanisms, the presence of chain ends is essential. But how do entangled polymers without ends relax their stress? Using properly purified high-molar-mass ring polymers, we demonstrate that these materials exhibit self-similar dynamics, yielding a power-law stress relaxation. However, trace amounts of linear chains at a concentration almost two decades below their overlap cause an enhanced mechanical response. An entanglement plateau is recovered at higher concentrations of linear chains. These results constitute an important step towards solving an outstanding problem of polymer science and are useful for manipulating properties of materials ranging from DNA to polycarbonate. They also provide possible directions for tuning the rheology of entangled polymers.
经过多年的深入研究，纠缠聚合物运动的大多数方面已被理解。长线性和支化聚合物具有特征性的缠结平台，它们的应力分别通过链的蠕动或支链回缩而松弛。在这两种机制中，链端的存在至关重要。但是没有链端的纠缠聚合物如何松弛其应力呢？通过使用适当纯化的高摩尔质量环状聚合物，我们证明这些材料表现出自相似动力学，产生幂律应力松弛。然而，浓度几乎比其重叠浓度低二十倍的痕量线性链会导致增强的机械响应。在较高浓度的线性链下会恢复缠结平台。这些结果是解决聚合物科学一个突出问题的重要一步，并且对于操纵从DNA到聚碳酸酯等材料的性能很有用。它们还为调节纠缠聚合物的流变学提供了可能的方向。
