Jülich Centre for Neutron Science (JCNS) and Institute for Complex Systems (ICS), Forschungszentrum Jülich GmbH, 52428 Jülich, Germany.
Jülich Centre for Neutron Science (JCNS) at Maier Leibnitz-Zentrum, Forschungszentrum Jülich GmbH, 85747 Garching, Germany.
Phys Rev Lett. 2019 Mar 1;122(8):088001. doi: 10.1103/PhysRevLett.122.088001.
A key ingredient within theories focusing on the rheology of entangled polymers is the way how the topological constraints of an entangled chain are lifted by unconstrained segments, i.e., how the constraining tube is dilated. This important question has been addressed by directly measuring the tube diameter d at the scale of the tube by neutron spin echo spectroscopy. The tube diameter d and plateau modulus G_{N}^{0} of highly entangled polyethylene oxide (PEO) chains of volume fraction c that are diluted by low molecular PEO show a concentration dependence d∝c^{a/2} and G_{N}^{0}∝c^{1+a} with an exponent a close to 4/3. This result allows the clear discrimination between different theoretical models that predict 4/3 or other values between 1 and 2 and provides an important ingredient to tube model theories.
在关注缠结聚合物流变性的理论中，一个关键因素是未约束链段解除缠结链拓扑约束的方式，即约束管的扩张方式。这个重要问题已经通过中子自旋回波谱学直接测量了约束管的直径 d 来解决。在体积分数 c 下，由低分子量 PEO 稀释的高度缠结聚乙烯氧化物（PEO）链的管直径 d 和平台模量 G_{N}^{0} 表现出浓度依赖性 d∝c^{a/2} 和 G_{N}^{0}∝c^{1+a}，其中指数 a 接近于 4/3。这一结果可以清楚地区分预测值为 4/3 或 1 到 2 之间其他值的不同理论模型，并为管模型理论提供了一个重要的组成部分。
