The macroscopic viscoelastic properties of entangled polymer liquids can be described by the tube theory, and tube diameter is one of the most important quantities in the tube theory. Based on the tube theory, any linear polymer chain immersed in an entangled polymeric liquid is stretched by an entropic force applied on its both chain ends so that the tube surrounding the chain is kept a certain length, and the magnitude of the entropic force is inversely proportional to the tube diameter. We propose a new method to determine tube diameter by measuring the entropic force. This new method shows better accuracy for the grid model compared with other methods. Moreover, this method can be not only used in computer simulations but also achieved in experiments.

缠结的聚合物液体的宏观粘弹性可以通过管理论来描述，管直径是管理论中最重要的量之一。根据管理论，浸在纠缠的聚合物液体中的任何线性聚合物链均会受到施加在链两端的熵力的拉伸，从而使围绕链的管保持一定长度，而熵力的大小则相反与管径成正比。我们提出了一种通过测量熵力来确定管径的新方法。与其他方法相比，此新方法对网格模型显示出更好的准确性。而且，该方法不仅可以用于计算机仿真，而且可以在实验中实现。