Determine tube diameter by measuring entropy tensile force

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.