Looking inside the entanglement “tube” using molecular dynamics simulations

For 30 years, the dynamics of entangled polymers have been explained using the phenomenological “tube” model, where the “tube” represents the confining effects of surrounding chains, but the tube properties, such as its length and diameter, could only be inferred indirectly by fitting the tube model to rheological data. Now, however, molecular simulations are allowing these properties to be directly computed. The computational advances in molecular dynamics and related methods that have made this possible are here reviewed. In addition, it is discussed how new findings, such as an apparent time dependence of the tube diameter and direct observation of “hopping” of branch points along the tube, are helping to refine the tube model.