We have developed a computational methodology [P.S. Stephanou, C. Baig, G. Tsolou, V.G. Mavrantzas, and M. Kröger, J. Chem. Phys., 132, 124904 (2010)] which allows one to calculate the most important function in the reptation or tube theory, the segment survival probability function ψ(s,t) (and its average Ψ(t), the overall tube survival probability), by projecting MD data of atomistically detailed samples to the tube model, thus directly probing mechanisms such as contour length fluctuations (CLFs) and constraint release (CR) on chain relaxation. The computed ψ(s,t) functions can be used next to calculate the linear viscoelastic properties of the melt, such as the zero shear rate viscosity and the spectra of storage and loss moduli, in the framework of the reptation theory. We have applied the approach to a number of polymeric systems such as entangled homopolymer melts of linear polyethylene, cis-1,4-polybutadiene and trans-1,4-polybutadiene, and bidipserse melts of cis-1,4- and trans-1,4-polybutadiene. The results are compared against experimentally measured rheological data and the predictions of modern tube models.
asured rheological data and the predictions of modern tube models.
