Chain Dynamics of Bidisperse Polyethylene Melts:  A Monte Carlo Study on a High-Coordination Lattice

• Published in: Macromolecules 2007-02, Vol.40 (4), p.959-966
• Main Authors: Lin, Heng, Mattice, Wayne L, von Meerwall, Ernst D
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Rheology and viscoelasticity
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma062088s

The dynamics of bidisperse (1K/4.5K) polyethylene (PE) melts in the Rouse-reptation transitional region is studied using a newly designed dynamic Monte Carlo algorithm on a high-coordination (2nnd) lattice. The internal relaxation modes fit the KWW relationship very well. The distinctive dynamic transitions have been identified on the basis of mode analysis. The observed anomalous power law dependence of higher modes agrees very well with other earlier molecular dynamics simulations using united atom models. For the long-chain component in the mixture, the tube dilation concept has been visualized through the short-time diffusion of monomers at different concentration, although the established tube dilation theory seems to be not applicable to this transitional region. The diffusion coefficients have been calculated in real time units over the full concentration range for this mixture of PE. Converting Monte Carlo steps into real time units was based on a previously determined coefficient at the simulation temperature. The results are tested against both the Hess theory generalized by Rathgeber et al. and the von Meerwall/Pearson model. Both models fit our data reasonably well. The two-step relaxation of internal modes predicted by the Hess theory can be vaguely identified in the simulation but cannot be faithfully designated due to the data fluctuation near the zero of the relevant autocorrelation function.