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Applicability of mode-coupling theory to polyisobutylene: A molecular dynamics simulation study

AuthorsKhairy, Yasmin; Álvarez González, Fernando ; Arbe, Arantxa ; Colmenero de León, Juan
Issue Date2013
PublisherAmerican Physical Society
CitationPhysical Review E 88: 042302 (2013)
AbstractThe applicability of Mode Coupling Theory (MCT) to the glass-forming polymer polyisobutylene (PIB) has been explored by using fully atomistic molecular dynamics simulations. MCT predictions for the so-called asymptotic regime have been successfully tested on the dynamic structure factor and the self-correlation function of PIB main-chain carbons calculated from the simulated cell. The factorization theorem and the time-temperature superposition principle are satisfied. A consistent fitting procedure of the simulation data to the MCT asymptotic power-laws predicted for the α-relaxation regime has delivered the dynamic exponents of the theory - in particular, the exponent parameter λ - the critical non-ergodicity parameters, and the critical temperature Tc. The obtained values of λ and Tc agree, within the uncertainties involved in both studies, with those deduced from depolarized light scattering experiments. Both, λ and T c/Tg values found for PIB are unusually large with respect to those commonly obtained in low molecular weight systems. Moreover, the high Tc/Tg value is compatible with a certain correlation of this parameter with the fragility in Angell's classification. Conversely, the value of λ is close to that reported for real polymers, simulated >realistic> polymers and simple polymer models with intramolecular barriers. In the framework of the MCT, such finding should be the signature of two different mechanisms for the glass-transition in real polymers: intermolecular packing and intramolecular barriers combined with chain connectivity. © 2013 American Physical Society.
Publisher version (URL)http://dx.doi.org/10.1103/PhysRevE.88.042302
Identifiersdoi: 10.1103/PhysRevE.88.042302
issn: 1539-3755
e-issn: 1550-2376
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