The Role of Intramolecular Barriers on the Glass Transition of Polymers: Computer Simulations vs. Mode Coupling Theory

Abstract

We present computer simulations of a simple bead-spring model for polymer melts with intramolecular barriers. By systematically tuning the strength of the barriers, we investigate their role on the glass transition. Dynamic observables are analyzed within the framework of the Mode Coupling Theory (MCT). Critical nonergodicity parameters, critical temperatures and dynamic exponents are obtained from consistent fits of simulation data to MCT asymptotic laws. The so-obtained MCT $\lambda$-exponent increases from standard values for fully-flexible chains to values close to the upper limit for stiff chains. In analogy with systems exhibiting higher-order MCT transitions, we suggest that the observed large $\lambda$-values arise form the interplay between two distinct mechanisms for dynamic arrest: general packing effects and polymer-specific intramolecular barriers. We compare simulation results with numerical solutions of the MCT equations for polymer systems, within the polymer reference interaction site model (PRISM) for static correlations. We verify that the approximations introduced by the PRISM are fulfilled by simulations, with the same quality for all the range of investigated barrier strength. The numerical solutions reproduce the qualitative trends of simulations for the dependence of the nonergodicity parameters and critical temperatures on the barrier strength. In particular, the increase of the barrier strength at fixed density increases the localization length and the critical temperature. However the qualitative agreement between theory and simulation breaks in the limit of stiff chains. We discuss the possible origin of this feature.

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Cited by in corpus (6)

• Molecular dynamics simulations of glassy polymers
• A First Principle Approach to Rescale the Dynamics of Simulated Coarse-Grained Macromolecular Liquids
• From caging to Rouse dynamics in polymer melts with intramolecular barriers: a critical test of the Mode Coupling Theory
• Glassy dynamics of a binary Voronoi fluid: A mode-coupling analysis
• Glass formation in mechanically interlocked ring polymers: the role of induced chain stiffness
• Static and dynamic contributions to anomalous chain dynamics in polymer blends