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

by Dr Marco Bernabei (Donostia International Physics Center (DIPC), San Sebastian, Spain)

Friday 18 Dec 2009, 11:00 → 13:00 Europe/Rome

Aula Corbino (Dip. di Fisica - Edificio E. Fermi)

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). Criti¬cal nonergodicity parameters, critical temperatures and dynamic exponents are obtained from consistent fits of simulation data to MCT asymptotic laws. The so-obtained MCT λ-exponent increases from standard values for fully-flexible chains to values close to the upper limit for stiffchains. In analogy with systems exhibiting higher-order MCT transitions, we suggest that the observed large λ-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.