Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain.
J Chem Phys. 2009 Nov 28;131(20):204502. doi: 10.1063/1.3266852.
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 in 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.
我们呈现了一种简单的珠-簧模型的计算机模拟，用于研究具有分子内障碍的聚合物熔体。通过系统地调整障碍的强度，我们研究了它们对玻璃化转变的作用。在模式耦合理论（MCT）的框架内分析了动态观测值。通过将模拟数据与 MCT 渐近定律的一致拟合，得到了临界非遍历参数、临界温度和动态指数。由此获得的 MCT lambda 指数从完全柔性链的标准值增加到接近刚性链上限的值。与表现出高阶 MCT 转变的系统类似，我们认为观察到的大 lambda 值源自两种不同的动态俘获机制之间的相互作用：一般的堆积效应和聚合物特定的分子内障碍。我们将模拟结果与聚合物参考相互作用位点模型（PRISM）中用于静态相关的 MCT 方程的数值解进行了比较。我们验证了模拟满足 PRISM 引入的近似，对于所有研究的障碍强度范围，其质量相同。数值解再现了模拟中非遍历参数和临界温度对障碍强度依赖性的定性趋势。特别是，在固定密度下增加障碍强度会增加局域化长度和临界温度。然而，理论和模拟之间的定性一致性在刚性链的极限处破裂。我们讨论了这种特征的可能起源。
