科研之友
微信
新浪微博
Facebook
分享链接
摘要
The 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 PIBmain-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 alpha-relaxation regime has delivered the dynamic exponents of the theory-in particular, the exponent parameter lambda-the critical non-ergodicity parameters, and the critical temperature T-c. The obtained values of lambda and T-c agree, within the uncertainties involved in both studies, with those deduced from depolarized light scattering experiments [A. Kisliuk et al., J. Polym. Sci. Part B: Polym. Phys. 38, 2785 (2000)]. Both,. and T-c/T-g values found for PIB are unusually large with respect to those commonly obtained in low molecular weight systems. Moreover, the high T-c/T-g value is compatible with a certain correlation of this parameter with the fragility in Angell%26apos;s classification. Conversely, the value of. is close to that reported for real polymers, simulated %26quot;realistic%26quot; 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.
- 出版日期2013-10-4
