Graduate School of Engineering, Nagoya University, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan.
NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Chem Phys. 2017 Jun 28;146(24):244506. doi: 10.1063/1.4990408.
The role of the prepeak structure of liquid methanol in determining its shear viscosity was studied by means of molecular dynamics (MD) simulation and mode-coupling theory (MCT). The autocorrelation function of the shear stress and the intermediate scattering functions at both the prepeak and the main peak were calculated from the MD trajectories. Their comparison based on MCT suggests that the viscoelastic relaxation in the ps regime is affected by the slow structural dynamics at the prepeak. On the other hand, the MCT for molecular liquids based on the interaction-site model (site-site MCT) fails to describe the coupling between the prepeak dynamics and shear stress. The direct evaluation of the coupling between the two-body density and the shear stress reveals that the viscoelastic relaxation is actually affected by the prepeak dynamics, although the coupling is not captured by the site-site MCT. The site-site MCT works well for a model methanol without partial charges, suggesting that the failure of the site-site MCT originates from the existence of a hydrogen-bonding network structure.
采用分子动力学（MD）模拟和模式耦合理论（MCT）研究了液体甲醇的预峰结构在确定其剪切粘度中的作用。从 MD 轨迹中计算了剪切应力的自相关函数和预峰和主峰处的中间散射函数。基于 MCT 的比较表明，ps 区间的粘弹性弛豫受到预峰处缓慢结构动力学的影响。另一方面，基于相互作用位点模型（位点位 MCT）的分子液体 MCT 无法描述预峰动力学和剪切应力之间的耦合。对两体密度和剪切应力之间耦合的直接评估表明，尽管位点位 MCT 没有捕捉到这种耦合，但粘弹性弛豫实际上受到预峰动力学的影响。对于没有部分电荷的模型甲醇，位点位 MCT 效果很好，这表明位点位 MCT 的失败源于氢键网络结构的存在。
