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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Molecular Dynamics of Benzene in Neat Liquid and a Solution Containing Polystyrene. ~(13)C Nuclear Magnetic Relaxation and Molecular Dynamics Simulation Results
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Molecular Dynamics of Benzene in Neat Liquid and a Solution Containing Polystyrene. ~(13)C Nuclear Magnetic Relaxation and Molecular Dynamics Simulation Results

机译：苯在纯净液体和含聚苯乙烯溶液中的分子动力学。 〜（13）C核磁弛豫和分子动力学模拟结果

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摘要

The reorientational motion of benzene in the neat liquid and in a polystyrene/benzene solution was investigated by NMR relaxation as well as MD simulation methods. The temperature-dependent ~(13)C dipolar spin-lattice relaxation rates and cross correlation rates between the dipolar relaxation mechanism and the relaxation by chemical-shift anisotropy were measured. From the NMR measurements and MD simulation results, the rotational diffusion constants for rotations about the C_6 axis and perpendicular to it were evaluated, and it was found that the values of the former were larger than those of the latter. The rotational anisotropy, which is the ratio of these values, decreases for the NMR data from 2.3 to 1.2 when increasing the temperature from 280 to 323 K. The activation energy for reorientation about the main symmetry axis was 3.4 kJ mol~(-1) and about axes perpendicular to that 13.3 kJ mol~(-1). The temperature effect was less pronounced for the MD results; the anisotropy changed from 1.9 to 1.3 between 280 and 360 K. The reorientational correlation functions showed a significant non-Debye behavior and were fitted with a Kohlrausch-Williams-Watts function. Furthermore, from the MD simulations the temperature dependence of the density and the translational diffusion coefficient were also determined. The NMR data for benzene rotational motions in a polystyrene matrix could not be explained by a simple rotational diffusion model. From the data, it was concluded that the rotations about the C_6 axis were much faster than about axes perpendicular to the C_6 axis. This finding is in accordance to a previous MD study by Muller-Plathe.
机译：通过NMR弛豫和MD模拟方法研究了纯净液体和聚苯乙烯/苯溶液中苯的方向性运动。测量了温度相关的〜（13）C偶极自旋晶格弛豫速率以及偶极弛豫机理与化学位移各向异性弛豫之间的互相关率。从NMR测量和MD模拟结果，评估绕C_6轴并垂直于C_6轴的旋转的旋转扩散常数，发现前者的值大于后者。当温度从280 K升高到323 K时，NMR数据的旋转各向异性（即这些值的比率）从2.3降低到1.2。围绕主对称轴重新取向的活化能为3.4 kJ mol〜（-1）并围绕垂直于该轴13.3 kJ mol〜（-1）的轴。 MD结果对温度的影响不太明显。各向异性在280和360 K之间从1.9更改为1.3。方向相关函数显示出显着的非德拜行为，并配备了Kohlrausch-Williams-Watts函数。此外，从MD模拟中，还确定了密度的温度依赖性和平移扩散系数。聚苯乙烯基体中苯旋转运动的NMR数据无法通过简单的旋转扩散模型来解释。从数据得出的结论是，绕C_6轴的旋转比绕垂直于C_6轴的旋转快得多。这一发现与Muller-Plathe先前的MD研究一致。

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