Nasrabad Afshin Eskandari, Laghaei Rozita, Eu Byung Chan
Department of Chemistry and RQMP, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada.
J Phys Chem B. 2005 Apr 28;109(16):8171-9. doi: 10.1021/jp044393q.
In previous work on the density fluctuation theory of transport coefficients of liquids, it was necessary to use empirical self-diffusion coefficients to calculate the transport coefficients (e.g., shear viscosity of carbon dioxide). In this work, the necessity of empirical input of the self-diffusion coefficients in the calculation of shear viscosity is removed, and the theory is thus made a self-contained molecular theory of transport coefficients of liquids, albeit it contains an empirical parameter in the subcritical regime. The required self-diffusion coefficients of liquid carbon dioxide are calculated by using the modified free volume theory for which the generic van der Waals equation of state and Monte Carlo simulations are combined to accurately compute the mean free volume by means of statistical mechanics. They have been computed as a function of density along four different isotherms and isobars. A Lennard-Jones site-site interaction potential was used to model the molecular carbon dioxide interaction. The density and temperature dependence of the theoretical self-diffusion coefficients are shown to be in excellent agreement with experimental data when the minimum critical free volume is identified with the molecular volume. The self-diffusion coefficients thus computed are then used to compute the density and temperature dependence of the shear viscosity of liquid carbon dioxide by employing the density fluctuation theory formula for shear viscosity as reported in an earlier paper (J. Chem. Phys. 2000, 112, 7118). The theoretical shear viscosity is shown to be robust and yields excellent density and temperature dependence for carbon dioxide. The pair correlation function appearing in the theory has been computed by Monte Carlo simulations.
在先前关于液体输运系数的密度涨落理论的工作中，有必要使用经验自扩散系数来计算输运系数（例如二氧化碳的剪切粘度）。在这项工作中，消除了在计算剪切粘度时对自扩散系数进行经验输入的必要性，从而使该理论成为一个自成体系的液体输运系数分子理论，尽管它在亚临界区域包含一个经验参数。液态二氧化碳所需的自扩散系数是通过使用修正的自由体积理论来计算的，该理论将通用的范德华状态方程和蒙特卡罗模拟相结合，借助统计力学精确计算平均自由体积。它们已作为密度的函数沿着四条不同的等温线和等压线进行了计算。使用了Lennard-Jones位点-位点相互作用势来模拟分子二氧化碳的相互作用。当将最小临界自由体积与分子体积确定为相同时，理论自扩散系数的密度和温度依赖性与实验数据显示出极好的一致性。然后，通过采用早期论文（《化学物理杂志》2000年，112卷，7118页）中报道的剪切粘度的密度涨落理论公式，将如此计算得到的自扩散系数用于计算液态二氧化碳剪切粘度的密度和温度依赖性。理论剪切粘度显示出很强的适用性，并且对二氧化碳产生了极好的密度和温度依赖性。该理论中出现的对关联函数已通过蒙特卡罗模拟进行了计算。
