The effect of traces of ethanol in supercritical carbon dioxide on the mixture's thermodynamic properties is studied by molecular simulations and Taylor dispersion measurements. This mixture is investigated along the isobar p = 10 MPa in the temperature range between T = 304 and 343 K. Along this path, the mixture undergoes two transitions: First, the Widom line is crossed, marking the transition from liquid-like to gas-like conditions. A second transition occurs from the supercritical gas-like domain to a subcritical gas. The Widom line crossover entails inflection points for most of the studied properties, i.e. density, enthalpy, shear viscosity, Maxwell–Stefan and intradiffusion coefficients. On the other hand, the transition between the super- and subcritical regions is found to be generally smooth, an observation that is qualitatively confirmed by experimental Taylor dispersion measurements. Dedicated atomistic simulations show the presence of microheterogeneities due to ethanol self-association along the investigated path, which lead to the mixture's anomalous behavior in its extended critical region.

中文翻译：

---

二氧化碳-乙醇混合物在扩展的临界区域中的扩散

通过分子模拟和泰勒分散测量研究了超临界二氧化碳中痕量乙醇对混合物热力学性质的影响。在T = 304和343 K之间的温度范围内，沿着等压线p = 10 MPa研究了该混合物。沿着该路径，混合物经历了两个过渡：首先，穿过Widom线，标志着从液态到气态的过渡。类似的条件。从超临界气体样域到亚临界气体发生第二次转变。Widom线的交叉需要大多数研究特性的拐点，即密度，焓，剪切粘度，麦克斯韦-斯特凡和内部扩散系数。另一方面，发现超临界区和亚临界区之间的过渡通常是平滑的，这一观察结果通过实验泰勒色散测量得到了定性的确认。专用的原子模拟表明，由于乙醇沿研究路径的自缔合，存在微观异质性，从而导致混合物在其扩展的临界区域内出现异常行为。