Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
Instituto Pluridisciplinar, Universidad Complutense de Madrid, Paseo de Juan XXIII 1, 28040 Madrid, Spain.
Int J Mol Sci. 2023 Jan 23;24(3):2276. doi: 10.3390/ijms24032276.
The concentration dependence of the surface tension of several binary mixtures of non-electrolytes has been measured at 298.15 K. The mixtures have been chosen since they presented a so-called "W-shape" concentration dependence of the excess constant pressure heat capacity and high values of the concentration-concentration correlation function. This behavior was interpreted in terms of the existence of anomalously high concentration fluctuations that resemble those existing in the proximities of critical points. However, no liquid-liquid phase separation has been found in any of these mixtures over a wide temperature range. In this work, we have extended these studies to the liquid-air interfacial properties. The results show that the concentration dependence of the surface tension shows a plateau and the mixing surface tension presents a "W-shape" behavior. To the best of our knowledge, this is the first time that this behavior is reported. The weak anomalies of the surface tension near a liquid-liquid critical point suggest that the results obtained cannot be considered far-from-critical effects. The usual approach of substituting the activity by the concentration in the Gibbs equation for the relative surface concentration has been found to lead to large errors and the mixtures to have a fuzzy and thick liquid/vapor interface.
在 298.15 K 下测量了几种非电解质二元混合物的表面张力对浓度的依赖关系。之所以选择这些混合物，是因为它们表现出所谓的“W 形”过剩定压热容浓度依赖性和浓度-浓度相关函数的高值。这种行为是根据异常高浓度波动的存在来解释的，这些波动类似于临界点附近存在的波动。然而，在很宽的温度范围内，这些混合物中都没有发现液-液分相。在这项工作中，我们将这些研究扩展到了液-气界面性质。结果表明，表面张力对浓度的依赖关系呈现出一个平台，混合表面张力呈现出“W 形”行为。据我们所知，这是首次报道这种行为。在接近液-液临界点时表面张力的微弱异常表明，所得到的结果不能被认为是远离临界点的影响。通常将活度代替 Gibbs 方程中的浓度用于相对表面浓度的方法会导致较大的误差，并且混合物具有模糊和厚的液/气界面。
