Schappert Klaus, Pelster Rolf
FR Physik, Universität des Saarlandes, Campus E2.6, 66123 Saarbrücken, Germany.
ACS Omega. 2020 Apr 21;5(17):9649-9657. doi: 10.1021/acsomega.9b03565. eCollection 2020 May 5.
For sorption studies, the saturation vapor pressure above an adsorbate is of great significance. For example, it is needed for the determination of the pore size distribution, the Laplace pressure, and the chemical potential. Above the bulk triple point, , this pressure is identical with the saturation vapor pressure above the bulk liquid. However, below , the correct value of () is controversial. Nanoconfined fluids exhibit a shift of the freezing and melting temperatures in comparison to the bulk state. Thus, the adsorbed fluid is supercooled in a certain temperature range below . Here, we show that it is possible to determine the appropriate saturation vapor pressure above the nanoconfined supercooled liquid experimentally. For this purpose, we have performed sorption measurements with liquid argon in nanoporous Vycor glass in the temperature range of the supercooled liquid and at temperatures above the bulk triple point. In order to determine the unknown and temperature-dependent saturation vapor pressure of the supercooled confined adsorbate, (), we use the Kelvin equation relating this quantity to the pore radius, ( ), that is independent of temperature. The knowledge of the absolute values for the liquid-vapor surface tension of the supercooled adsorbate, γ(), is not required. However, we presuppose that its dependence on the unknown vapor pressure, γ( ), is bulk-like. Our results indicate that the saturation vapor pressure above the supercooled nanoconfined liquid corresponds to that above supercooled bulk argon (i.e., to the pressure obtained by an extension of the usual vaporization curve to < ). We expect that this method can be used for the determination of above other supercooled adsorbates.
对于吸附研究而言，吸附质上方的饱和蒸气压具有重要意义。例如，测定孔径分布、拉普拉斯压力和化学势时都需要用到它。在体相三相点以上，此压力与体相液体上方的饱和蒸气压相同。然而，在体相三相点以下，其正确值存在争议。与体相状态相比，纳米限域流体的凝固和熔化温度会发生偏移。因此，被吸附流体在低于体相三相点的一定温度范围内会过冷。在此，我们表明通过实验确定纳米限域过冷液体上方的合适饱和蒸气压是可行的。为此，我们在过冷液体温度范围以及高于体相三相点的温度下，对纳米多孔Vycor玻璃中的液态氩进行了吸附测量。为了确定过冷受限吸附质未知的且与温度相关的饱和蒸气压 ，我们使用开尔文方程，该方程将此量与与温度无关的孔径 相关联。不需要知道过冷吸附质的液 - 气表面张力的绝对值γ( )。然而，我们假定其对未知蒸气压的依赖关系γ( )类似于体相情况。我们的结果表明，过冷纳米限域液体上方的饱和蒸气压与过冷体相氩上方的饱和蒸气压相对应（即与通过将通常的汽化曲线延伸至 < 所得到的压力相对应）。我们预计该方法可用于确定其他过冷吸附质上方的 。
