Surface tensions at elevated pressure depend strongly on bulk phase saturation
Surface tensions at elevated pressure depend strongly on bulk phase saturation
复制标题
高压下的表面张力很大程度上取决于体相饱和度
DOI：
10.1016/j.jcis.2021.02.114
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发表时间：
2021
影响因子：
9.9
通讯作者：
Alvarez, Nicolas J.
中科院分区：
文献类型：
--
作者：
Hinton, Zachary R.;Alvarez, Nicolas J.
理解高压下的界面现象对于各种过程的设计、重要系统的建模和界面热力学的解释是至关重要的。虽然许多先前的研究提供了对这些领域的见解，但目前的技术存在固有的缺陷，限制了平衡测量。在这项工作中，我们将Alvarez和同事的环境微张力计改造成高压微张力计（HPMT），能够在高压下实验量化各种界面现象。特别是，HPMT使用一个微型球形界面固定在毛细管的尖端，通过拉普拉斯方程直接测量表面张力。用于对系统加压的微尺度气泡流确保在进行测量之前快速饱和体相。通过测量空气-水的表面张力作为压力的函数，验证了HPMT。然后，我们测量了二氧化碳蒸汽和水的表面张力作为压力的函数，发现平衡表面张力值比文献中最初报道的要低。这项工作不仅进一步发展了一种有用的实验技术，用于探测高压下的界面现象，而且证明了建立体积平衡来测量表面张力的重要性。二氧化碳-水表面的真实平衡状态比以前报道的张力要低。我们假设这种差异可能是由于使用传统的张力测量法确保散装流体饱和所需的长扩散时间尺度。因此，我们认为以前报道的高压测量是在非平衡条件下进行的，从而消除了文献中长期存在的差异。我们的测量为纯二氧化碳-水表面建立了平衡压力等温线，这对于分析表面活性剂在高压下的输送至关重要。
HypothesisUnderstanding interfacial phenomena at elevated pressure is crucial to the design of a variety of processes, modeling important systems, and interpreting interfacial thermodynamics. While many previous studies have offered insight into these areas, current techniques have inherent drawbacks that limit equilibrium measurements.ExperimentsIn this work, we adapt the ambient microtensiometer of Alvarez and co-workers into a high pressure microtensiometer (HPMT) capable of experimentally quantifying a wide range of interfacial phenomena at elevated pressures. Particularly, the HPMT uses a microscale spherical interface pinned to the tip of a capillary to directly measure surface tension via the Laplace equation. The stream of microscale bubbles used to pressurize the system ensures quick saturation of the bulk phases prior to conducting measurements. The HPMT is validated by measuring the surface tension of air–water as a function of pressure. We then measure the surface tension of CO2vapor and water as a function of pressure, finding lower equilibrium surface tension values than originally reported in the literature.FindingsThis work both introduces further development of a useful experimental technique for probing interfacial phenomena at elevated pressures and demonstrates the importance of establishing bulk equilibrium to measure surface tension. The true equilibrium state of the CO2-water surface has a lower tension than previously reported. We hypothesize that this discrepancy is likely due to the long diffusion timescales required to ensure saturation of the bulk fluids using traditional tensiometry. Thus we argue that previously reported elevated pressure measurements were performed at non-equilibrium conditions, putting to rest a long standing discrepancy in the literature. Our measurements establish an equilibrium pressure isotherm for the pure CO2-water surface that will be essential in analyzing surfactant transport at elevated pressures.