The characterization of fluid phase transitions in nanoscale pores remains a challenging problem that can significantly affect various applications, such as drug delivery, carbon dioxide storage, and enhanced oil recovery. Previous theoretical and experimental studies have shown that the fluid phase transition changes drastically when the fluid is confined within nanocapillaries with dimensions of <10 nm, potentially due to the dominance of fluid–surface interactions compared to bulk effects. However, due to challenges in performing experiments at the nanoscale, there have been limited experimental observations of the phase transition at this scale. Recent advances in lab-on-a-chip (LOC) technology have enabled the observation of many nanoscale phenomena. In this study, for the first time, we present the direct observation and visualization of n-butane vapor–liquid phase transitions in a 2 nm slit pore using LOC technology. Our experiments, for the first time, measured and directly visualized the deviation of the vapor–liquid phase transition pressure in a 2 nm slit pore compared to the associated unconfined or bulk value. We also measured the liquid–vapor phase transition pressure and observed a significant difference from the vapor–liquid phase transition pressure. We complemented our experimental observations with grand canonical ensemble Monte Carlo molecular simulations to understand the underlying molecular-level mechanisms.

中文翻译：

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直接观察 2 nm 纳米通道中的汽液相变和滞后现象

纳米级孔隙中流体相变的表征仍然是一个具有挑战性的问题，它可以显着影响各种应用，例如药物输送、二氧化碳储存和提高石油采收率。先前的理论和实验研究表明，当流体被限制在尺寸小于 10 nm 的纳米毛细管内时，流体相变会发生巨大变化，这可能是由于流体 - 表面相互作用与体积效应相比占主导地位。然而，由于在纳米尺度上进行实验的挑战，在这个尺度上对相变的实验观察有限。片上实验室 (LOC) 技术的最新进展使人们能够观察到许多纳米级现象。在这项研究中，我们首次展示了直接观察和可视化使用 LOC 技术在 2 nm 狭缝孔中的正丁烷汽液相变。我们的实验首次测量并直接可视化了 2 nm 狭缝孔中的汽液相变压力与相关的无侧限或体积值相比的偏差。我们还测量了液相 - 气相相变压力，并观察到与气相 - 液相转变压力的显着差异。我们用大规范集合蒙特卡罗分子模拟补充了我们的实验观察，以了解潜在的分子水平机制。