Energy transport at solid-gas,-vapour and-liquid interfaces: the role of adsorption

随着纳米技术的发展，在分子水平上理解界面现象变得越来越重要。先前发现基金的研究结果表明，蒸汽吸附物是由分子簇组成的，而不是通常认为的分子层。后者导致气相压接近饱和蒸汽压的极限达到一个令人尴尬的无穷大。采用分子簇概念推导了Zeta吸附等温线（ZAI）。在最近的CRD拨款的帮助下，ZAI被证明消除了无限性，并导致了实验强烈支持的预测。在本提案中，我们计划将ZAI扩展到一个未开发的领域：从平衡蒸气吸附到冷凝，或者换句话说，从平衡吸附到稳定的非平衡吸附。我们已经迈出了第一步，推导出了当气相相对于固体界面过冷时可以应用的非平衡ZAI的表达式。我们已经进行了一系列的稳态初步实验，以确定我们计划的实验程序的可行性，以检验非平衡ZAI实验。当硅表面相对硅表面过冷时，将光滑的硅表面暴露在庚烷蒸气中。用干涉仪测量吸附膜的厚度；用安装在定位千分尺上的微型热电偶测量蒸汽温度；通过在Si衬底中植入12个热电偶来测定表面温度。这些测量表明，在每次稳定的冷凝实验中，界面温度都是不连续性的。当相变发生在界面上时，界面温度不连续现在是预期的结果，在这种情况下是冷凝。当过冷达到某一特定值时，观察到相变：虽然还不是被吸附的液体，但被吸附的气相变厚了约50倍。在固体表面相对于蒸汽过冷的情况下，我们建议进行三个项目，目的是研究非平衡条件下固体-流体界面的界面能量传递。这三个项目的题目是：1)非平衡吸附和界面相变；2)固气界面能量输运；3)固液界面纳米气泡稳定机理。第三个项目被认为是研究固液界面能量输运之前的必要研究。

As technology has advanced to the nano scale, understanding interfacial phenomena at the molecular level has become more important. Results from a previous Discovery Grant, proposed that vapour adsorbates consist of molecular-clusters, rather than molecular layers, as usually assumed. The latter had led to an embarrassing infinity in the limit of the vapour-phase pressure approaching the saturation-vapour pressure. The molecular-cluster concept was used to derive the Zeta adsorption isotherm (ZAI). With the aid of a recent CRD grant, the ZAI was shown to eliminate the infinity, and to lead to predictions that were strongly supported experimentally. In this proposal, we plan to extend the ZAI to an unexplored area: from equilibrium vapour adsorption to condensation, or in other words, from equilibrium adsorption to steady, non-equilibrium adsorption. We have made a first step by deriving an expression for a non-equilibrium ZAI that can be applied when the vapour phase is supercooled relative to the solid interface. We have conducted a series of steady-state, preliminary experiments to establish the feasibility of our planned experimental procedure for examining the non-equilibrium ZAI experimentally. A smooth silicon surface was exposed to heptane vapour when it was supercooled relative silicon surface. The thickness of the adsorbed film was measured with a interferometer; the vapour temperature was measured with a micro-thermocouple mounted on a positioning micrometer; and the surface temperature was determined using 12 thermocouples implanted in the Si substrate. These measurements indicated an interfacial temperature discontinuity during each steady, condensation experiment. An interfacial temperature discontinuity is now the expected result when a phase change is occurring at an interface, condensation in this case. When the supercooling reached a particular value, a phase transition was observed: the adsorbed vapour phase became ~ 50 times thicker, although not yet an adsorbed liquid. With a solid surface was supercooled relative to a vapour, we propose to conduct to three projects with the objective of investigating interfacial energy transport at solid-fluid interfaces under non-equilibrium conditions. The three projects are entitled:1) Non-equilibrium adsorption and interfacial phase transitions; 2) Interfacial energy transport at solid-vapour interfaces; and 3) Mechanism of nano bubble stability at solid-liquid interfaces. The third project is viewed as a necessary study before examining interfacial energy transport at solid-liquid interfaces.