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

随着技术向纳米尺度发展，在分子水平上理解界面现象变得更加重要。之前的一次发现授予的结果提出，蒸气吸附物质由分子簇组成，而不是通常假设的分子层。后者导致了令人尴尬的是，气相压力的极限接近饱和蒸气压力。利用分子簇概念推导了Zeta吸附等温线(ZAI)。在最近CRD拨款的帮助下，ZAI被证明消除了无穷大，并导致了实验上强有力的支持的预测。在这个提议中，我们计划将ZAI扩展到一个未知的领域：从平衡蒸汽吸附到冷凝，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，推导出了当汽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稳态的初步实验，以确定我们计划的实验程序的可行性，以实验地检验非平衡ZAI。当相对硅表面过冷时，光滑的硅表面暴露在庚烷蒸汽中。用干涉仪测量吸附膜的厚度；用安装在定位测微仪上的微型热电偶测量蒸汽温度；用植入硅衬底的12个热电偶测量表面温度。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的。现在，当界面发生相变时，界面温度不连续是预期的结果，在这种情况下是冷凝。当过冷度达到某一特定值时，观察到一个相变：被吸附的汽相变厚约50倍，尽管还不是被吸附的液体。由于固体表面相对于蒸气是过冷的，我们建议进行三个项目，目的是研究非平衡条件下固-液界面上的界面能量传输。这三个项目分别是：1)非平衡吸附和界面相变；2)固-汽界面上的界面能量传输；3)固-液界面上纳米气泡的稳定性机理。第三个项目被认为是在考察固-液界面上的界面能量传输之前的必要研究。在我们研究的每一年中，我们计划让2名研究生和1名本科生分别完成这三个项目。如果我们的研究成功的话。我们预计，在工业过程中使用冷凝对加拿大工业具有根本性的重要性。

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. During each year of our study, we plan for 2 graduate students and 1 undergraduate student to work on each of the three project. If our study is successful. we expect it to be of fundamental importance to Canadian industry using condensation in their industrial processes.