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

随着技术发展到纳米尺度，在分子水平上理解界面现象变得更加重要。来自先前发现资助的结果提出，蒸气吸附物由分子簇组成，而不是通常假设的分子层。后者导致蒸汽相压力接近饱和蒸汽压的极限为令人尴尬的无穷大。使用分子簇概念推导出Zeta吸附等温线（ZAI）。在最近的CRD资助的帮助下，ZAI被证明可以消除无穷大，并导致实验强烈支持的预测。在本提案中，我们计划将ZAI扩展到未开发的领域：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。我们已经取得了第一步，推导出一个表达式的非平衡ZAI，可以应用时，汽相相对于固体界面过冷。我们已经进行了一系列的稳态，初步的实验，以建立我们计划的实验程序的可行性，实验研究非平衡ZAI。光滑的硅表面在相对于硅表面过冷时暴露于庚烷蒸气中。吸附膜的厚度用干涉仪测量;蒸汽温度用安装在定位测微计上的微型热电偶测量;并且表面温度用植入Si衬底中的12个热电偶确定。这些测量结果表明，在每个稳定的界面温度不连续，冷凝实验。界面温度不连续性现在是当在界面处发生相变时的预期结果，在这种情况下是冷凝。当过冷度达到特定值时，观察到相变：吸附的气相变得厚约50倍，尽管还不是吸附的液体。由于固体表面相对于蒸气是过冷的，我们提出了三个项目，目的是研究非平衡条件下固-流界面处的界面能输运。这三个项目的标题是：1）非平衡吸附和界面相变; 2）在固-汽界面的界面能量传输;和3）在固-液界面的纳米气泡稳定性机制。第三个项目被认为是一个必要的研究之前，检查在固-液界面的界面能量传输。在我们的研究中，我们每年计划2名研究生和1名本科生从事这三个项目。如果我们的研究成功。我们希望它对加拿大工业在其工业过程中使用冷凝具有根本的重要性。 **

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. **