Collaborative Research: An Experimental Study of the Dynamics of Heated Contact Lines Using Combined High Resolution Thermography and Interferometry

结合高分辨率热成像和干涉法对受热接触线动力学的实验研究了解蒸发薄膜对于开发用于各种行业的设备是至关重要的，这些行业包括涉及涂层、微电子制造和封装、化学加工和材料开发的设备。虽然理论上对这些薄膜的行为有很好的理解，但由于所涉及的长度尺度非常小，因此从来没有通过直接测量传热和薄膜厚度来验证理论预测。这项研究将首次同时使用两种非常强大和互补的实验技术：1)荧光技术测量接触线附近的温度和热流；2)多波长图像分析干涉/反射测量，使我们能够确定汽液界面的形状，该表面的曲率和曲率梯度，以及接触线前面的吸附膜厚度。这些结果将有助于提高这些过程的效率，最终节省能源、材料和劳动力成本，并将影响许多技术的设计和开发，这些技术通过使用界面能量梯度来控制接触线动力学(例如，热管、未加热和加热表面上的沸腾、扩散和润湿、燃料电池、蒸发诱导自组装、微型化学实验室等)。许多基本问题仍然存在，关于界面区域中能量转移的机制。对于完全润湿的流体，该区域的特点是在接触线前方有一个非常薄的吸附层，在接触线后面有一个气液界面曲率迅速变化的区域，以及一个气液界面曲率相对恒定的主弯月面区域。部分润湿的流体可能有也可能没有被吸附的膜。此外，在加热表面的薄膜中还观察到了接触线的振荡。这项研究将通过利用毛细作用和分离压力引起的界面能量梯度来自然控制简单流体或稀释的理想流体混合物的流动，来解决基本的相变传热和传质问题。关于三相接触线上过程的结构和动力学的理论预测的有效性将被调查。这项工作的目标是：1)用纯流体测量等温弯月面的形状，并将测量得到的分子间力与介质衬底上各种流体的预测值进行比较；2)设计、建立和运行一个实验，测量纯流体加热的半月面内的热流密度分布和曲率，并测试现有的薄膜界面传输理论；3)扩展纯流体的实验，包括稀薄的、理想的混合物，并测试目前关于混合物薄膜中界面传输的理论；4)使用这些技术来表征纯流体和混合物的接触线不稳定性和振荡；以及5)评估分子形状对固液界面滑移的影响程度，从而也影响接触线区域的输运过程。荧光技术将允许直接测量局部热流和温度。干涉/反射测量技术将允许我们记录当能量梯度被扰动时延长的半月面和接触线的形状发生了什么，或者当半月面在表面上移动时，通过表面曲率测量来推断局部热传递。这两种技术必须结合起来，才能获得评估当前界面传输理论所需的数据。

An Experimental Study of the Dynamics of Heated Contact Lines Using Combined High ResolutionThermography and InterferometryUnderstanding of evaporating thin films is essential to the development of devices used in a wide variety of industries including those involved in coating, microelectronics fabrication and packaging, chemical processing, and materials development. Although there is a good theoretical understanding of how these films behave, direct measurements of both the heat transfer and the thin film thickness to verify the theoretical predictions have never been made due to the very small length scales involved. This investigation will simultaneously employ, for the first time, two very powerful and complementary experimental techniques: 1) Fluorescence techniques to measure the temperature and heat flux in the vicinity of the contact line; and 2) Multi-wavelength, image analyzing interferometry/reflectometry that enables us to determine the shape of the vapor-liquid interface, the curvature and curvature gradient of that surface, and the adsorbed film thickness ahead of the contact line. The results will contribute to making these processes more efficient, ultimately saving energy, materials, and labor costs, and will affect the design and development of many technologies that operate by controlling contact line dynamics using interfacial energy gradients (e.g., heat pipes, boiling, spreading and wetting on unheated and heated surfaces, fuel cells, evaporation induced self-assembly, micro-chemical laboratories, etc.).Many fundamental questions remain regarding the mechanisms by which energy is transferred in the interfacial region. With a completely wetting fluid, this region is characterized by a very thin adsorbed layer ahead of the contact line, by a region behind the contact line where the curvature of the vapor-liquid interface rapidly changes, and by a primary meniscus region where the curvature of the vapor-liquid interface is relatively constant. A partially wetting fluid may or may not have the adsorbed film. In addition, oscillations of the contact line have been observed in thin films on heated surfaces. The research will address fundamental phase-change heat and mass transfer questions by using interfacial energy gradients due to capillarity and disjoining pressure to naturally control the flow of simple fluids or dilute, ideal fluid mixtures. The validity of theoretical predictions regarding the structure and dynamics of the processes at the three-phase contact line will be investigated. The objectives of this work are: 1) To measure the shape of isothermal menisci using pure fluids and compare intermolecular forces obtained from those measurements with predicted values for various fluids on dielectric substrates; 2) To design, build, and operate an experiment to measure both the heat flux distribution and curvature as a function of position within the heated meniscus of pure fluids and to test current theories of interfacial transport in thin films; 3) To expand on the experiments with a pure fluid to include dilute, ideal mixtures and to test current theories of interfacial transport in thin films of mixtures; 4) To use these techniques to characterize contact line instability and oscillations for both the pure fluid and mixtures; and 5) To evaluate the degree to which molecular shape affects slip at the solid liquid interface and hence also affects transport processes in the contact line region. The fluorescence technique will allow direct measurement of the local heat flux and temperature. The interferometry/reflectometry technique will allow us to record what happens to the shape of the extended meniscus and the contact line as that energy gradient is perturbed, or to infer the local heat transfer from surface curvature measurements as the meniscus moves over the surface. Both techniques must be combined to obtain the data required to assess the current theories of interfacial transport.