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

结合高分辨率热成像和干涉测量技术对加热接触线动态特性的实验研究了解蒸发薄膜对于开发各种工业中使用的设备是必不可少的，这些工业包括涂层、微电子制造和包装、化学加工和材料开发。虽然有一个很好的理论理解，这些薄膜的行为，直接测量的传热和薄膜厚度，以验证理论预测从来没有作出由于涉及的非常小的长度尺度。这项研究将首次同时采用两种非常强大和互补的实验技术：1）荧光技术来测量接触线附近的温度和热流;以及2）多波长、图像分析干涉测量/反射测量，其使我们能够确定汽-液界面的形状、该表面的曲率和曲率梯度，以及接触线前方的吸附膜厚度。结果将有助于使这些过程更有效，最终节省能源、材料和劳动力成本，并且将影响通过使用界面能量梯度控制接触线动态来操作的许多技术的设计和开发（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、蒸发诱导的自组装、微化学实验室等）。关于能量在界面区域中传递的机制，仍然存在许多基本问题。对于完全润湿的流体，该区域的特征在于接触线前方的非常薄的吸附层、接触线后方的汽-液界面曲率迅速变化的区域以及汽-液界面曲率相对恒定的主弯月面区域。部分润湿的流体可以具有或可以不具有吸附的膜。此外，在加热表面上的薄膜中观察到接触线的振荡。该研究将解决基本的相变传热和传质问题，通过使用由于毛细作用和分离压力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。理论预测的结构和动力学的过程中，在三相接触线的有效性将进行调查。本工作的目的是：1）用纯流体测量等温线的形状，并将测量所得的分子间力与各种流体在介质基片上的预测值进行比较; 2）设计，建造，并进行实验以测量作为纯流体的加热弯月面内的位置的函数的热通量分布和曲率，并测试3）将纯流体的实验扩展到包括稀释的理想混合物，并检验混合物薄膜中界面输运的现有理论; 4）利用这些技术表征纯流体和混合物的接触线不稳定性和振荡;以及5）评估分子形状影响固液界面处的滑移并因此也影响接触线区域中的输运过程的程度。荧光技术将允许直接测量局部热通量和温度。干涉测量/反射测量技术将允许我们记录当能量梯度被扰动时扩展的弯月面和接触线的形状发生了什么，或者当弯月面在表面上移动时从表面曲率测量推断局部热传递。这两种技术必须结合起来，以获得所需的数据，以评估目前的理论界面传输。

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.