Research Initiation Awards: Study of Thermal Phenomena at Interfaces

对薄膜和已加工金属等固体表面在微米和纳米尺度上的粗糙度测量表明，这些表面在几十年的长度尺度上是粗糙和无序的。在湍流界面上也观察到了类似的特征。这种无序结构强烈地影响着界面上的热现象。以往对这类界面热现象的研究，通常要么过于简单化地将界面的光滑性理想化，要么求助于经验和半经验的分析方法。这种对这些现象缺乏物理理解的主要原因是无法量化这些结构中的无序。这项研究建议使用新的概念的分形几何来理解和表征无序表面的基本性质。这种表征在一定范围内量化了每个长度尺度上的表面结构。这在提供有关长度尺度上的热现象与界面相互作用的关键洞察方面尤其重要。将分形学应用于接触电导的初步研究已经解释了以前的几个实验结果。基于这些令人鼓舞的前景，这项研究建议使用分形学来研究具有科学和工程意义的界面热现象，如接触电导、摩擦加热和辐射与表面的相互作用。

Roughness measurements of solid surfaces, such as thin films and machined metals, at microscales and nanoscales show that the surfaces are rough and disordered over several decades of length scales. Similar features have been observed in turbulent fluid interfaces. Such disordered structures strongly influence thermal phenomena at interfaces. Previous studies on thermal phenomena at such interfaces have conventionally made either oversimplifying idealizations of smoothness of an interface or resorted to empirical and semi- empirical methods of analysis. This lack of physical understanding of the phenomena was mainly due to an inability to quantify the disorder in these structures. This study proposes to use the novel concepts of fractal geometry to understand and characterize the fundamental nature of disordered surfaces. Such a characterization quantifies the structure of surfaces at every length scale within certain limits. This is particularly important in providing key insight into the interactions of thermal phenomena with interfaces at relevant length scales. Preliminary studies on applying fractals in contact conductance have explained several previous experimental results. Based on these encouraging prospects, this study proposes to use fractals to study interfacial thermal phenomena of scientific and engineering importance such as contact conductance, frictional heating, and interactions of radiation with surfaces.